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

PDFWAC 51-11C-61014

Section A101.4—Compression of insulation.