Roof Insulation R-Value Calculator
Estimate added insulation thickness, achievable nominal R-value, package quantity and cost for a roof or attic area using editable product performance and depth assumptions.
Default project preview
8.57 in
Added R-value needed
R-30
Depth-limited R-value
R-47
Target shortfall
R-2
Order coverage
1,320 ft²
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Added R-value = target R − existing R. Required thickness = added R ÷ product R per thickness unit. Package quantity uses roof area plus allowance.
FAQ
Roof Insulation R-Value Calculator questions
Why can the achieved R-value be below the target?+
The entered cavity or available depth may be too small for the selected product performance.
Does nominal R-value equal whole-roof performance?+
No. Framing, gaps, compression and air leakage reduce assembly performance.
Can different insulation layers be combined?+
Often yes, but vapor control, ventilation and compatibility must be designed for the roof assembly.