Insulation R-Value Calculator
Calculate the total R-value of a layered wall or attic assembly, and compare it against common recommended targets.
Total assembly R-value
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Vs target —
Simple series sum; does not account for thermal bridging through framing, which lowers effective real-world R-value somewhat.
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How it works
Total R-value = sum of each layer's R-value (layers in series add directly)Frequently Asked Questions
How do I calculate total R-value?
Layers stacked in series simply add: fiberglass batts at R-13 plus rigid foam sheathing at R-5 gives a wall assembly of R-18 (before accounting for framing thermal bridging, which slightly lowers the real-world effective value).
What R-value do I need?
It varies by climate zone — attics commonly target R-38 to R-60 in cold climates, walls R-13 to R-21, and floors over unheated spaces R-25 to R-30. Check your region's building code or Energy Star recommendations for your zone.
Does higher R-value always mean better?
Up to a point — more insulation reduces heat loss with diminishing returns, and very high R-values can have longer payback periods. Air sealing gaps is often just as important as raw R-value, since air leaks bypass insulation entirely.