Wall insulation for zone 3
Hinton308
| Posted in GBA Pro Help on
Working on details for new construction plans. My thoughts are to use Zip R sheathing on outside (to protect against thermal bridging). What R factor should I use? I plan to on inside either use Owens Corning Energy Complete That would air seal wall and then blow in insulation. OR spray 1″ closed cell foam and then use blown in cellulose. I want insulation R value to be above what is required today and build for tomorrows requirements. Looking for most cost effective use. Want to achieve a 1.5 or less ACH50 blower test. Location Spartanburg SC 29349
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An inch of closed cell foam installed between studs offers no real benefit other than air sealing in a zone 3 climate. It's expensive, and not very green. For the cost of just 1" of closed cell foam better air sealing is achieved by filling a 2x4 cavity with half-pound open cell foam, which uses slightly less polymer and only water as the blowing agent.
In Table 2 p10 of BA-1005, in the climate zone 3 row the starting point for the financial rationality discussion starts at R20 whole-wall. Going much beyond that could become a "pays never" proposition.
An example of an R20 whole wall stackup using ZIP-R would be 2x6/R20 cellulose (R13-R15, depending on framing fraction and siding options) plus 1.5" ZIP-R (R6.6). That may or may not be financially rational compared to 1" ZIP (R3.6) and a 2x6/R20 with 24" o.c. stud spacing and single-board top plates & window framing and a few other Advance Framing techniques to minimize the framing fraction.
IRC code min would be the 2x6/R20 without the insulating ZIP, just standard sheathing.
An inch of closed cell foam installed between studs offers no real benefit other than air sealing in a zone 3 climate. It's expensive, and not very green. For the cost of just 1" of closed cell foam better air sealing is achieved by filling a 2x4 cavity with half-pound open cell foam, which uses slightly less polymer and only water as the blowing agent.
In Table 2 p10 of BA-1005, in the climate zone 3 row the starting point for the financial rationality discussion starts at R20 whole-wall. Going much beyond that could become a "pays never" proposition.
https://buildingscience.com/sites/default/files/migrate/pdf/BA-1005_High%20R-Value_Walls_Case_Study.pdf
An example of an R20 whole wall stackup using ZIP-R would be 2x6/R20 cellulose (R13-R15, depending on framing fraction and siding options) plus 1.5" ZIP-R (R6.6). That may or may not be financially rational compared to 1" ZIP (R3.6) and a 2x6/R20 with 24" o.c. stud spacing and single-board top plates & window framing and a few other Advance Framing techniques to minimize the framing fraction.
IRC code min would be the 2x6/R20 without the insulating ZIP, just standard sheathing.
Thank you Dana. Planning on a 2x4 wall assembly— what would be your comments with this wall
Sincerely Don
Make sure to look at the Zip info - the shear wall aspect ratios for Zip -R are different than plywood shear walls.
Consider (inside to out) polyiso strips on the studs, cellulose or open cell foam, taped plywood sheathing, then Typar.