Quote:
Originally Posted by gtojohn
When I originally googled air film I got mostly results for the film "air". While at the store yesterday I did find Perma-R Poly sheathing with foil. The 3/8" board itself shows r-1.5 . And lists the system, with minimum 3/4" air gap reaching r-4.47. That could be multiplied for 3 3/8" for almost r-13.41 with a 1/8" thermal break before sheet rock on a 2x4 wall...if you could make it work within an 1/8" tolerance. The same could be done with 2 layers of their 3/4" board for 3" r-11.94 with a 1/2 space left over between sheetrock.
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Yeah, this all sounds very reasonable.
It's quite similar to the
Multi Layer Insulation idea I am investigating.
However, R13.41 total R-value in a 4" wall (really 3.5") is not so amazing.
For comparison:
- Your multi-layer foil faced Perma-R Poly is R-13.41
- Dense Packed Cellulose would give you R-12.95
- Mineral wool in that same space is R-15.
- Solid XPS would give you R-17.5
- Solid PolyIso would give you about R-22
Don't forget, that if you have a standard stud wall, the stud itself has an R-value of R-1 per inch, and is a "
thermal bridge", conducting unwanted heat or cold, so the stud section itself is actually R-3.5. In typical wall construction, the cumulative wall R-value will be reduced for any insulation by about 18%, so the above numbers would be:
- Your multi-layer foil faced Perma-R Poly is R-11
- Dense Packed Cellulose would give you R-10.62
- Mineral wool in that same space is R-12.3
- Solid XPS would give you R-14.35
- Solid PolyIso would give you about 18.04
If you can make your stud system non-continuous, it is a very large improvement.
-AC