Insulation Calculator

About This Calculator

Select your US climate zone, insulation location (attic, wall, floor, or crawlspace), material type, and area to insulate. The calculator returns the IECC 2021 recommended R-value for your zone, the required thickness for your chosen material, and a material quantity estimate — bags for blown-in products, coverage square footage for batt products.

How It Works

R-value targets come from IECC 2021 Table R402.1.2 by climate zone and assembly location. Thickness = recommendedR ÷ R-per-inch for the selected material. Bags needed (blown materials) = ⌈area × (thickness ÷ 3.5 in) ÷ 40 sq ft per bag⌉. Batt coverage area = ⌈area⌉ sq ft (accounting for batt format width/length). Local jurisdictions may require higher R-values than the IECC minimum.

The Formula

Frequently Asked Questions

How do I find my US climate zone?

The US Department of Energy divides the country into 8 climate zones based on heating/cooling load. Zone 1 covers Hawaii and southern Florida (hot/humid); Zone 7–8 covers Alaska and extreme northern states (very cold). Most of the contiguous US falls in Zones 3–6. A full state-by-county map is available from the DOE Building America Solution Center or the IECC 2021 publication.

What does IECC 2021 R-value mean?

IECC (International Energy Conservation Code) 2021 Table R402.1.2 specifies the minimum thermal resistance (R-value) for different building assemblies in each climate zone. These are the minimum code requirements for new residential construction — existing retrofit projects often exceed these to improve energy efficiency. The R-value in this calculator is the recommendation for the assembly location you select.

Why do some materials show bags and others show coverage area?

Blown-in materials (fiberglass blown, cellulose blown) are sold in bags rated by coverage area at a specified installed depth. The calculator converts your required thickness to an equivalent bags-at-reference-depth count. Batt and rigid board materials are sold by the roll or sheet in standard widths; the coverage area tells you how many square feet of product to purchase.

Should I always insulate to exactly the IECC minimum?

The IECC minimum is a building-code floor, not necessarily the optimum for energy savings or comfort. Many energy efficiency programs (ENERGY STAR, DOE Zero Energy Ready Home) require higher R-values. In retrofit applications, additional insulation beyond code minimum typically has a positive return through energy bill savings. Consult your local building department (authority having jurisdiction) for permit requirements.