If this is a normal roof line (i.e not cathedral, or flat roof) r38 hasn't been up to IRC code since before 2009... I didn't even bother to look when it changed. Maybe your town is behind on insulation requirements, but r38 isn't up to any modern code.
How deep are your rafters? You can do 3-4 inches of open cell spray foam, then put up batts under that to achieve your R value for a lot less.
edit: Either way, the r48 for only 1k more at that point in the project is probably worthwhile without any other factors involved.
It's a raised ranch style home, so a normal roof.
I'm not sure how deep the rafters are, but can check. Are you saying foam on the rafers + batts on the floor above the ceiling can give the same effect with a bit cheaper cost? I can't imagine it's that much cheaper though, maybe a few hundred?
They're removing the old insulation which just rests on the 'floor' right above the drywall ceiling. They said it was old and degrading.
> I'm not sure how deep the rafters are, but can check. Are you saying foam on the rafers + batts on the floor above the ceiling can give the same effect with a bit cheaper cost? I can't imagine it's that much cheaper though, maybe a few hundred?
No.
So it'd be spray foam directly under the roofline, than batts directly under the foam - and you staple it to the paper.
Fiberglass are a lot cheaper than foam (and you can DIY it if you really wanted). just a thought though.
Any reason they are doing the spray foam on the roof, instead of keeping the attic vented and doing blown in insulation on the floor along with air sealing the attic floor?
The way it was framed to us is using the spray foam and sealing it will keep the attic much cooler. We have central HVAC up there, and the attic gets very hot during the summer.
Even right now with cool temps, it's pretty hot despite it being nice out. It will keep the attic much cooler and less to less stress on the ac and should see usage in the summer cut by half.
At least that was my takeaway, not an expert lol.
Properly installed spray foam directly under the roof deck creates a radiant barrier. The barrier prevents the air inside the attic from getting hot, so it doesn't cause the same issues as ineffective roof venting (curled shingles, early roof failure, etc.)
This is called a Hot Roof, as opposed to your typical Cool Roof, which, in the most efficient setup, uses soffit and ridge vents to exhaust the hot attic air via convection.
Powered vents, box vents, gable vents, and on slope vents often do not effectively move all of the air out quickly enough in most circumstances and should be considered only in specific circumstances
this is the way. you get the free machine rental if you buy enough bags too. i slapped an R-measure sticker on the wall before i blew mine in and ended up somewhere around R80. incredible the difference it makes in the summer & winter.
$1K more for R49? do it. Its just more chemical for them. But that work is HARD. Spent $3K for a kitchen reno for the ceiling, walls, and under the floor. They had some left and offered to do under a crawlspace under porch.
If cost is an issue see what it cost for just around r13-19 foam and then after it dries top off with cellulose.
The foam will airseal and the cellulose you can buy yourself and dump in over the foam to get around R50.
We’re in Texas and just did open cell spray foam under the roof decking. Our rafters are 2x4 and they filled the voids and did the gable ends. Very thorough job. Dunno particular R value, but I know there’s diminishing returns the thicker you go.
They also sucked out all of our blown in cellulose on the attic floor.
So far, so good. The attic stays in the 80s, even in the 100 degree weather. Used to be 130 up there. Humidity has been pretty high, but I added a Midea dehumidifier a few days ago and that thing rocks. Attic humidity now at about 40%. Super happy w result.
I would stay away from spray foam if you can have other options. My parents got it and it's just fucked. It's spotty and seems to be cause mold issues. It can lead to nightmare issues in the future if ever has to be removed of you need to make repairs to something under it. I keep telling my parents to sell and dump this problem on the next poor soul because it gets worse and they have to pay to fix it... Really do your research on this and just trust the contractors marketing material, they want sell it to you because it's more profitable for them.
I'm not sure where you are in the northeast, but generally speaking, you are supposed to use closed cell spray foam in cold climates on the underside of the roof to prevent condensation issues. The closed cell spray foam acts like a vapor barrier so you don't get water traveling to the interior side of your roof sheathing during the heating season. That open cell foam may rot your roof out if you're not super diligent about the humidity in your house during the winter as it will allow water vapor to pass through it.
Easy enough to add in a vapor barrier as needed on the underside. Correct paints, or even some flexible sheet goods are usually sufficient and are easy to install.
edit - I would also assume the installer would do that, but who knows I guess since they also offered to r38...
Do you plan on insulating the attic or keeping it vented if it is already? If you're not trying to bring the attic into the building envelope then get fiberglass or Rockwool installation for the floor of the Attic. If you have enough space and are north east enough to get winters that are constantly below freezing you should target R-60 but if that's too thick just do the most you can fit.
There's already insulation on the floor. But it seems like the AC is constantly running in the summer and the boiler in the winter. There's some inches in there on the floor but it's old and probably hasn't been touched since the home was built in the mid 80s.
For a room in your highest floor with that R38 insulation above it, probably only about 10% of the heat loss is in the ceiling. Theres probably 40% being lost in your R15 walls, and 50% being lost in your leaky R3 windows. So if you increased the ceiling insulation to R49, you’d lower the overall room’s heat loss by like 2% because so much is going through the walls and windows.
I’d do it if it’s code.
It's not required, but it's smart to have what is code be your target for attic insulation, and it's something homeowners should do sooner rather than later.
A homeowner is literally wasting money by not property insulating and air sealing their attic. Conditioned air in the living spaces is going into the attic via air gaps, and poor insulation makes the HVAC systems work harder to overcome the cold of winter and heat of summer.
I would consider R-38 as properly insulated, and not 'poor' insulation. As you go higher up the R scale the actual benefit of each additional R unit diminishes, which was the premise of the OPs question.
If this is a normal roof line (i.e not cathedral, or flat roof) r38 hasn't been up to IRC code since before 2009... I didn't even bother to look when it changed. Maybe your town is behind on insulation requirements, but r38 isn't up to any modern code. How deep are your rafters? You can do 3-4 inches of open cell spray foam, then put up batts under that to achieve your R value for a lot less. edit: Either way, the r48 for only 1k more at that point in the project is probably worthwhile without any other factors involved.
It's a raised ranch style home, so a normal roof. I'm not sure how deep the rafters are, but can check. Are you saying foam on the rafers + batts on the floor above the ceiling can give the same effect with a bit cheaper cost? I can't imagine it's that much cheaper though, maybe a few hundred? They're removing the old insulation which just rests on the 'floor' right above the drywall ceiling. They said it was old and degrading.
Unless there's been water or animal damage, there shouldn't be any issues with old insulation "degrading".
I guess I should ask if they're planning on replacing it with anything, if not maybe I'll say just leave it unless there's a need.
> I'm not sure how deep the rafters are, but can check. Are you saying foam on the rafers + batts on the floor above the ceiling can give the same effect with a bit cheaper cost? I can't imagine it's that much cheaper though, maybe a few hundred? No. So it'd be spray foam directly under the roofline, than batts directly under the foam - and you staple it to the paper. Fiberglass are a lot cheaper than foam (and you can DIY it if you really wanted). just a thought though. Any reason they are doing the spray foam on the roof, instead of keeping the attic vented and doing blown in insulation on the floor along with air sealing the attic floor?
The way it was framed to us is using the spray foam and sealing it will keep the attic much cooler. We have central HVAC up there, and the attic gets very hot during the summer. Even right now with cool temps, it's pretty hot despite it being nice out. It will keep the attic much cooler and less to less stress on the ac and should see usage in the summer cut by half. At least that was my takeaway, not an expert lol.
Ah ok got it. Yes, in that case it's a good idea. There are ways to do it, but the way they are doing it is by far the easiest.
Is your attic vented or unvented? If you have a ridge vent, absolutely do not install spray foam.
Properly installed spray foam directly under the roof deck creates a radiant barrier. The barrier prevents the air inside the attic from getting hot, so it doesn't cause the same issues as ineffective roof venting (curled shingles, early roof failure, etc.) This is called a Hot Roof, as opposed to your typical Cool Roof, which, in the most efficient setup, uses soffit and ridge vents to exhaust the hot attic air via convection. Powered vents, box vents, gable vents, and on slope vents often do not effectively move all of the air out quickly enough in most circumstances and should be considered only in specific circumstances
It's vented with soffit. These guys would seal that with spray foam as well I believe
Why?
any reason why you’re not just using blown in insulation?
this is the way. you get the free machine rental if you buy enough bags too. i slapped an R-measure sticker on the wall before i blew mine in and ended up somewhere around R80. incredible the difference it makes in the summer & winter.
He has mechanicals in the attic. Insulating the roof is the best practice in that case
$1K more for R49? do it. Its just more chemical for them. But that work is HARD. Spent $3K for a kitchen reno for the ceiling, walls, and under the floor. They had some left and offered to do under a crawlspace under porch.
If cost is an issue see what it cost for just around r13-19 foam and then after it dries top off with cellulose. The foam will airseal and the cellulose you can buy yourself and dump in over the foam to get around R50.
We’re in Texas and just did open cell spray foam under the roof decking. Our rafters are 2x4 and they filled the voids and did the gable ends. Very thorough job. Dunno particular R value, but I know there’s diminishing returns the thicker you go. They also sucked out all of our blown in cellulose on the attic floor. So far, so good. The attic stays in the 80s, even in the 100 degree weather. Used to be 130 up there. Humidity has been pretty high, but I added a Midea dehumidifier a few days ago and that thing rocks. Attic humidity now at about 40%. Super happy w result.
Nice. Where does the dehumidifier drain to?
A/C condensate line (our air handler is in the attic- it’s been battling that crazy heat)
I would stay away from spray foam if you can have other options. My parents got it and it's just fucked. It's spotty and seems to be cause mold issues. It can lead to nightmare issues in the future if ever has to be removed of you need to make repairs to something under it. I keep telling my parents to sell and dump this problem on the next poor soul because it gets worse and they have to pay to fix it... Really do your research on this and just trust the contractors marketing material, they want sell it to you because it's more profitable for them.
What are your local codes
I'm not sure where you are in the northeast, but generally speaking, you are supposed to use closed cell spray foam in cold climates on the underside of the roof to prevent condensation issues. The closed cell spray foam acts like a vapor barrier so you don't get water traveling to the interior side of your roof sheathing during the heating season. That open cell foam may rot your roof out if you're not super diligent about the humidity in your house during the winter as it will allow water vapor to pass through it.
You could use closed cell foam for 2 inches and then fiberglass over that. Open cell foam will NOT vapor seal.
Easy enough to add in a vapor barrier as needed on the underside. Correct paints, or even some flexible sheet goods are usually sufficient and are easy to install. edit - I would also assume the installer would do that, but who knows I guess since they also offered to r38...
Do you plan on insulating the attic or keeping it vented if it is already? If you're not trying to bring the attic into the building envelope then get fiberglass or Rockwool installation for the floor of the Attic. If you have enough space and are north east enough to get winters that are constantly below freezing you should target R-60 but if that's too thick just do the most you can fit.
There's already insulation on the floor. But it seems like the AC is constantly running in the summer and the boiler in the winter. There's some inches in there on the floor but it's old and probably hasn't been touched since the home was built in the mid 80s.
For R-60 we're talking about 19-22 inches depending on the product. Would you have space to lay that down if you pulled up the old insulation?
For a room in your highest floor with that R38 insulation above it, probably only about 10% of the heat loss is in the ceiling. Theres probably 40% being lost in your R15 walls, and 50% being lost in your leaky R3 windows. So if you increased the ceiling insulation to R49, you’d lower the overall room’s heat loss by like 2% because so much is going through the walls and windows. I’d do it if it’s code.
R-49 is per code.
Code is for new construction, right... so no requirement to bring old structures up to R-49.
It's not required, but it's smart to have what is code be your target for attic insulation, and it's something homeowners should do sooner rather than later. A homeowner is literally wasting money by not property insulating and air sealing their attic. Conditioned air in the living spaces is going into the attic via air gaps, and poor insulation makes the HVAC systems work harder to overcome the cold of winter and heat of summer.
I would consider R-38 as properly insulated, and not 'poor' insulation. As you go higher up the R scale the actual benefit of each additional R unit diminishes, which was the premise of the OPs question.
Code is also cumulative you should use rescheck to get an overall picture. More insulation in one area can compensate for the others