Wash. Admin. Code § 51-11C-61014
A101.4 Compression of insulation. Insulation which is compressed shall be rated in accordance with Table A101.4 or reduction in value may be calculated in accordance with the procedures in the ASHRAE Fundamentals Handbook.
Table A101.4 R-value of Fiberglass Batts Compressed Within Various Depth Cavities
Insulation R-Values at Standard Thickness | |||||||||||||
Rated R-Value | 82 | 71 | 60 | 49 | 38 | 30 | 22 | 21 | 19 | 15 | 13 | 11 | |
Standard Thickness, Inches | 26.0 | 22.5 | 19.0 | 15.5 | 12 | 9.5 | 6.5 | 5.5 | 6 | 3.5 | 3.5 | 3.5 | |
Nominal Lumber Sizes, Inches | Actual Depth of Cavity, Inches | Insulation R-Values when Installed in a Confined Cavity | |||||||||||
Truss | 26.0 | 82 | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- |
Truss | 22.5 | -- | 71 | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- |
Truss | 19.0 | -- | -- | 60 | -- | -- | -- | -- | -- | -- | -- | -- | -- |
Truss | 15.5 | -- | -- | -- | 49 | -- | -- | -- | -- | -- | -- | -- | -- |
Truss | 12.0 | -- | -- | -- | -- | 38 | -- | -- | -- | -- | -- | -- | -- |
2 x 12 | 11.25 | -- | -- | -- | -- | 37 | -- | -- | -- | -- | -- | -- | -- |
2 x 10 | 9.25 | -- | -- | -- | -- | 32 | 30 | -- | -- | -- | -- | -- | -- |
2 x 8 | 7.25 | -- | -- | -- | -- | 27 | 26 | 22 | 21 | 19 | -- | -- | -- |
2 x 6 | 5.5 | -- | -- | -- | -- | -- | 21 | 20 | 21 | 18 | -- | -- | -- |
2 x 4 | 3.5 | -- | -- | -- | -- | -- | -- | 14 | -- | 13 | 15 | 13 | 11 |
2.5 | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | 9.8 | -- | |
1.5 | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | 6.3 | 6.0 | |
Wash. Admin. Code § 51-11C-61014
Statutory Authority: RCW 19.27A.020, 19.27A.025 and chapters 19.27 and 34.05 RCW. 13-04-056, § 51-11C-61014, filed 2/1/13, effective 7/1/13.