What R-value do I need for exterior walls?

The IRC prescriptive requirements range from R-13 (climate zone 1–3) to R-20 or R-21 (climate zones 5–8). Check the energy code for your zip code.

Fiberglass vs. mineral wool batts — which is better?

Mineral wool (Rockwool/Safe'n'Sound) is denser, better at sound control, fire resistant, and moisture resistant. Fiberglass is less expensive. Both provide similar R-values per inch.

Cavity Insulation Calculator

Calculate the number of insulation batts needed for your wall or ceiling cavities.

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Enter Your Measurements

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How to Use This Calculator

1Measure total wall or ceiling area to be insulated.
2Click Calculate.

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About This Material

Fiberglass or mineral wool batts fill the stud/joist cavities. For 2x4 walls: R-13 or R-15. For 2x6 walls: R-19 or R-21. For attic: R-38 to R-60 depending on climate zone.

Installation Tips

•Fill cavities completely — compressed or gapped insulation loses R-value.
•Do not leave gaps around electrical boxes and pipes.
•Wear a respirator when handling fiberglass batts.

Common Mistakes to Avoid

Compressing batts — compression significantly reduces R-value.
Leaving air gaps at top plates and bottom plates.
Not installing vapor retarder in cold climates.