Thermal Envelope Calculator

R-value and continuous insulation from climate zone.

Wall area (sq ft)

Cavity insulation R-value

Continuous insulation R-value

Framing fraction (%)

Framing R-value

Design ΔT (°F)

Heating degree-days (HDD)

Energy cost ($/BTU)

Tab to move between fields

Composite wall R-value

16.18

Composite U-value

0.06

Design heat loss (BTU/hr)4,946

Annual heat loss (MMBTU)14.84

Annual energy cost ($)$445.11

Meets ASHRAE 90.1 (1=yes)1

How to Use This Calculator

Enter Total Wall Area in sq ft — opaque wall only, excluding windows and doors.
Set Cavity Insulation R-Value (e.g., R-13 for 2×4 walls) and Continuous Insulation R-Value for exterior foam or mineral wool.
Enter Framing Fraction (%) — typically 20–25% — and Framing R-Value to account for thermal bridging.
Set Design ΔT (°F) and Heating Degree-Days for your location.
Review Composite Wall R-Value, Composite U-Value, Annual Heat Loss (MMBTU), and Annual Energy Cost to evaluate insulation upgrades.

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