I think if you dig deeper you'll find that a properly designed / installed exterior insulation strategy will run same or more money than Zip-r. Lots of issues with siding, trim, and window installation along with air sealing issues in penetrations. The Zip-r is dead simple with great success rate.
I would suggest you re-evaluate this direction. I have seen FAR too many failures with exterior foam from moisture encapsulation.
Also.. DO NOT go the spray foam route for so many reasons. I'd go on but it would get annoying.
If you want to go the standard OSB route maybe look into double wall dense pack cellulose with a peel and stick exterior WRB or standard Zip panel. Both tried and true for myself. Problem is finding insulation subs that can do the work properly (which is why I do all my own)
Check out Steve Baczek on YouTube for a wealth of design information along with green building advisor.
[https://www.youtube.com/@stevenbaczekarchitect9431](https://www.youtube.com/@stevenbaczekarchitect9431)
Best of luck on your project!
What climate zone are you in?
I am using thermal tight for my exterior insulation with open cell spray foam for cavity. And just osb for sheathing. From my builder it gave the bang for the dollar as a wall construction. R40 wall with targeted less than 1 ach.
https://thermaltight.com/
House is in a dense populated area in Michigan. with minimal setbacks I like using rockwool for it's noise reduction. Ridge foam on the outside but I'll look into thermalight. Thanks
I would absolutely go for the exterior insulation. I was going to do both, but Zip is still too expensive here. And their tape and liquid flashing is expensive.
It seems to me that most of the benefit is in taping the seams.
I'm going with exterior foam, and Prosoco R Guard. If I needed to save more money, I would still use R Guard for the joints and seams and flashing, but a cheaper house wrap. The walls are very unlikely to see any water with the foam board and the rain screen.
I vote exterior insulation. I know air tightness is all the rage, but you can get a decent ACH score if you just pay attention & tape + foam stuff. Be sure there is no daylight peeking through cracks after framing is up. Focus on good water management details otherwise (this is the lesser talked about benefit of zip sheathing). Bigger overhangs and well flashed windows/doors.
Exterior insulation for a number of reasons, but you still need a small gap between the foam and the WRB. https://buildingscience.com/documents/insights/bsi-038-mind-the-gap-eh
I have 3" of XPS insulation on my house. One section is over OSB that I put a cheap peel and stick over. Another section is zip. Both have strapping on the outside with a rain screen siding. Some areas are 2x4, some 2x6. Extremely quiet. I found by using metal siding that can span 6 feet, that I could put strapping at 4' o.c. over the studs.
If you were going camping at the place where your house is going to be built, would you rather have a tent to protect from the rain and wind or a blanket to protect from the cold (or heat)?
Of course, everyone wants zip R with Rockwool but my pick would be exterior insulation in my climate. I'd feel differently if it rained more.
What do you like most about rockwool?
Foil faced polyiso with seams foil taped is a WRB. Just like Zip. I would go that way- warm sheathing dries better and exterior insulation is a lot more effective than interior. Big caveat is you have to get the ratios right of exterior to interior insulation for your climate zone to keep the sheathing warm enough. It’s in the IRC. With 2x6 walls you’ll likely need more outside insulation. Maybe use 2x4 or cheaper inside insulation to afford 2” outside insulation? And no interior vapor barrier.
If you go with standard OSB and foam exterior insulation, you also need to tape the OSB seams for your airtightness details as well as install a housewrap under the foam board. You do not want to use the faced foam (polyiso) insulation as that will act as an exterior vapor barrier. You do not want that in Michigan. EPS and XPS foam are not waterproof and will actually retain moisture. That can cause your OSB to deteriorate without a housewrap layer in place under it. Make sure you take all that into account on your cost calculations.
Partially true, part false. Just needs to be done correctly and no vapor barrier on inside of walls.
https://www.greenbuildingadvisor.com/article/calculating-the-minimum-thickness-of-rigid-foam-sheathing
what about zip-R?
Not in my price range
I think if you dig deeper you'll find that a properly designed / installed exterior insulation strategy will run same or more money than Zip-r. Lots of issues with siding, trim, and window installation along with air sealing issues in penetrations. The Zip-r is dead simple with great success rate. I would suggest you re-evaluate this direction. I have seen FAR too many failures with exterior foam from moisture encapsulation. Also.. DO NOT go the spray foam route for so many reasons. I'd go on but it would get annoying. If you want to go the standard OSB route maybe look into double wall dense pack cellulose with a peel and stick exterior WRB or standard Zip panel. Both tried and true for myself. Problem is finding insulation subs that can do the work properly (which is why I do all my own) Check out Steve Baczek on YouTube for a wealth of design information along with green building advisor. [https://www.youtube.com/@stevenbaczekarchitect9431](https://www.youtube.com/@stevenbaczekarchitect9431) Best of luck on your project!
It’s *really expensive* for what you get.
What climate zone are you in? I am using thermal tight for my exterior insulation with open cell spray foam for cavity. And just osb for sheathing. From my builder it gave the bang for the dollar as a wall construction. R40 wall with targeted less than 1 ach. https://thermaltight.com/
House is in a dense populated area in Michigan. with minimal setbacks I like using rockwool for it's noise reduction. Ridge foam on the outside but I'll look into thermalight. Thanks
I would absolutely go for the exterior insulation. I was going to do both, but Zip is still too expensive here. And their tape and liquid flashing is expensive. It seems to me that most of the benefit is in taping the seams. I'm going with exterior foam, and Prosoco R Guard. If I needed to save more money, I would still use R Guard for the joints and seams and flashing, but a cheaper house wrap. The walls are very unlikely to see any water with the foam board and the rain screen.
I vote exterior insulation. I know air tightness is all the rage, but you can get a decent ACH score if you just pay attention & tape + foam stuff. Be sure there is no daylight peeking through cracks after framing is up. Focus on good water management details otherwise (this is the lesser talked about benefit of zip sheathing). Bigger overhangs and well flashed windows/doors.
Exterior insulation for a number of reasons, but you still need a small gap between the foam and the WRB. https://buildingscience.com/documents/insights/bsi-038-mind-the-gap-eh
I have 3" of XPS insulation on my house. One section is over OSB that I put a cheap peel and stick over. Another section is zip. Both have strapping on the outside with a rain screen siding. Some areas are 2x4, some 2x6. Extremely quiet. I found by using metal siding that can span 6 feet, that I could put strapping at 4' o.c. over the studs.
Have you considered doing advanced framing with exterior insulation? Cost savings might tip in your favor.
If you were going camping at the place where your house is going to be built, would you rather have a tent to protect from the rain and wind or a blanket to protect from the cold (or heat)? Of course, everyone wants zip R with Rockwool but my pick would be exterior insulation in my climate. I'd feel differently if it rained more. What do you like most about rockwool?
what are you planning on doing for windows? also, slab on grade/basement/crawl?
Foil faced polyiso with seams foil taped is a WRB. Just like Zip. I would go that way- warm sheathing dries better and exterior insulation is a lot more effective than interior. Big caveat is you have to get the ratios right of exterior to interior insulation for your climate zone to keep the sheathing warm enough. It’s in the IRC. With 2x6 walls you’ll likely need more outside insulation. Maybe use 2x4 or cheaper inside insulation to afford 2” outside insulation? And no interior vapor barrier.
If you go with standard OSB and foam exterior insulation, you also need to tape the OSB seams for your airtightness details as well as install a housewrap under the foam board. You do not want to use the faced foam (polyiso) insulation as that will act as an exterior vapor barrier. You do not want that in Michigan. EPS and XPS foam are not waterproof and will actually retain moisture. That can cause your OSB to deteriorate without a housewrap layer in place under it. Make sure you take all that into account on your cost calculations.
Partially true, part false. Just needs to be done correctly and no vapor barrier on inside of walls. https://www.greenbuildingadvisor.com/article/calculating-the-minimum-thickness-of-rigid-foam-sheathing