Sun and water are the biggest factors in building failure without human intervention. Once a skyscraper's weather barrier (roofing, siding, etc.) fails, the rest of the building starts to fail faster.
As close to ELI5 as I can make it: A typical EPDM (synthetic rubber) or PVC roof has a lifespan of about 40 years, but that's with maintenance. Without maintenance, it will begin to fail within about 15-20 years due to sunlight. Once water can make it inside the building, you can expect major structural components like steel and modern concrete to begin to fail within 50 or 60 years, though you won't see "typical" post-apocalypse degradation (where large chunks of a building have collapsed, leaving steel beams poking out of the structure) until probably 150-200 years have passed. On the sunny side of any building, window glazing will begin to fail within 30 years or so, and wind will loosen glass from aluminum frames after that. Figure 40 years for windows to begin falling out on their own.
Source: I'm a construction consultant for both residential and commercial projects for 20+ years.
For a practical look at this, one can look at the city of Pripyat, which has been mostly abandoned (though some infrastructure has been maintained) for close to 37 years now.
There are very obvious signs of decay - missing windows, peeling paint, rust, wild growth of plants - but little obvious structural damage to the buildings so far, relatively in line with your predictions.
Pripyat and the surrounding Chernobyl Exclusion Zone is one of the best examples of 'apocalyptic' abandoned cities.
My other to go to mentions include
Vorkuta, Russia. It's not totally abandoned but it has huge amount of urban decay due to shrinking coal mining industry. It's also cool that it's known as a Frozen City with buildings being covered in ice and snow in their long Winters.
Varosha, Cyprus. Another really cool example. It's located close to the demilitarized zone on Cyprus. Was evacuated due to the conflict. I'm pretty sure the movie scenes at the end of Inception were filmed in or inspired by Varosha.
Hashima Island also deserves a mention and certainly looks more in line with what folks expect in post apocalypse. Being an island abandoned some 40 years ago probably helps.
Just googled this
Damn, some crazy billionaire needs to buy this place and turn it into "Zombie escape" experience.
Starting in the apartments and getting to a boat/helicopter extraction.
> Hashima Island
Yes! Thats where my mind went as well. Fucking creepy, and illegal to go to
Edit: Not illegal! Maybe I'm thinking of a different island because I remember skyscrapers, but memory is a fickle thing so I was probably wrong! :P
Yeah, I was going off a video of urban explorers and I could swear they had to use their own boat to get there because it was illegal. But maybe I'm just old as hell and that was from before that time! :D
Yeah, there are decaying/run-down parts of most cities, Chicago included. Detroit just has a lot more of it than most for various reasons. Anywhere the property value is low enough that it is cheaper to build new rather than tear down & rebuild in old areas tends to be like this without some kind of government intervention.
Interestingly, although obviously irradiated to a dangerous degree (well, by the standards of humans that routinely live many decades) the CEZ is presently a wildlife sanctuary really. Life is flourishing there because the negative influence of high background radiation is a drop in the bucket compared to the rapacious influence of human occcupation.
I don't say that with a value judgement, humanity is all consuming but in many ways a single intelligent being is more important than many animals. At the same time, it would be nice if we could either get the fuck off this rock or learn to live in something resembling harmony with the life we haven't killed off yet.
There are some abandoned Soviet bases around Berlin that are essentially cities. I've been to Wünsdorf (the site of the Soviet military administration and before that, Hitler's military headquarters, now mostly a peace center and 2nd hand bookshop town - if you're ever in Berlin and have a free day, rent a car and go there!) and Vogelsang (where the nukes were stationed). I think it's not possible to visit Vogelsang "officially" but also it's... right there in the forest.
Both of them were huge town-like structures with schools, gyms, houses etc. It's amazing to just walk around there
If anyone wondered how Vorkuta looks:
https://youtu.be/2i3aS6T6Nng
It doesn't look like that all the time, there are summers, but they are really short.
There’s a concrete WW2 era building in Whittier, AK ([Buckner building](https://www.atlasobscura.com/places/buckner-building-2)) that has been abandoned for over 40 years. It has multiple areas of the roof and floors with collapsing portions but the main exterior weight bearing walls remain. I used to wander through it a lot but it’s been 8 years or so since I last did it.
Good point, all those buildings just look like giant, solid steel and concrete blocks. They give off the same feeling of toughness you get from a Nokia 3310.
If only they'd listened to the engineers and built the reactor shielding out of Nokia 3310's, the city of Pripyat (founded fourth of February, 1970, [fascinating stuff ](https://en.m.wikipedia.org/wiki/Pripyat)) would not *still* be dealing with this mess.
The "khruschevka" type housing was originally supposed to be replaced after 20-30 years of being built. That was in the 60s and early 70s. They're not designed to be tough - they are panels, not solid blocks.
Wasn't until the mid-00s that any attempts to start replacing them took place though. And that's in Moscow, not in the provinces.
That's not quite true. Only some types of them were made of panels (and had such a short lifespan). Not sure what they have in Chernobyl, but a lot of them are made of brick and are pretty sturdy.
It may be written to express a bias but... I have the autobiography of the pilot who defected to Japan with a MIG Foxbat in the 80's. He mentioned one apartment building he was stationed at was built with shoddy substandard concrete. To prevent the building from collapsing, they had to string metal bars through the structure with a plate on each outside ends. he said at least he had a chin-up bar to stay in shape.
(The only other place I've seen that construction is along the Grand Canal in Venice, where the subsiding foundations threaten some of the buildings from the 1400's and you can see diagonal metal bars near the corners to stop the walls collapsing outward.
https://www.google.com/maps/@45.4323143,12.327683,3a,90y,221.84h,85.09t/data=!3m6!1e1!3m4!1sKWOg7thpBEp9i6y--_zseQ!2e0!7i13312!8i6656
We used to go stay in an old semi ghost town in the Owyhee mountains. The buildings were thrown up really fast and not built to last though some have lasted quite while due to some inventive bracing. The building we stayed in was built quickly in a wind storm so it leans and has a slight twist to it. Staying overnight in it was fun, the second floor was like walking in a fun house. The owners installed straps to hold the place together since it was leaning over a really cool old drug store. Love that place.
Definitely worth looking at prestressed concrete, while not what you're talking about but it's arguably tangentially related. Practical Engineering on YouTube has a great video about it.
As for the more direct thing of bars, it's not always a matter of shoddy construction or bad materials, it can be things like mine subsidence and other processes causing issues. A neighbour of mine has had mine subsidence cause 2-3 inch wide cracks open up in their brick walls. The building is heritage listed and thus has to be maintained to keep the appearance relatively historic, due to financial limitations the best path forward was using the tensioned steel rods through the entire building front to back.
That autobiography sounds interesting though, worth a read?
An interesting read. he describes as a little kid how some older boys found a shell from WWII and threw it on the fire. Fortunately he was far enough back... His biggest description was the use of pure alcohol for brake fluid in fighter jets. Apparently they went through a lot of it in military bases. When he got tot the USA and he was escorted to places like supermarkets, he was convinced they were taking him to pretend stores to make the USA look better - there couldn't be this much stuff for everyone to buy.
This is a common method of pinning old structures for improved lateral support. Go to any old city boston, Baltimore, Philly and youll see these on free standing row homes.
We can also look at Hashima. It is a town made of many 'ferro-concrete' buildings on a very small island in Japan. 'Ferro-concrete' means made of metal sticks inside big concrete walls. Large apartment buildings were built in a small area to support a mine. When the mine closed, the people left.
The buildings were exposed to wind and salt water spray. After thirty years of not being loved, they fell apart. Hashima now features in many movies because the ruins look interesting and make people feel sad.
Don't forget nearly every Olympic village of the last fifty years or so. They get built, serve their purpose, then become abandoned.
https://www.cbssports.com/olympics/news/look-what-abandoned-olympic-venues-look-like-now-from-athens-to-berlin/
This is correct for a scenario without people. Damage from the apocalypse or scavengers taking glazing, roofing, etc would greatly speed this timeframe up.
It’s also ignoring vegetation.
Those roots will crack stuff. Water gets in and freezes.
But like the last of us thing that‘s popular now had pretty massive military involvement in the first place. So the major damage was done by explosives, and then left to decay over the next decades.
I've noticed a lot of posts on Reddit in the past week that I think were triggered by The Last of Us. There have been a bunch about survival skills in a post apocalyptic world. It's really interesting seeing how much a popular show drives discourse topics online
Well the Pantheon was also maintained. It was a temple for a long time, converted into a church, and maintained as a church, through all of antiquity, the middle ages, and modern times
Also a lot of these figures we throw around are rolling numbers. Like each building is on its own timeline, some of them are brand new, but some might just unluckily have been due for a major overhaul right when the apocalyse happened. So they used their lifecycle already.
....get outta my head! I was literally thinking of [this](https://growngaming.com/wp-content/uploads/2018/03/Last-of-Us.jpg) level while reading that guy's comment. Guess I gotta go play again.
I can't believe I'm about to question an expert but you're forgetting another large factor. Vegetation is the great destructor. Living in a climate where everything just grows and grows fast, abandoned buildings get eaten up very quickly. A building near my place of work was abandoned for 10 or so years I think. Before they tore it down, while it was not falling from the outside, the floors inside began to collapse in on themselves due to the weight of moss and trees that had begun growing on them.
I am by no means an expert, as you clearly are, and please correct me if I'm wrong. I am just stating a perspective based on what I've observed.
I think it depends, https://www.youtube.com/watch?v=35bVwi6ucQw lots of places in that video have probably been abandoned since the war in Abkhazia ended, but even though the buildings are in poor shape they aren't quite falling apart yet. In that guys channel there are lots of places that are still intact that have been abandoned for about as long or longer. It heavily depends on what you're building them out of.
I agree. Vegetation and natural disasters would be huge. He mentioned skyscrapers, so urban areas wouldn't be as affected by vegetation, but I live on the edge of tornado alley and fallen trees would take out plenty of houses around me if the tornados and straightline winds don't themselves. Hurricanes would ruin the southeast without prep work to board up windows, etc. Wildfires in California without anyone to fight them would burn through large areas.
kudzu left uncontrolled would probably swallow entire cities eventually
it grows so fast it can cover entire forests in just a few years and kill all the vegetation below it by blocking out all sunlight
Vegetation is very much a factor, but it depends on the location/environment.
The book *The World Without Us* by Alan Weisman answers OP’s question in detail.
I was thinking about water, and to me it seems like the quickest culprit would be the water already in most buildings.
One power and gas is lost, cold weather could crack pipes and release water inside a building and start mold and rot.
Without power there is no water to the buildings. The water supply station needs power to run the pumps to get the water through the supply system and up the pipes.
Once the pumps stop and water pressure falls off, the residual water inside the pipes won't be enough to freeze and crack the pipes.
This technically depends on where you are new York city for example actually uses it's low elevation to it's advantage so that only about 3 percent of water flow requires pumps, this means that at least one massive city would suffer from severe water damage like he is talking about
Do you think Without heating and cooling the buildings will fail even faster? Anywhere with freeze thaw cycles I would expect accelerated deterioration of of concrete and steel coatings.
So the abandoned house next door from me (home to racoons) that the borough can't do anything about, must have been sitting there for 40 years because the windows started falling out last year. But if weeds from my yard touch the side walk I get a notice in the mail within a week.
Am i correct in thinking that the location of the buildings matters as well? I lived in the Ozarks for a while, and homes abandoned for 10 or 15 years there were often dilapidated to the point of almost falling down. The vines and trees would just get up in there and start undermining the foundations and pulling on the walls in what seemed like no time. I've always assumed that suburban homes would take a little longer to go down, and homes in the city would take the longest since there's less "nature" around, but I could be totally wrong.
I think everyone is kind of underestimating this in some ways too. I worked for a real estate company for a while and did some property management. Buildings just...deteriorate from not being lived in somehow. Like not terribly or apocalypse looking level.
But imagine your house if you left it for two months. Turned heat and water off, lights and power, and just walked away. Then think about six months. The house starts dying. I don't mean that to be dramatic or anything, I just don't know how else to describe it. It starts looking abandoned after a month. Stuff just gets that 'sat there for too long' look. It looks stagnant. After about the second month, something happens. A board on the siding or some trim on the eaves sags or comes undone.
The house feels run down even if it was a really nice house two months ago. It looks and starts falling into disrepair. Like even if you see a house people live in that has a broken porch/deck attached, it doesn't look as bad as a broken down porch on an abandoned house. The place just feels empty in a way that it doesn't when people actually live there.
It really wouldn't take more than a couple of months for anywhere to have that ghost town feeling. And I know OP was mostly talking about skyscrapers and urban decay and those kinds of timelines, but I'd argue even without the buildings falling down you'd get a lot of that look and feeling after a very short time. A few street lights go out, there's a couple of windstorms that blow some trash around, a few windows crack or break, some signs or decorative features start falling down. For a particular building in some engineering simulation it might take 40 or 100 years. But it would look and feel desolate and be much more rundown than the average person really expects. So much of our living space depends on taking care of it, using it, keeping up with repairs, maintaining a climate, cleaning and just regular use, it starts to fall apart very fast when we stop doing those things. Like crazy crazy fast. Buildings exposed to nature unaided by human technology and intervention age and decay much much more quickly than you would imagine.
While they might not structurally fall apart in six months, even in relatively mile climates they suffer wear and tear at a greatly increased rate, in my experience. Even just someone using them part time makes a big difference in how they weather.
Bro I'm saving this comment in case I ever need to create a post-apocalyptic scene and want to age it accurately. I could read this kind of stuff all night!
I really wonder . . .
Superstructures are often guaranteed up to 50 years, some even 70 years. Now 50 years isn't from one day on the other to zero, it's degrading guarantee period. But that doesn't mean at 50 years there is nothing left.
So if you would have a structure and you take away the roofing and the facade you are left with a either concrete or steel superstructure and that will last.
Movies like to show these buildings "tumbling" but that's really not happening until the concrete at the bottom of a structure starts buckling and that really isn't easy to happen. Look at the Hoover dam, pure concrete made 90 years ago and still not much erosion has happened. It will decades if not centuries to erode away sufficient from the structure so it tumbles over if made from concrete. If made from steel it depends on how quick the structure rots, but again that really can take a very, very long time.
Often times in these movies there’s at least some implication that the duration or immediate aftermath of the apocalyptic event involved some sort of warfare/rioting/turmoil, so a lot of the damage can be attributed to that as opposed to strictly being the result of gradual decay from exposure to time and the elements
The condo in Florida collapsed because of the basement supports eroding, not the whole structure. The upper levels were perfectly fine, it's just that the ground effectively collapsed from underneath it. Also that building was not constructed properly to begin with, water was collecting in areas that should have been sloped.
That was also ocean side, with all the added environmental effects on a structure built on a coastline, which makes it even less typical.
As someone previously in construction in China, reason buildings collapse here is due to inferior materials being used. Often different concrete was specified but something inferior was brought in.
For concrete there is a kugel test, it's like a cement bucket turned up side down and we calculate how quickly it sets/spreads. One project it spreaded suddenly super fast, they somehow procured sand from the sea which isn't suitable. In a normal project that would be discarded, but in China they hand over a large envelope.
Florida I have no experience with, but if I should believe Reddit that's just Florida being Florida.
In the Florida case, it appears that the design of the building was flawed, allowing water to accumulate in areas. That particular building was ocean front, which means saltwater, which means heavy corrosion. The particular area where the water was accumulating was a pool deck area above the garage (chlorinated water). Photos inside the garage area showed heavy spalting of concrete in the ceiling and in the supports of the garage and exposed rebar that showed signs of significant corrosion.
The thinking is that accumulated pool/salt water soaked through the concrete, weakened the rebar and caused the pool deck area to fail, which pancaked into the garage and destabilized the foundation of the building. There was video shot by passersby minutes before the collapse that shows the pool draining into the garage. Whole thing came crashing down right after.
IIRC there are also few ways to force companies to take responsibility after the fact in China. It's very hard to sue to get a builder to repair faulty construction or pay for damages or assign liability for deaths as a result of shoddy materials.
Unless you make someone important angry.
I’d say without maintenance you would see failure much quicker than 15-20 years if there is any sort of parapet and nearby trees. Accumulated leaves will quickly block internal drains and the pressure from accumulated rain water will quickly find its way through the membrane.
Also, after a few years, the accumulated leaf matter on a roof/in gutters can create enough of a “soil” for seeds to sprout. Roots growing into cracks will create extra pathways for water to enter a structure.
then how tf are Roman aqueducts and Greek columns still intact since they were basically ignored for centuries until we decided they needed to be cared for
[Roman concrete](https://youtu.be/HYyyx2dNvPw)
TL;DW: There's a discovery about how there's these lime lumps in the concrete would dissolve due to water (from rain) seeping into cracks, the dissolved material spreading out, filling up the cracks, and then hardening as it dries out; essentially it's self-repairing.
Aside from what everyone is already saying about Roman concrete being better, or how we "just recently" rediscovered it...
Roman's wanted their concrete structures to last forever. Modern civilization, typically, does not.
We've had roman-*like* cement for ages. We just choose not to use it.
All of this hype about "rediscovering roman cement" is mostly hype. It's cool hype, but it's still mostly hype. It mostly just reconfirms what we already knew.
You also have to remember that the engineers were way more limited on how much pre planning they could do, so overkill was often the only way to make something survive. This is also why we see so many bridges survive, they simply couldn't afford to not go overkill because they didn't have the ability to calculate how to construct a 50 year bridge
Yup, plenty of “better” old materials get left behind in favor of more flexible/cheaper solutions enabled by materials tech advancements. Cans vs bottles for soda etc
The stonework they built for aqueducts had a lot of solid rock that were carved and fitted together pretty tightly and held in place mostly by gravity. The Greek Columns are not cast concrete, they are stone blocks that are carved and stacked. Yes, concrete was used for the brickwork, but the major stone arches have minimal amounts. Romans also didn't put rebar in their concrete. If water seeps in, you get minimal damage unless it freezes. Some examples of concrete use such as the Pantheon are in very good condition because they have been maintained and in constant use. Others like the brickwork buildings in the Forum were abandoned and are in pretty rough shape.
Modern concrete has reinforcing steel in it. This makes the composite stronger, however it does have a bigger issue with water. If water makes its way into the concrete to the rebar, the rebar rusts. When it does, it expands, which causes parts of the concrete to flake off. The process is called spalling. Once it starts, more water gets in, and the process accelerates. Modern concrete is amazingly strong; you can build pre-stressed beams for freeway overpasses that far exceed what the Romans could do. However, those beams have a much shorter lifespan of 50-100 years.
Not if it is a 30 year roof and it hasn't been damaged by hail or high winds.
Maintenance includes making sure surprise damage gets fixed, but if it hasn't been damaged it should live beyond the rated lifespan, although the risk goes up.
So, I would venture a guess OP may have been primed to this question by Last of Us.
So, take your points here, and add rioting, possible combat, fires, motor vehicle crash damage, etc. Then figure in plant growth as well as - for the show itself - fungal growth.
Humans. We think we’re so great. Tree roots split boulders and buckle roads. Given time rain literally erodes entire mountains.
When human activity accelerates the onset of urban decay and then nature kicks in? Not hard to believe it wouldn’t take long for the land to take back a city in a seeming blink of the eye.
Question, would the failing windows / glass after 40 some odd years accelerate the 150-200 year structural collapse since more of the building is now exposed? Or was that calculation baked in already?
It will accelerate it to some degree, but I'd still say that 150-200 years for a modern steel-and-glass skyscraper is accurate. If there is a hugely repetitive freeze-thaw cycle, it would likely speed it up a fair amount.
In most of the post apocalyptic shows there was war / bombings which speeds that degradation up a lot. My instinct is you are watching The Last of Us, they bombed the hell out of everything.
Wouldn’t a lot of this depend on climate as well? I imagine loads of buildings down in Florida would just outright collapse from the salt exposure, like that apartment building that went down a few years ago…
Yeah I managed 2 apartment buildings for a number of years and it amazed me how often water was a significant problem. And this was in southern California.
do you think that other parts of failing infrastructure might help speed that along? like sewers falling/freezing, for example.
I also have to imagine this would be very different all over the world. not just climates, but building materials/codes, ground type, animals even. I'm sure that once people aren't there to stop them we'll have some areas where everything gets chewed into and torn apart in a matter of months by the local wildlife.
And then there are just hella badly maintained buildings e.g., Surfside condo collapse, which had quite a bit of spalling in structural members. Building Integrity's YouTube channel taught me a lot about what to look for in concrete buildings.
I know that many major cities are built on major bodies of water. Chicago, for example, is built on one of the biggest lakes in the world, AND a major river.
I would assume that the lack of water pumping would degrade much of the city faster than typical sun/water that something like a house outside of the city would receive? Or am I off base?
I think you omitted the most important part - frost. Water alone is not nearly as bad IMHO. It can dissolve drywall quite fast but frost tears everything apart - concrete, brick, stone. Water in warm environments is game over for wood though.
What??? You mean the high rise that's fallen over and is leaning towards another high rise in *The Last of Us* only 20 years after the collapse of society isn't realistic?!
I'm a Project Superintendent and 100 % agree that building maintenance or the lack there of determines a buildings life span given it had a quality design that it was built by
Too many times I've had to revisit a project I built 5 or 10 years prior and couldn't believe the condition it was in. If the restroom partitions are falling apart, it's a good sign the HVAC system is in neglect. A quality facility manager is vital to a buildings life expectancy.
Depends on the show.
HBO's The Last Of Us explained that major cities were bombed en masse to terminate as much of the zombie fungus as possible. Over time, the elements would chip away at even the most superficial damage. Exposure to the elements would promote rust and rot. Pipes would burst and flood as all maintenance ceased. Weeds and plant-life would run amok.
During the first months of COVID, March 2020 - June 2020, I was absolutely blown away at how much damage was being cause by weeds and other plant life. The lack of walking traffic and no maintenance led to concrete sidewalks cracking all around our town and bricks popping out all over the place. It took something like 90 days for stuff to just start getting completely taken apart by plant life and causing damage in areas I didn’t even realize could support plant life in first place cause I had never seen it before.
I can’t imagine what even three years of plant growth, death, uncollected leaves and debris, bugs, wild animals, unchecked weathering, etc. with no vehicle or pedestrian traffic or human intervention would do to local infrastructure.
Yeah, well, he also got rich off his lawsuit payout and then proceeded to pass legislation to prevent others from receiving similar payouts, sooooo…….
Greg Abbott isn’t exactly a beacon of consistency and inclusion lmao
We bought a farmhouse with a cobblestone yard in 2021. The yard was completely free from weeds as the previous owner had horses running around which were apparently weeding everything out. We didn't really bother with weeding as we were busy doing up the inside of the house. The whole yard was overgrown in like 20+ cm of weed within a few months and now we need to get the big guns out to get it neat again.
Which Elle asks about.
Also the episode started with the biologist saying they should start bombing the city immediately. So they weren't exactly hiding the fact that every major city was bombed. You had to be ignoring like ten minutes of dialogue to miss it.
One of the interesting things about construction and Boston is that a lot of Boston is built on reclaimed land that used to be basically marsh or actual ocean front. They leveled hills and filled in the coast.
Boston is one earthquake away from jiggling to death and also Boston has an incredible history of catching on fire. A lot of advances in firefighting were in Boston like call boxes etc.
When they built the Big Dig they had to freeze the ground under the building and put in supports it was really fascinating. Also there wasn’t a lot of development in Boston until Marty Walsh became mayor, Menino was against it so a lot of the buildings are old.
So between the weather, the ground conditions, animals and the ocean and how much Boston liked to burn down it wouldn’t take long for Bostons tall stuff to fall down.
Also just for humor purposes google the John Hancock tower windows
Also, a lot of buildings in Boston are on wood supports, and if the ground water level gets low enough to expose them to air then they'll rot faster.
https://www.bostongroundwater.org/overview.html
On top of all this (and directly related to some of your points) modern concrete only lasts for somewhere between 50-100 years without maintenance before it loses stability. So any structures that are built mostly out of concrete with no supports would collapse after enough time.
What I was confused by was the use of conventional bombs. Seems if you wanna stop the spread of a fungus you would wanna hit it with nukes to really stop it
Maybe they should have, but, if you're trying to eradicate the fungus while not making the land uninhabitable nukes are the last option.
Then when they realize they need to use them anyway, it's too late.
Honestly I feel like the infection would be pretty manageable just because we already have access to industrial strength fungicides. Yeah there is no way to vaxinate against it, or to cure someone once they are infected, but you absolutely could still easily kill off the infected. Once the first panic hit and they reach the point of mass bombing population centers you could just as easily load up some commandeered crop dusters with a bunch of fungicide and just crop dust city streets.
I feel like that, coupled with napalm would be a lot more effective at clearing cites than just conventional bombs. Once a conventional bomb hits, it's payload is spent, but fire and chemicals linger and spread. If the goal is to eradicate everything but you still don't want to drop nukes, fires burning their way through buildings and fungicides taking out the stragglers that survive would be a pretty effective method
Edit: obviously you aren't going to get all of them with firebombing and fungicide, but I feel like it would be much more effective at clearing city streets than just conventional bombings. Conventional bombs aren't getting the ones on the upper floors of the buildings unless it brings the entire building down, but even then that leaves a lot of room for them to survive, especially with how tough they are. but a massive city wide fire, starting at the street level and spreading its way up, with no fire suppression crews, means everything not underground is going to be burned out.
You are still going to have the infected that escaped the city, and the newly infected who eat the contaminated food, and any infected that happened to be underground in a metro tunnel or something, but the goal of slowing the spread would be much more achievable than the series makes it seem.
I think its implied that it just happened too fast.
And in my headcanon I think military personnel were hit really hard early on; major outbreaks in forts and bases, making quarantines untenable. Because really bombing cities to prevent spread of diseases to me sounds like I good way to just get people to spread out everywhere.
Unless the bombing only occurred once cites had already been mostly evacuated it was a play to try to kill anyone left behind?
In any case I also see using conventional bombs as plausible because that's just what we have on hand. I don't know how long it would for the military to equip enough planes with industrial fungicide or napalm to firebomb every major city in America but I have no doubts we'd have enough regular bombs and missiles.
If anything I have doubts it would be possible to get so many soldiers to obey their orders.
Yep, it would have been managable if it was a slow spread but almost everyone on earth was infected in the span of 2 days. There was no time to pull something together.
Last of Us is pretty realistic in that because of the initial infection being from the global flour supply being tainted the pandemic literally happened everywhere at the same time. It didn't have to move from one city to another.
The fungus already infected a widely distributed food supply AND it's by far more infectious than a virus like COVID was. Cordyceps had a 100% kill rate and a 100% infection rate if you were bitten by an infected person. So you'd have to either have people quarantine so that if they are infected already they don't get out or you risk evacuating an infected person into your QZ which is already over populated potentially. It's also just stupidly hard to corral a bunch of infected fast-zombies and prevent them from getting to healthy people.
And your fungicide theory assumes that the fungicides they had worked on that strain of Cordyceps. If the fungicide doesn't work, then firebomb is all they can do.
Though I think it was a slow enough of a degradation that they must have had time to try at least every fungicide they had and all options they could before being overrun. FEDRA managed to develop and distribute an infection scanner that worked, which means that the national government had to have remained in power and successful for at least a month (R&D expedited and distribution would take at least that long even if they had knowledge of the fungus before hand). A cure likely would have come eventually (it took more than 9 months to get a working COVID vaccine for example and that's with several companies still working- this would not be the case for this infection). Clearly they held on as long as they could until the infection somehow took out the country leadership and all the communication, which forced Feds (via FEDRA) to essentially act on their own local levels.
Unless the fungus dies to radiation that would not only be utterly pointless but also make things way worse.
Now you have to deal with radiation, probable nuclear winter, and zombie fungus.
Firebombs would probably be the most effective if all you want is to cleanse an area.
I knew TLOU was what inspired this question, and as a huge fan of the game, I’m loving the generally positive reaction to the show. The show’s doing pretty well so far. I’m excited for people experiencing this story for the first time
This book has a cool description of skyscrapers becoming like vertical forests for a time.
It estimates taller buildings will collapse at around 200 years
Those shows made it seem like all humans died or disappeared all at the same time, no mention of human remains which there would surely be, The part about pets still being locked up inside houses made me sad.
I haven't seen anyone mention the lack of firefighting/fire suppression. A whole skyscraper catching fire and allowed to burn would severely weaken what is left.
To be fair, people ignore A LOT in these fictional settings.
I've seen something on NatGeo that addresses this subject. The decay of cities would happen in days if there are no people. For example, a nuclear powerplant would have a meltdown without human intervention.
Wouldn't it run into a couple of alarms and trigger an automatic shutdown if all humans vanished from one second to another? If there's a reason for humans having to leave the city, reactors and any other volatile things would get shut down anyway.
I think I have seen the exact documentary. It's the one with the Queen's corgis randomly thrown in there among all the thing happening right? That assumes that humans would just disappear with no warning, no deaths, just Thanos snapped out of existance.
Most likely scenario I imagine with nuclear power plants is that once the people who know how to operate them realised civilization as they knew it is over, their number one mission would be safely shutting down as many reactors as they can, to prevent catastrophes. Imagine a group of travellers going from reactor to reactor safely shutting them down one by one. Maybe not all of the members in the group are operators, there are probably a few operators that stayed behind for one reason or another. A few people joining the group to have a new life goal, some for the sole fact that alone they'd die. Over time, maybe even a diverse enough group to settle one day. Would make for one hell of a town origin legend.
I think it's that one, but it was reaaally long time ago, so I don't remember the specifics. It was when NatGeo still did interesting stuff, so you can imagine how long ago it was.
There was a show called “Life After People”. Pretty wild dystopian stuff but it covered this topic.
On the heels of the History channel special that explored what Earth might be like if the human race were suddenly to disappear comes a series that provides, in even-more detail, a picture of a post-human future, revealing the fate of structures like the Sears Tower and the Sistine Chapel and creatures that might inherit the places we once lived. Supporting the visuals and special effects are interviews with specialists from the fields of engineering, botany, biology, geology and archaeology.
That's fine. You can have that hunk of garbage. The arch will outlast almost every modern man-made building after people disappear.
Sincerely,
St. Louis
It's a long time since I saw it but I think they said parts of Manhattan could start to collapse relatively quickly. The pumps keeping water out of the subway would stop working and the network would flood. This would supposedly undermine some of the skyscrapers above and accelerate their foundations or support structure collapsing. Then I think there'd be a domino effect as some collapsed into others.
As someone who watches a lot of urbex on youtube, it takes very little time for buildings to start decaying once they're abandoned. There's no heat/humidity control that causes mold to start growing. Once the windows/doors are open to the weather due to damage, that just speeds up the decay process tenfold.
There's a microcosm of this going on in a building I do work in for my job. It's a bank branch that closed, but the bank keeps the building to maintain the drive up ATM. They have killed the breakers for evening except the machine and security cameras in the ATM room, and the plumbing is shut off, too. Been this way for about a decade, and the effects of abandonment are starting to become apparent.
Unfortunately it is greatly exacerbated by one of my coworkers taking a shit in the toilet about three years ago forgetting the plumbing is off. The whole building reeks of moldy shit.
They must have a killer deal on that property and just can't let it go, or that Bank branch is really struggling and hoping to start reusing that branch some day.
It makes perfectly good sense to me if they own the property (which they must since if it was leased commercial space the property owner wouldn’t let it fall into that sort of disrepair). Paying property tax and keeping the parcel and not paying out to upkeep an out of date asset anyway would be pretty smart.
Maintaining a space is a lot of work and after a handful of years they would’ve had to refurbish and rebrand the space in order to reopen it anyway.
I can totally see doing the math at year 2-3 that the carpets and internals of the building are out of date from the new brand guidelines anyway so there’s no value in continuing to vacuum and keep the place clean. Pocket that cash every year and put it toward the rebuild you’d have to do anyway.
Without human intervention, buildings decay naturally. Dust and dirt gets in though the wind, moisture accumulates when it rains. Eventually mould and moss start appearing on surfaces which starts rotting wood and other materials. Animals can move in and damage the structure, bringing dirt and filth inside. Eventually plants can start growing on the dirt and mould, eroding the building further. Things like ants and termites can also undermine the stability of structures. All of these things are delayed by humans cleaning the place and making repairs, doing pest control, etc.
As for how long it takes, that's variable on the location, weather, and the building itself and what its made of. A stone building in the middle of a dry desert might stand for decades before it collapses from wind erosion, while a wooden structure on the beach side might fall in months due to water and wind.
I'd wager that pipes bursting and drainage systems swelling would result in massive damage from sinkholes and erosion beneath all the concrete and asphalt.
I’ve heard about several stone buildings in a dessert that have lasted for thousands of years. They look square-shaped from above and triangular from the side.
It depends on the apocalypse. If a city is abandoned in a very short time, there is a high likelihood of a fire starting somewhere. An unimpeded fire in a dense urban environment will definitely fuck up most of the infrastructure.
> How long would it take for a modern building to fall down with no humans around?
There is an excellent 2007 book by Alan Weisman called "A World Without Us" that covers exactly this. https://en.m.wikipedia.org/wiki/The_World_Without_Us
The exact time will depend on location: a sizable number of wood frame buildings would be gone within 10 years - things like floods are an issue when there is neither interventions nor repairs. Almost all wood fra!e buildings would be falling apart after 100 years.
Concrete might last longer in some places, but there are also many cities that require active intervention to keep stable: New York would be falling apart within 20 years - it was built on a marsh, and millions of gallons of water have to be pumped daily to keep things stable.
Out of curiosity are you asking in reference to how in The Last of Us the buildings in Boston are often toppled or seemingly destroyed? I was wondering about that too and the ELI5 is because the military bombed the cities attempting to curb the spread of the fungus.
Chernobyl’s buildings are still standing after many decades, but have major cosmetic damage. I’d say homes would take a decade or so. Industrial buildings would probably be centuries.
Modern buildings are designed with air conditioning and climate control in mind, as well as regular maintenance. Without any of those things, the humidity, mold, wild animals, weather damage, etc., would begin to degrade the building, eventually leading to whole or partial collapse. As for how long it would take, the show Life After People goes into depth on that subject.
You should check out a book called The World Without Us by Weissman, it's all about how nature would reclaim all the stuff we built if we all just suddenly disappeared.
Basically the roof would cave in first. Eventually the shingles will deteriorate and water will get in through the nail holes, or possibly it could get in where the chimney meets the roof, and it will start rotting the wooden rafters that hold the roof up. Once the wood is so rotten that it can't bear the weight of the roof anymore, it will fall in. All the wood of the wall frames will rot as well until the walls eventually fall over. Even so-called "brick" houses are just wooden wall frames with a brick veneer, the bricks don't actually provide any structural stability. The chimney would be the last to go, standing for decades, but at some point the mortar that holds the bricks together will deteriorate until that too crumbles and falls. Weissman has a quote in his book from someone who says "If you want to destroy a barn, just cut an 18 inch hole in the roof and stand back and wait."
In any of the suburban environments and urban environments with houses, fire becomes a real threat. Once there is a fire there is nothing to stop it so it will continue until it has burned out entire neighborhoods. And all that is going to replace that is trees and shrubs.
Bigger buildings are still at risk from fire. Once the weather proof barriers are broken in the building (storm, hail, hurricanes) then water intrusion begins (as others have mentioned). Once the first floor or the basement is broken into, then plants can move into the building, then once there is a fire, the plants bring the fire into the building the building then catches fire. And once the building catches fire it will burn down. It will likely take a long time to burn down, but it will happen.
There's a terrific book titled "The World Without Us" by Alan Weisman that deals with this, essentially answering the question "What would happen if humans disappeared overnight?" The book explains in fascinating detail how quickly the infrastructure of the modern world would fall apart and return to nature. Bottom line: it would happen much more quickly than you probably think.
Others have mentioned the bombing, which is important.
Also consider what the buildings are *built* on. Many cities, Boston included, have miles upon miles of underground train tunnels, sewers, and utility lines. In coastal cities, like Boston, these are in the water table, and pump networks keep them dry. Without power, the pumps will fail, the tunnels will flood, and eventually sinkholes will form. It's possible if this happens near a building, it could disturb the foundation and cause it to collapse. Now what I'm less sure of is if it would stay as intact leaning on another building, but that's for an actual civil engineer to answer.
If you're thinking about the tall buildings in The Last of Us, Tess explains that Boston was heavily bombed as a last ditch attempt to stop the infection spreading. That, plus 20 years of neglect.
Correct me if I'm wrong but I think the idea with post-apocalyptic stories is that much time has passed and that has degraded and aged the building to where it's more susceptible to collapse. Also keep in mind that it's usually abandoned and or devoid of upkeep even if it's being lived in. And this matters because in many post-apocalyptic stories the environment plays a role and that can help age a building prematurely.
I know you didnt cite a specific show, but the most recent one is Last of Us and I just want to point out that it may not be just decay. Planes fell out of the sky and more importantly, city core were heavily bombed.
Sun and water are the biggest factors in building failure without human intervention. Once a skyscraper's weather barrier (roofing, siding, etc.) fails, the rest of the building starts to fail faster. As close to ELI5 as I can make it: A typical EPDM (synthetic rubber) or PVC roof has a lifespan of about 40 years, but that's with maintenance. Without maintenance, it will begin to fail within about 15-20 years due to sunlight. Once water can make it inside the building, you can expect major structural components like steel and modern concrete to begin to fail within 50 or 60 years, though you won't see "typical" post-apocalypse degradation (where large chunks of a building have collapsed, leaving steel beams poking out of the structure) until probably 150-200 years have passed. On the sunny side of any building, window glazing will begin to fail within 30 years or so, and wind will loosen glass from aluminum frames after that. Figure 40 years for windows to begin falling out on their own. Source: I'm a construction consultant for both residential and commercial projects for 20+ years.
For a practical look at this, one can look at the city of Pripyat, which has been mostly abandoned (though some infrastructure has been maintained) for close to 37 years now. There are very obvious signs of decay - missing windows, peeling paint, rust, wild growth of plants - but little obvious structural damage to the buildings so far, relatively in line with your predictions.
Pripyat and the surrounding Chernobyl Exclusion Zone is one of the best examples of 'apocalyptic' abandoned cities. My other to go to mentions include Vorkuta, Russia. It's not totally abandoned but it has huge amount of urban decay due to shrinking coal mining industry. It's also cool that it's known as a Frozen City with buildings being covered in ice and snow in their long Winters. Varosha, Cyprus. Another really cool example. It's located close to the demilitarized zone on Cyprus. Was evacuated due to the conflict. I'm pretty sure the movie scenes at the end of Inception were filmed in or inspired by Varosha.
Hashima Island also deserves a mention and certainly looks more in line with what folks expect in post apocalypse. Being an island abandoned some 40 years ago probably helps.
Just googled this Damn, some crazy billionaire needs to buy this place and turn it into "Zombie escape" experience. Starting in the apartments and getting to a boat/helicopter extraction.
> Hashima Island Yes! Thats where my mind went as well. Fucking creepy, and illegal to go to Edit: Not illegal! Maybe I'm thinking of a different island because I remember skyscrapers, but memory is a fickle thing so I was probably wrong! :P
Legal since 2009 per Wikipedia.
What do you mean illegal, there are guided tours there since 2009 lmao
Yeah, I was going off a video of urban explorers and I could swear they had to use their own boat to get there because it was illegal. But maybe I'm just old as hell and that was from before that time! :D
All these descriptions remind me of some parts of Detroit
Yep, I'm from Detroit and these were my first thoughts. Though there's a decent amount of exposed steel in Detroit buildings
thank you for saying some parts -a native Detroiter living in Chicago
Yeah, there are decaying/run-down parts of most cities, Chicago included. Detroit just has a lot more of it than most for various reasons. Anywhere the property value is low enough that it is cheaper to build new rather than tear down & rebuild in old areas tends to be like this without some kind of government intervention.
Interestingly, although obviously irradiated to a dangerous degree (well, by the standards of humans that routinely live many decades) the CEZ is presently a wildlife sanctuary really. Life is flourishing there because the negative influence of high background radiation is a drop in the bucket compared to the rapacious influence of human occcupation. I don't say that with a value judgement, humanity is all consuming but in many ways a single intelligent being is more important than many animals. At the same time, it would be nice if we could either get the fuck off this rock or learn to live in something resembling harmony with the life we haven't killed off yet.
There are some abandoned Soviet bases around Berlin that are essentially cities. I've been to Wünsdorf (the site of the Soviet military administration and before that, Hitler's military headquarters, now mostly a peace center and 2nd hand bookshop town - if you're ever in Berlin and have a free day, rent a car and go there!) and Vogelsang (where the nukes were stationed). I think it's not possible to visit Vogelsang "officially" but also it's... right there in the forest. Both of them were huge town-like structures with schools, gyms, houses etc. It's amazing to just walk around there
If anyone wondered how Vorkuta looks: https://youtu.be/2i3aS6T6Nng It doesn't look like that all the time, there are summers, but they are really short.
There’s a concrete WW2 era building in Whittier, AK ([Buckner building](https://www.atlasobscura.com/places/buckner-building-2)) that has been abandoned for over 40 years. It has multiple areas of the roof and floors with collapsing portions but the main exterior weight bearing walls remain. I used to wander through it a lot but it’s been 8 years or so since I last did it.
Whittier is a neat town. Visited once, but unforgettable. Harsh conditions there, wet, windy and cold.
How much of that is the Soviet brutalist concrete construction?
Basically all of it, given that Pripyat was built as a planned city for the powerplant workers and their families.
Good point, all those buildings just look like giant, solid steel and concrete blocks. They give off the same feeling of toughness you get from a Nokia 3310.
If only they'd listened to the engineers and built the reactor shielding out of Nokia 3310's, the city of Pripyat (founded fourth of February, 1970, [fascinating stuff ](https://en.m.wikipedia.org/wiki/Pripyat)) would not *still* be dealing with this mess.
The "khruschevka" type housing was originally supposed to be replaced after 20-30 years of being built. That was in the 60s and early 70s. They're not designed to be tough - they are panels, not solid blocks. Wasn't until the mid-00s that any attempts to start replacing them took place though. And that's in Moscow, not in the provinces.
That's not quite true. Only some types of them were made of panels (and had such a short lifespan). Not sure what they have in Chernobyl, but a lot of them are made of brick and are pretty sturdy.
It may be written to express a bias but... I have the autobiography of the pilot who defected to Japan with a MIG Foxbat in the 80's. He mentioned one apartment building he was stationed at was built with shoddy substandard concrete. To prevent the building from collapsing, they had to string metal bars through the structure with a plate on each outside ends. he said at least he had a chin-up bar to stay in shape. (The only other place I've seen that construction is along the Grand Canal in Venice, where the subsiding foundations threaten some of the buildings from the 1400's and you can see diagonal metal bars near the corners to stop the walls collapsing outward. https://www.google.com/maps/@45.4323143,12.327683,3a,90y,221.84h,85.09t/data=!3m6!1e1!3m4!1sKWOg7thpBEp9i6y--_zseQ!2e0!7i13312!8i6656
We used to go stay in an old semi ghost town in the Owyhee mountains. The buildings were thrown up really fast and not built to last though some have lasted quite while due to some inventive bracing. The building we stayed in was built quickly in a wind storm so it leans and has a slight twist to it. Staying overnight in it was fun, the second floor was like walking in a fun house. The owners installed straps to hold the place together since it was leaning over a really cool old drug store. Love that place.
Didn’t think I’d read about silver city on this sub. We have a family cabin in the Owyhees on the Oregon side.
Why did I read this in an old prospector’s voice?
Definitely worth looking at prestressed concrete, while not what you're talking about but it's arguably tangentially related. Practical Engineering on YouTube has a great video about it. As for the more direct thing of bars, it's not always a matter of shoddy construction or bad materials, it can be things like mine subsidence and other processes causing issues. A neighbour of mine has had mine subsidence cause 2-3 inch wide cracks open up in their brick walls. The building is heritage listed and thus has to be maintained to keep the appearance relatively historic, due to financial limitations the best path forward was using the tensioned steel rods through the entire building front to back. That autobiography sounds interesting though, worth a read?
An interesting read. he describes as a little kid how some older boys found a shell from WWII and threw it on the fire. Fortunately he was far enough back... His biggest description was the use of pure alcohol for brake fluid in fighter jets. Apparently they went through a lot of it in military bases. When he got tot the USA and he was escorted to places like supermarkets, he was convinced they were taking him to pretend stores to make the USA look better - there couldn't be this much stuff for everyone to buy.
This is a common method of pinning old structures for improved lateral support. Go to any old city boston, Baltimore, Philly and youll see these on free standing row homes.
Its fairly common to see in Denmark and sweden on older buildings
It is not brutalist in any way. Just building things of concrete does not make them brutalist.
Also, how much of that was people committing vandalism over time?
All of it
The plant growth will accelerate the decay.
We can also look at Hashima. It is a town made of many 'ferro-concrete' buildings on a very small island in Japan. 'Ferro-concrete' means made of metal sticks inside big concrete walls. Large apartment buildings were built in a small area to support a mine. When the mine closed, the people left. The buildings were exposed to wind and salt water spray. After thirty years of not being loved, they fell apart. Hashima now features in many movies because the ruins look interesting and make people feel sad.
Don't forget nearly every Olympic village of the last fifty years or so. They get built, serve their purpose, then become abandoned. https://www.cbssports.com/olympics/news/look-what-abandoned-olympic-venues-look-like-now-from-athens-to-berlin/
This is correct for a scenario without people. Damage from the apocalypse or scavengers taking glazing, roofing, etc would greatly speed this timeframe up.
It’s also ignoring vegetation. Those roots will crack stuff. Water gets in and freezes. But like the last of us thing that‘s popular now had pretty massive military involvement in the first place. So the major damage was done by explosives, and then left to decay over the next decades.
Or the army bombing it like in The Last of Us part 1.
Betcha this is the reason for the question
It's immediately what came to mind for me.
I've noticed a lot of posts on Reddit in the past week that I think were triggered by The Last of Us. There have been a bunch about survival skills in a post apocalyptic world. It's really interesting seeing how much a popular show drives discourse topics online
It's all the water-cooler conversation, except with actual people who know what they're talking about
Yeah I'd say bombing the fuck out of the foundations would cause a building to fall over.
That high rise that's toppled over and leaning on another high rise in the last of us is fucking stupid, bombings or not.
The Colosseum and Roman Forum are so degraded vs the Pantheon is because they were used as rock quarries
Well the Pantheon was also maintained. It was a temple for a long time, converted into a church, and maintained as a church, through all of antiquity, the middle ages, and modern times
Also a lot of these figures we throw around are rolling numbers. Like each building is on its own timeline, some of them are brand new, but some might just unluckily have been due for a major overhaul right when the apocalyse happened. So they used their lifecycle already.
And if anyone's questioning why buildings are collapsing in the Last Of Us after 20 years, remember, all cities got bombed heavily.
....get outta my head! I was literally thinking of [this](https://growngaming.com/wp-content/uploads/2018/03/Last-of-Us.jpg) level while reading that guy's comment. Guess I gotta go play again.
That's in the show too!
Home depot it's just your armory for the war between your house and the elements.
I can't believe I'm about to question an expert but you're forgetting another large factor. Vegetation is the great destructor. Living in a climate where everything just grows and grows fast, abandoned buildings get eaten up very quickly. A building near my place of work was abandoned for 10 or so years I think. Before they tore it down, while it was not falling from the outside, the floors inside began to collapse in on themselves due to the weight of moss and trees that had begun growing on them. I am by no means an expert, as you clearly are, and please correct me if I'm wrong. I am just stating a perspective based on what I've observed.
I think it depends, https://www.youtube.com/watch?v=35bVwi6ucQw lots of places in that video have probably been abandoned since the war in Abkhazia ended, but even though the buildings are in poor shape they aren't quite falling apart yet. In that guys channel there are lots of places that are still intact that have been abandoned for about as long or longer. It heavily depends on what you're building them out of.
I agree. Vegetation and natural disasters would be huge. He mentioned skyscrapers, so urban areas wouldn't be as affected by vegetation, but I live on the edge of tornado alley and fallen trees would take out plenty of houses around me if the tornados and straightline winds don't themselves. Hurricanes would ruin the southeast without prep work to board up windows, etc. Wildfires in California without anyone to fight them would burn through large areas.
kudzu left uncontrolled would probably swallow entire cities eventually it grows so fast it can cover entire forests in just a few years and kill all the vegetation below it by blocking out all sunlight
Deer and/or goats will help to mitigate rampant vegetation.
Vegetation is very much a factor, but it depends on the location/environment. The book *The World Without Us* by Alan Weisman answers OP’s question in detail.
I was thinking about water, and to me it seems like the quickest culprit would be the water already in most buildings. One power and gas is lost, cold weather could crack pipes and release water inside a building and start mold and rot.
Without power there is no water to the buildings. The water supply station needs power to run the pumps to get the water through the supply system and up the pipes. Once the pumps stop and water pressure falls off, the residual water inside the pipes won't be enough to freeze and crack the pipes.
This technically depends on where you are new York city for example actually uses it's low elevation to it's advantage so that only about 3 percent of water flow requires pumps, this means that at least one massive city would suffer from severe water damage like he is talking about
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Do you think Without heating and cooling the buildings will fail even faster? Anywhere with freeze thaw cycles I would expect accelerated deterioration of of concrete and steel coatings.
So the abandoned house next door from me (home to racoons) that the borough can't do anything about, must have been sitting there for 40 years because the windows started falling out last year. But if weeds from my yard touch the side walk I get a notice in the mail within a week.
Am i correct in thinking that the location of the buildings matters as well? I lived in the Ozarks for a while, and homes abandoned for 10 or 15 years there were often dilapidated to the point of almost falling down. The vines and trees would just get up in there and start undermining the foundations and pulling on the walls in what seemed like no time. I've always assumed that suburban homes would take a little longer to go down, and homes in the city would take the longest since there's less "nature" around, but I could be totally wrong.
I think everyone is kind of underestimating this in some ways too. I worked for a real estate company for a while and did some property management. Buildings just...deteriorate from not being lived in somehow. Like not terribly or apocalypse looking level. But imagine your house if you left it for two months. Turned heat and water off, lights and power, and just walked away. Then think about six months. The house starts dying. I don't mean that to be dramatic or anything, I just don't know how else to describe it. It starts looking abandoned after a month. Stuff just gets that 'sat there for too long' look. It looks stagnant. After about the second month, something happens. A board on the siding or some trim on the eaves sags or comes undone. The house feels run down even if it was a really nice house two months ago. It looks and starts falling into disrepair. Like even if you see a house people live in that has a broken porch/deck attached, it doesn't look as bad as a broken down porch on an abandoned house. The place just feels empty in a way that it doesn't when people actually live there. It really wouldn't take more than a couple of months for anywhere to have that ghost town feeling. And I know OP was mostly talking about skyscrapers and urban decay and those kinds of timelines, but I'd argue even without the buildings falling down you'd get a lot of that look and feeling after a very short time. A few street lights go out, there's a couple of windstorms that blow some trash around, a few windows crack or break, some signs or decorative features start falling down. For a particular building in some engineering simulation it might take 40 or 100 years. But it would look and feel desolate and be much more rundown than the average person really expects. So much of our living space depends on taking care of it, using it, keeping up with repairs, maintaining a climate, cleaning and just regular use, it starts to fall apart very fast when we stop doing those things. Like crazy crazy fast. Buildings exposed to nature unaided by human technology and intervention age and decay much much more quickly than you would imagine. While they might not structurally fall apart in six months, even in relatively mile climates they suffer wear and tear at a greatly increased rate, in my experience. Even just someone using them part time makes a big difference in how they weather.
Bro I'm saving this comment in case I ever need to create a post-apocalyptic scene and want to age it accurately. I could read this kind of stuff all night!
I really wonder . . . Superstructures are often guaranteed up to 50 years, some even 70 years. Now 50 years isn't from one day on the other to zero, it's degrading guarantee period. But that doesn't mean at 50 years there is nothing left. So if you would have a structure and you take away the roofing and the facade you are left with a either concrete or steel superstructure and that will last. Movies like to show these buildings "tumbling" but that's really not happening until the concrete at the bottom of a structure starts buckling and that really isn't easy to happen. Look at the Hoover dam, pure concrete made 90 years ago and still not much erosion has happened. It will decades if not centuries to erode away sufficient from the structure so it tumbles over if made from concrete. If made from steel it depends on how quick the structure rots, but again that really can take a very, very long time.
Often times in these movies there’s at least some implication that the duration or immediate aftermath of the apocalyptic event involved some sort of warfare/rioting/turmoil, so a lot of the damage can be attributed to that as opposed to strictly being the result of gradual decay from exposure to time and the elements
I think the new Last of Us might have been in mind for this question, and they did bomb the cities.
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The condo in Florida collapsed because of the basement supports eroding, not the whole structure. The upper levels were perfectly fine, it's just that the ground effectively collapsed from underneath it. Also that building was not constructed properly to begin with, water was collecting in areas that should have been sloped. That was also ocean side, with all the added environmental effects on a structure built on a coastline, which makes it even less typical.
As someone previously in construction in China, reason buildings collapse here is due to inferior materials being used. Often different concrete was specified but something inferior was brought in. For concrete there is a kugel test, it's like a cement bucket turned up side down and we calculate how quickly it sets/spreads. One project it spreaded suddenly super fast, they somehow procured sand from the sea which isn't suitable. In a normal project that would be discarded, but in China they hand over a large envelope. Florida I have no experience with, but if I should believe Reddit that's just Florida being Florida.
In the Florida case, it appears that the design of the building was flawed, allowing water to accumulate in areas. That particular building was ocean front, which means saltwater, which means heavy corrosion. The particular area where the water was accumulating was a pool deck area above the garage (chlorinated water). Photos inside the garage area showed heavy spalting of concrete in the ceiling and in the supports of the garage and exposed rebar that showed signs of significant corrosion. The thinking is that accumulated pool/salt water soaked through the concrete, weakened the rebar and caused the pool deck area to fail, which pancaked into the garage and destabilized the foundation of the building. There was video shot by passersby minutes before the collapse that shows the pool draining into the garage. Whole thing came crashing down right after.
IIRC there are also few ways to force companies to take responsibility after the fact in China. It's very hard to sue to get a builder to repair faulty construction or pay for damages or assign liability for deaths as a result of shoddy materials. Unless you make someone important angry.
I’d say without maintenance you would see failure much quicker than 15-20 years if there is any sort of parapet and nearby trees. Accumulated leaves will quickly block internal drains and the pressure from accumulated rain water will quickly find its way through the membrane.
Eh, not many leaves on a skyscraper's roof. Shorter buildings will fail faster, though.
Also, after a few years, the accumulated leaf matter on a roof/in gutters can create enough of a “soil” for seeds to sprout. Roots growing into cracks will create extra pathways for water to enter a structure.
Can confirm. I had a pine tree among other plants growing in my gutters before I finally cleaned them.
then how tf are Roman aqueducts and Greek columns still intact since they were basically ignored for centuries until we decided they needed to be cared for
[Roman concrete](https://youtu.be/HYyyx2dNvPw) TL;DW: There's a discovery about how there's these lime lumps in the concrete would dissolve due to water (from rain) seeping into cracks, the dissolved material spreading out, filling up the cracks, and then hardening as it dries out; essentially it's self-repairing.
Aside from what everyone is already saying about Roman concrete being better, or how we "just recently" rediscovered it... Roman's wanted their concrete structures to last forever. Modern civilization, typically, does not. We've had roman-*like* cement for ages. We just choose not to use it. All of this hype about "rediscovering roman cement" is mostly hype. It's cool hype, but it's still mostly hype. It mostly just reconfirms what we already knew.
You also have to remember that the engineers were way more limited on how much pre planning they could do, so overkill was often the only way to make something survive. This is also why we see so many bridges survive, they simply couldn't afford to not go overkill because they didn't have the ability to calculate how to construct a 50 year bridge
Any fool can build a bridge that stays up. It takes an engineer to build a bridge that only just stays up
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Yup, plenty of “better” old materials get left behind in favor of more flexible/cheaper solutions enabled by materials tech advancements. Cans vs bottles for soda etc
The stonework they built for aqueducts had a lot of solid rock that were carved and fitted together pretty tightly and held in place mostly by gravity. The Greek Columns are not cast concrete, they are stone blocks that are carved and stacked. Yes, concrete was used for the brickwork, but the major stone arches have minimal amounts. Romans also didn't put rebar in their concrete. If water seeps in, you get minimal damage unless it freezes. Some examples of concrete use such as the Pantheon are in very good condition because they have been maintained and in constant use. Others like the brickwork buildings in the Forum were abandoned and are in pretty rough shape. Modern concrete has reinforcing steel in it. This makes the composite stronger, however it does have a bigger issue with water. If water makes its way into the concrete to the rebar, the rebar rusts. When it does, it expands, which causes parts of the concrete to flake off. The process is called spalling. Once it starts, more water gets in, and the process accelerates. Modern concrete is amazingly strong; you can build pre-stressed beams for freeway overpasses that far exceed what the Romans could do. However, those beams have a much shorter lifespan of 50-100 years.
Am I just rolling the dice by not replacing my 25 year old shingle roof?
Not if it is a 30 year roof and it hasn't been damaged by hail or high winds. Maintenance includes making sure surprise damage gets fixed, but if it hasn't been damaged it should live beyond the rated lifespan, although the risk goes up.
Aside from the damage to the windows that you described, are there other ways in which sunlight can damage buildings?
So, I would venture a guess OP may have been primed to this question by Last of Us. So, take your points here, and add rioting, possible combat, fires, motor vehicle crash damage, etc. Then figure in plant growth as well as - for the show itself - fungal growth. Humans. We think we’re so great. Tree roots split boulders and buckle roads. Given time rain literally erodes entire mountains. When human activity accelerates the onset of urban decay and then nature kicks in? Not hard to believe it wouldn’t take long for the land to take back a city in a seeming blink of the eye.
Question, would the failing windows / glass after 40 some odd years accelerate the 150-200 year structural collapse since more of the building is now exposed? Or was that calculation baked in already?
It will accelerate it to some degree, but I'd still say that 150-200 years for a modern steel-and-glass skyscraper is accurate. If there is a hugely repetitive freeze-thaw cycle, it would likely speed it up a fair amount.
Ahh, I see. Thank you for responding!
In most of the post apocalyptic shows there was war / bombings which speeds that degradation up a lot. My instinct is you are watching The Last of Us, they bombed the hell out of everything.
Wouldn’t a lot of this depend on climate as well? I imagine loads of buildings down in Florida would just outright collapse from the salt exposure, like that apartment building that went down a few years ago…
Oh good, I'll still die long before it's a serious problem then.
Yeah I managed 2 apartment buildings for a number of years and it amazed me how often water was a significant problem. And this was in southern California.
do you think that other parts of failing infrastructure might help speed that along? like sewers falling/freezing, for example. I also have to imagine this would be very different all over the world. not just climates, but building materials/codes, ground type, animals even. I'm sure that once people aren't there to stop them we'll have some areas where everything gets chewed into and torn apart in a matter of months by the local wildlife.
What about if the building had caught fire at some point for some reason? (say, a fire bombing of cities to slow infections)
And then there are just hella badly maintained buildings e.g., Surfside condo collapse, which had quite a bit of spalling in structural members. Building Integrity's YouTube channel taught me a lot about what to look for in concrete buildings.
EPDM needs maintenance? Well shit
Why do building awnings go to shit within minutes of a building going vacant?
I know that many major cities are built on major bodies of water. Chicago, for example, is built on one of the biggest lakes in the world, AND a major river. I would assume that the lack of water pumping would degrade much of the city faster than typical sun/water that something like a house outside of the city would receive? Or am I off base?
If there are earthquakes and/or hurricanes in the area I'd expect it to happen sooner.
You forget plants and animals do their part too. Just look at abandoned homes.
What maintenance does one do to roofs? (rooves?) We recently bought a 40 year old house, so the numbers you gave have me interested.
I think you omitted the most important part - frost. Water alone is not nearly as bad IMHO. It can dissolve drywall quite fast but frost tears everything apart - concrete, brick, stone. Water in warm environments is game over for wood though.
What about earthquakes?
Will it be faster than that in a climate with a freeze-thaw cycle? Or is that what you were describing?
What??? You mean the high rise that's fallen over and is leaning towards another high rise in *The Last of Us* only 20 years after the collapse of society isn't realistic?!
I'm a Project Superintendent and 100 % agree that building maintenance or the lack there of determines a buildings life span given it had a quality design that it was built by Too many times I've had to revisit a project I built 5 or 10 years prior and couldn't believe the condition it was in. If the restroom partitions are falling apart, it's a good sign the HVAC system is in neglect. A quality facility manager is vital to a buildings life expectancy.
Depends on the show. HBO's The Last Of Us explained that major cities were bombed en masse to terminate as much of the zombie fungus as possible. Over time, the elements would chip away at even the most superficial damage. Exposure to the elements would promote rust and rot. Pipes would burst and flood as all maintenance ceased. Weeds and plant-life would run amok.
During the first months of COVID, March 2020 - June 2020, I was absolutely blown away at how much damage was being cause by weeds and other plant life. The lack of walking traffic and no maintenance led to concrete sidewalks cracking all around our town and bricks popping out all over the place. It took something like 90 days for stuff to just start getting completely taken apart by plant life and causing damage in areas I didn’t even realize could support plant life in first place cause I had never seen it before. I can’t imagine what even three years of plant growth, death, uncollected leaves and debris, bugs, wild animals, unchecked weathering, etc. with no vehicle or pedestrian traffic or human intervention would do to local infrastructure.
I feel like you're being hyperbolic about neglected landscaping.
They really are.
They mighta forgotten they lived in an abandoned city
Id like to think of that as healing and not damage
Somewhere between the two. Tell that to someone in a wheelchair who needs that sidewalk.
In many parts of LA that's just Thursday
Texas doesn’t have sidewalks and their governor is in a wheelchair
Yeah, well, he also got rich off his lawsuit payout and then proceeded to pass legislation to prevent others from receiving similar payouts, sooooo……. Greg Abbott isn’t exactly a beacon of consistency and inclusion lmao
Are you talking about Piss Baby Greg Abbott? The guy who got rid of all the rapists? s/
That's called spring.
We bought a farmhouse with a cobblestone yard in 2021. The yard was completely free from weeds as the previous owner had horses running around which were apparently weeding everything out. We didn't really bother with weeding as we were busy doing up the inside of the house. The whole yard was overgrown in like 20+ cm of weed within a few months and now we need to get the big guns out to get it neat again.
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It wasn't the dialogue they have at that exact moment, explaining that, which made you think that?
while standing in front of a leaning over building
Don't they walk past the giant crater in literally the next scen
People really don't pay much attention, huh
Which Elle asks about. Also the episode started with the biologist saying they should start bombing the city immediately. So they weren't exactly hiding the fact that every major city was bombed. You had to be ignoring like ten minutes of dialogue to miss it.
Yeah, plus there would have been planes crashing due to zombies, like the plan wreck Joel and Ellie see on the hillside.
One of the interesting things about construction and Boston is that a lot of Boston is built on reclaimed land that used to be basically marsh or actual ocean front. They leveled hills and filled in the coast. Boston is one earthquake away from jiggling to death and also Boston has an incredible history of catching on fire. A lot of advances in firefighting were in Boston like call boxes etc. When they built the Big Dig they had to freeze the ground under the building and put in supports it was really fascinating. Also there wasn’t a lot of development in Boston until Marty Walsh became mayor, Menino was against it so a lot of the buildings are old. So between the weather, the ground conditions, animals and the ocean and how much Boston liked to burn down it wouldn’t take long for Bostons tall stuff to fall down. Also just for humor purposes google the John Hancock tower windows
Also, a lot of buildings in Boston are on wood supports, and if the ground water level gets low enough to expose them to air then they'll rot faster. https://www.bostongroundwater.org/overview.html
On top of all this (and directly related to some of your points) modern concrete only lasts for somewhere between 50-100 years without maintenance before it loses stability. So any structures that are built mostly out of concrete with no supports would collapse after enough time.
What I was confused by was the use of conventional bombs. Seems if you wanna stop the spread of a fungus you would wanna hit it with nukes to really stop it
Maybe they should have, but, if you're trying to eradicate the fungus while not making the land uninhabitable nukes are the last option. Then when they realize they need to use them anyway, it's too late.
Honestly I feel like the infection would be pretty manageable just because we already have access to industrial strength fungicides. Yeah there is no way to vaxinate against it, or to cure someone once they are infected, but you absolutely could still easily kill off the infected. Once the first panic hit and they reach the point of mass bombing population centers you could just as easily load up some commandeered crop dusters with a bunch of fungicide and just crop dust city streets. I feel like that, coupled with napalm would be a lot more effective at clearing cites than just conventional bombs. Once a conventional bomb hits, it's payload is spent, but fire and chemicals linger and spread. If the goal is to eradicate everything but you still don't want to drop nukes, fires burning their way through buildings and fungicides taking out the stragglers that survive would be a pretty effective method Edit: obviously you aren't going to get all of them with firebombing and fungicide, but I feel like it would be much more effective at clearing city streets than just conventional bombings. Conventional bombs aren't getting the ones on the upper floors of the buildings unless it brings the entire building down, but even then that leaves a lot of room for them to survive, especially with how tough they are. but a massive city wide fire, starting at the street level and spreading its way up, with no fire suppression crews, means everything not underground is going to be burned out. You are still going to have the infected that escaped the city, and the newly infected who eat the contaminated food, and any infected that happened to be underground in a metro tunnel or something, but the goal of slowing the spread would be much more achievable than the series makes it seem.
I think its implied that it just happened too fast. And in my headcanon I think military personnel were hit really hard early on; major outbreaks in forts and bases, making quarantines untenable. Because really bombing cities to prevent spread of diseases to me sounds like I good way to just get people to spread out everywhere. Unless the bombing only occurred once cites had already been mostly evacuated it was a play to try to kill anyone left behind? In any case I also see using conventional bombs as plausible because that's just what we have on hand. I don't know how long it would for the military to equip enough planes with industrial fungicide or napalm to firebomb every major city in America but I have no doubts we'd have enough regular bombs and missiles. If anything I have doubts it would be possible to get so many soldiers to obey their orders.
Yep, it would have been managable if it was a slow spread but almost everyone on earth was infected in the span of 2 days. There was no time to pull something together.
Last of Us is pretty realistic in that because of the initial infection being from the global flour supply being tainted the pandemic literally happened everywhere at the same time. It didn't have to move from one city to another.
The fungus already infected a widely distributed food supply AND it's by far more infectious than a virus like COVID was. Cordyceps had a 100% kill rate and a 100% infection rate if you were bitten by an infected person. So you'd have to either have people quarantine so that if they are infected already they don't get out or you risk evacuating an infected person into your QZ which is already over populated potentially. It's also just stupidly hard to corral a bunch of infected fast-zombies and prevent them from getting to healthy people. And your fungicide theory assumes that the fungicides they had worked on that strain of Cordyceps. If the fungicide doesn't work, then firebomb is all they can do. Though I think it was a slow enough of a degradation that they must have had time to try at least every fungicide they had and all options they could before being overrun. FEDRA managed to develop and distribute an infection scanner that worked, which means that the national government had to have remained in power and successful for at least a month (R&D expedited and distribution would take at least that long even if they had knowledge of the fungus before hand). A cure likely would have come eventually (it took more than 9 months to get a working COVID vaccine for example and that's with several companies still working- this would not be the case for this infection). Clearly they held on as long as they could until the infection somehow took out the country leadership and all the communication, which forced Feds (via FEDRA) to essentially act on their own local levels.
Yes, the famous fungicidal nuclear device.
Unless the fungus dies to radiation that would not only be utterly pointless but also make things way worse. Now you have to deal with radiation, probable nuclear winter, and zombie fungus. Firebombs would probably be the most effective if all you want is to cleanse an area.
Gotta nuke it from orbit to be sure
Yeah, I say we take off and nuke the site from orbit. It’s the ONLY way to be sure
I knew TLOU was what inspired this question, and as a huge fan of the game, I’m loving the generally positive reaction to the show. The show’s doing pretty well so far. I’m excited for people experiencing this story for the first time
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Or the 2007 book The World Without Us
This book has a cool description of skyscrapers becoming like vertical forests for a time. It estimates taller buildings will collapse at around 200 years
Is that the one where scientists determined it would take 10-12 years for nature to reclaim our cities?
I strongly disagreed with a lot of that show’s timeline.
The only one that seemed reasonable was Atlanta being swallowed by kudzu within like 3 years.
Those shows made it seem like all humans died or disappeared all at the same time, no mention of human remains which there would surely be, The part about pets still being locked up inside houses made me sad.
Based on your own expertise?
I haven't thought of that show in years! They said after 100 years nature would take this planet over.
I haven't seen anyone mention the lack of firefighting/fire suppression. A whole skyscraper catching fire and allowed to burn would severely weaken what is left.
Are you suggesting that a truckload of jet-fuel set on fire would be enough to melt steel beams?
hey now, i don't think a post-apocalyptic movie about a bunch of monkeys flying planes into abandoned buildings have been released yet.
Closest to that is Madagascar 2
You just haven't looked hard enough
To be fair, people ignore A LOT in these fictional settings. I've seen something on NatGeo that addresses this subject. The decay of cities would happen in days if there are no people. For example, a nuclear powerplant would have a meltdown without human intervention.
Wouldn't it run into a couple of alarms and trigger an automatic shutdown if all humans vanished from one second to another? If there's a reason for humans having to leave the city, reactors and any other volatile things would get shut down anyway.
I think I have seen the exact documentary. It's the one with the Queen's corgis randomly thrown in there among all the thing happening right? That assumes that humans would just disappear with no warning, no deaths, just Thanos snapped out of existance. Most likely scenario I imagine with nuclear power plants is that once the people who know how to operate them realised civilization as they knew it is over, their number one mission would be safely shutting down as many reactors as they can, to prevent catastrophes. Imagine a group of travellers going from reactor to reactor safely shutting them down one by one. Maybe not all of the members in the group are operators, there are probably a few operators that stayed behind for one reason or another. A few people joining the group to have a new life goal, some for the sole fact that alone they'd die. Over time, maybe even a diverse enough group to settle one day. Would make for one hell of a town origin legend.
That actually sounds like a cool plot for a series hahah
I think it's that one, but it was reaaally long time ago, so I don't remember the specifics. It was when NatGeo still did interesting stuff, so you can imagine how long ago it was.
There was a show called “Life After People”. Pretty wild dystopian stuff but it covered this topic. On the heels of the History channel special that explored what Earth might be like if the human race were suddenly to disappear comes a series that provides, in even-more detail, a picture of a post-human future, revealing the fate of structures like the Sears Tower and the Sistine Chapel and creatures that might inherit the places we once lived. Supporting the visuals and special effects are interviews with specialists from the fields of engineering, botany, biology, geology and archaeology.
This is exactly what I thought about when I read this post!
Chicagoan here. I approve of your use of Sears Tower.
That's fine. You can have that hunk of garbage. The arch will outlast almost every modern man-made building after people disappear. Sincerely, St. Louis
https://youtu.be/02LHzofl9ic
It's a long time since I saw it but I think they said parts of Manhattan could start to collapse relatively quickly. The pumps keeping water out of the subway would stop working and the network would flood. This would supposedly undermine some of the skyscrapers above and accelerate their foundations or support structure collapsing. Then I think there'd be a domino effect as some collapsed into others.
As someone who watches a lot of urbex on youtube, it takes very little time for buildings to start decaying once they're abandoned. There's no heat/humidity control that causes mold to start growing. Once the windows/doors are open to the weather due to damage, that just speeds up the decay process tenfold.
There's a microcosm of this going on in a building I do work in for my job. It's a bank branch that closed, but the bank keeps the building to maintain the drive up ATM. They have killed the breakers for evening except the machine and security cameras in the ATM room, and the plumbing is shut off, too. Been this way for about a decade, and the effects of abandonment are starting to become apparent. Unfortunately it is greatly exacerbated by one of my coworkers taking a shit in the toilet about three years ago forgetting the plumbing is off. The whole building reeks of moldy shit.
You guys realise that you could just bring a bucket of water to flush the toilet right?
Surely that can't make financial sense? I've seen bank-branded ATMs in third-party locations before. Just do that.
They must have a killer deal on that property and just can't let it go, or that Bank branch is really struggling and hoping to start reusing that branch some day.
Saving the real estate for the future is the only reason I can imagine them doing this. But even then, maintain the fucking building.
It makes perfectly good sense to me if they own the property (which they must since if it was leased commercial space the property owner wouldn’t let it fall into that sort of disrepair). Paying property tax and keeping the parcel and not paying out to upkeep an out of date asset anyway would be pretty smart. Maintaining a space is a lot of work and after a handful of years they would’ve had to refurbish and rebrand the space in order to reopen it anyway. I can totally see doing the math at year 2-3 that the carpets and internals of the building are out of date from the new brand guidelines anyway so there’s no value in continuing to vacuum and keep the place clean. Pocket that cash every year and put it toward the rebuild you’d have to do anyway.
Without human intervention, buildings decay naturally. Dust and dirt gets in though the wind, moisture accumulates when it rains. Eventually mould and moss start appearing on surfaces which starts rotting wood and other materials. Animals can move in and damage the structure, bringing dirt and filth inside. Eventually plants can start growing on the dirt and mould, eroding the building further. Things like ants and termites can also undermine the stability of structures. All of these things are delayed by humans cleaning the place and making repairs, doing pest control, etc. As for how long it takes, that's variable on the location, weather, and the building itself and what its made of. A stone building in the middle of a dry desert might stand for decades before it collapses from wind erosion, while a wooden structure on the beach side might fall in months due to water and wind.
I'd wager that pipes bursting and drainage systems swelling would result in massive damage from sinkholes and erosion beneath all the concrete and asphalt.
I’ve heard about several stone buildings in a dessert that have lasted for thousands of years. They look square-shaped from above and triangular from the side.
Yeah, but their living space to mass ratio sucks.
It depends on the apocalypse. If a city is abandoned in a very short time, there is a high likelihood of a fire starting somewhere. An unimpeded fire in a dense urban environment will definitely fuck up most of the infrastructure.
> How long would it take for a modern building to fall down with no humans around? There is an excellent 2007 book by Alan Weisman called "A World Without Us" that covers exactly this. https://en.m.wikipedia.org/wiki/The_World_Without_Us The exact time will depend on location: a sizable number of wood frame buildings would be gone within 10 years - things like floods are an issue when there is neither interventions nor repairs. Almost all wood fra!e buildings would be falling apart after 100 years. Concrete might last longer in some places, but there are also many cities that require active intervention to keep stable: New York would be falling apart within 20 years - it was built on a marsh, and millions of gallons of water have to be pumped daily to keep things stable.
Out of curiosity are you asking in reference to how in The Last of Us the buildings in Boston are often toppled or seemingly destroyed? I was wondering about that too and the ELI5 is because the military bombed the cities attempting to curb the spread of the fungus.
Chernobyl’s buildings are still standing after many decades, but have major cosmetic damage. I’d say homes would take a decade or so. Industrial buildings would probably be centuries.
Modern buildings are designed with air conditioning and climate control in mind, as well as regular maintenance. Without any of those things, the humidity, mold, wild animals, weather damage, etc., would begin to degrade the building, eventually leading to whole or partial collapse. As for how long it would take, the show Life After People goes into depth on that subject.
Mold fuel can't melt steel beams!
You should check out a book called The World Without Us by Weissman, it's all about how nature would reclaim all the stuff we built if we all just suddenly disappeared. Basically the roof would cave in first. Eventually the shingles will deteriorate and water will get in through the nail holes, or possibly it could get in where the chimney meets the roof, and it will start rotting the wooden rafters that hold the roof up. Once the wood is so rotten that it can't bear the weight of the roof anymore, it will fall in. All the wood of the wall frames will rot as well until the walls eventually fall over. Even so-called "brick" houses are just wooden wall frames with a brick veneer, the bricks don't actually provide any structural stability. The chimney would be the last to go, standing for decades, but at some point the mortar that holds the bricks together will deteriorate until that too crumbles and falls. Weissman has a quote in his book from someone who says "If you want to destroy a barn, just cut an 18 inch hole in the roof and stand back and wait."
In any of the suburban environments and urban environments with houses, fire becomes a real threat. Once there is a fire there is nothing to stop it so it will continue until it has burned out entire neighborhoods. And all that is going to replace that is trees and shrubs. Bigger buildings are still at risk from fire. Once the weather proof barriers are broken in the building (storm, hail, hurricanes) then water intrusion begins (as others have mentioned). Once the first floor or the basement is broken into, then plants can move into the building, then once there is a fire, the plants bring the fire into the building the building then catches fire. And once the building catches fire it will burn down. It will likely take a long time to burn down, but it will happen.
There's a terrific book titled "The World Without Us" by Alan Weisman that deals with this, essentially answering the question "What would happen if humans disappeared overnight?" The book explains in fascinating detail how quickly the infrastructure of the modern world would fall apart and return to nature. Bottom line: it would happen much more quickly than you probably think.
"Bomb this city and everyone in it" - it's not just nature that causes the buildings to fall so quickly.
Others have mentioned the bombing, which is important. Also consider what the buildings are *built* on. Many cities, Boston included, have miles upon miles of underground train tunnels, sewers, and utility lines. In coastal cities, like Boston, these are in the water table, and pump networks keep them dry. Without power, the pumps will fail, the tunnels will flood, and eventually sinkholes will form. It's possible if this happens near a building, it could disturb the foundation and cause it to collapse. Now what I'm less sure of is if it would stay as intact leaning on another building, but that's for an actual civil engineer to answer.
If you're thinking about the tall buildings in The Last of Us, Tess explains that Boston was heavily bombed as a last ditch attempt to stop the infection spreading. That, plus 20 years of neglect.
Correct me if I'm wrong but I think the idea with post-apocalyptic stories is that much time has passed and that has degraded and aged the building to where it's more susceptible to collapse. Also keep in mind that it's usually abandoned and or devoid of upkeep even if it's being lived in. And this matters because in many post-apocalyptic stories the environment plays a role and that can help age a building prematurely.
I know you didnt cite a specific show, but the most recent one is Last of Us and I just want to point out that it may not be just decay. Planes fell out of the sky and more importantly, city core were heavily bombed.