PDFWAC 51-11C-61014

Section A101.4Compression of insulation.

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
[Statutory Authority: RCW 19.27A.020, 19.27A.025 and chapters 19.27 and 34.05 RCW. WSR 13-04-056, § 51-11C-61014, filed 2/1/13, effective 7/1/13.]