Layering two materials? Enter the thickness of each. You get the total R-value, the RSI and the U-factor.
Your shopping list
11.2 RTotal R-value
1.97RSI (metric)
8.93 Btu/h per FHeat loss per 100 sq ft
- U-factor1 divided by R0.09
Framing lowers the R-value of a whole wall, so a real wall tests lower than this sum.
How to use the R-Value Calculator
- Pick the first material and its thickness.
- Pick the second layer, or leave it at none.
- Add extra R for drywall and air films if you want, then read the total.
The math behind it
R of a layer = thickness x R-value per inch
Total R = R1 + R2 + extra R
U-factor = 1 / total R, RSI = total R / 5.678
A worked example
What we typed in
- First layer material: Fiberglass batt (about R-3.2 per in)
- First layer thickness: 3.5 in
- Second layer material: XPS foam board (about R-5 per in)
- Second layer thickness: 1 in
- Extra R-value (drywall, air films): 0
What we got
- Total R-value: 16.2 R
- RSI (metric): 2.85
- Heat loss per 100 sq ft: 6.17 Btu/h per F
- U-factor: 0.06
Tips from the job site
- Add the R-values of layers in a row. Do not average them.
- Framing lowers the whole wall R-value, so a real wall tests lower than this sum.
Common questions
How do I add R-values?
Add them up for every layer the heat passes through in a row.
What is a U-factor?
It is 1 divided by the R-value. A lower U-factor means a better wall.
See all Insulation Calculators.