Thickness

Generally, R-value increases linearly with thickness. For example, a 2" thickness of a material will have twice the R-value of a 1" thickness of the same material. Recent advances in thermal insulation technol­ogy, however, have shown a phenomenon known as the thickness effect in low-density materials. Simply stated, the thickness effect is an

Thickness

Zone

Attic Floor (Ceilings)

Sidewalls

Floors

1

R-19

R-12

R-11

2

R-30

R-19

R-11

3

R-38

R-19

R-13

4

R-38

R-19

R-19

5

R-49

R-19

R-25

R-values on the chart represent CertairiTeed recommendations based on the latest Model Energy Code and DOE recommendations. The wall R-values include those for both insulation and sheathing. R-values of individual products can be added to achieve recommended R-values. For example, R-38 added to an R-11 results in R-49. Wall R-values include length, insulation and sheathing.

Figure 3.1 R-values. (CertairiTeed.) apparent decrease in R-value per inch with increased thickness. Many examples suggest that conduction is actually taking place, com­promising the R-value.