Best insulation methods for framed walls, basement walls and basement slab
I am building a 1,000 sq. ft addition attached to a 1,800 sq ft house, located in Climate Zone 5, Northern Ohio, Zipcode 44685. The addition is a kitchen, laundry room and master bedroom suite to include bedroom, bath and closet. The addition will be 2” x 4” 16” OC framed 8’ foot walls with a flat insulated ceiling. Roof will be 4/12 pitch roof. The basement will be built with 12’/ 8” concrete block walls. My questions center around the framed walls, basement walls and basement slab.
Framed Walls – current design is (Inside to outside) are: drywall, 3” closed cell foam, ½” OSB sheathing, 1” XPS Rigid insulation, house wrap, and vinyl siding. Here some questions around the design?
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Since 3” closed cell will be used to insulate the 2 x 4 cavity is it correct to skip the interior poly vapor barrier?
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What options are available to replace the house wrap with a sheathing systems such as the Huber Zip System Sheathing and Tape. What is the correct sequence of installing rigid insulation board when using the the Zip system?
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What about using the Zip R sheathing to replace the OSB sheathing, rigid insulation and house wrap? What would be the correct thickness?
Basement Slab – (all below grade) current design is (inside to outside) – 4” concrete, 6 MIL. Polyethylene vapor barrier, 2” XPS Rigid insulation, 4” stone (no fines). Here some questions around the design?
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Is the 6 MIL polyethylene vapor barrier required? Will it cause a problem used in addition to the 2” XPS rigid insulation?
Basement Wall – starting from the top there is 2 feet of 8” block with facing brick and then the lower 7 feet will be 12” block. A capillary break will be installed on the top of poured concrete footing. For its insulation and waterproofing benefit current design calls for 2 ⅜” Tuff-N-Dry installed on the exterior for the below grade portion of wall. Interior of wall will have 2” XPS installed floor to ceiling.
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Is there a problem sandwiching the below grade portion of the wall with Tuff-N-Dry on the outside and the 2” XPS on the inside?
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Replies
For your walls, I'd use Membrain, cellulose and unfaced EPS. Taped sheathing and airtight drywall.
If you are going to use XPS, consider omitting the OSB (use diagonal steel strapping and tape the XPS).
Arland,
Your assemblies look good. With closed cell foam, you shouldn't need an additional vapor barrier, but that's up to your building inspector. If you go with the ZIP sheathing, after you tape the seams, you can install foam directly to the sheathing. Here's an article about installing exterior rigid foam insulation:
https://www.greenbuildingadvisor.com/article/can-vinyl-siding-be-applied-over-furring-strips
And here's some info that will be helpful when it comes to your wall assembly and siding choice:
https://www.greenbuildingadvisor.com/article/can-vinyl-siding-be-applied-over-furring-strips
Because ZIP R-Sheathing insulates inside the OSB, I don't think there would be a worry like there is with exterior foam when it comes to minimum thickness. So, as long as your cavity insulation and the insulated sheathing are meeting the code, you should be good to go. More would be better, of course.
You're basement wall and slab assemblies look good, too. And yes, you need the poly vapor barrier below the slab. Here's an article that will be helpful with the basement questions:
https://www.greenbuildingadvisor.com/article/all-about-basements
Brian,
Thanks for the quick reply. I think you've clarified things for me. After the sentence "And here's some info that will be helpful when it comes to your wall assembly and siding choice:" you've provide a duplicate link of the previous one that talks about vinyl siding over furring strips. Can you provide the link for wall assembly and siding choice?
Thanks,
Arland
Sorry about that. This was supposed to be the first link:
https://www.greenbuildingadvisor.com/article/how-to-install-rigid-foam-sheathing