IECC 2021 · Walls • Foundations • Basements • Attics

Does Your Insulation
Pass Building Code?

Choose your wall type and materials from the dropdowns — the calculator assembles them in the correct code-compliant order and gives an instant pass/fail against IECC 2021.

Spray Foam Rigid Foam Mineral Wool ICF & CMU Vapor Barriers 100% Free

R-Value Calculator › Wall Assembly

Wall Assembly R-Value Check

Choose your materials — assembly is built automatically in the correct order

IECC 2021
Code standard
WALL ASSEMBLY — INTERIOR TO EXTERIOR INTERIOR EXTERIOR Choose your assembly below

Layer widths proportional to physical thickness — updates live as you choose materials

1Code Requirements

IECC minimum: R-15

2Foundation / Wall Structure
3Interior Insulation
4Vapor Barrier
5Interior Framing (optional — for added insulation)
6Interior Finish
7Exterior Insulation & Drainage (optional)

XPS rigid foam is commonly applied to the outside of foundation walls before backfilling. Dimple board goes over the XPS for drainage.

Assembled in code-compliant order
Total R-ValueR-0.0

Required: R-15 •

R-0
—
R-0Required: R-15
⚠ R-values reference IECC 2021. Nominal values — actual performance varies with installation. Always verify with your local AHJ before construction.
→ Check egress windows, stair code, ceiling heights at buildcodecalculator.com

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Code Reference

IECC 2021 Minimum R-Values by Zone

Requirements vary significantly by climate zone and assembly type. Choose your zone in the calculator above to see the exact minimum for your situation.

ZoneRegionBasement WallAbove-Grade WallAtticFloor
Zone 1Hawaii, GuamR-0R-13R-30R-13
Zone 2South FL, Gulf TXR-0R-13R-38R-13
Zone 3GA, AL, TX, CA CoastR-5R-20R-38R-19
Zone 4KY, VA, OR, WAR-10R-20R-49R-19
Zone 5OH, PA, NE, CO, ILR-15R-20R-49R-30
Zone 6MN, MT, ME, VT, WIR-15R-20R-49R-30
Zone 7AK Interior, NDR-15R-21R-49R-38
Zone 8AK Far NorthR-15R-21R-49R-38
Common Questions

Insulation & Code Questions Answered

What R-value does poured concrete have?
R-0.08 per inch. An 8″ basement wall = R-0.64 — far below code minimums. Always add insulation.
Closed-cell vs open-cell spray foam?
Closed-cell (R-6.5/in) is rigid and acts as a vapor barrier — ideal for basements and below-grade. Open-cell (R-3.7/in) is softer and more affordable but vapor-permeable.
XPS vs EPS vs Polyiso?
XPS (blue/pink, R-5/in) resists moisture — common below grade. EPS (white, R-3.8/in) is more economical. Polyiso (R-6/in) is the best above-grade performer but degrades in cold.
Do I need a vapor barrier?
Below grade: closed-cell spray foam or XPS acts as the barrier. Above-grade cold climates (Zones 5+): 6-mil poly on the interior (warm) side is typically required.
Does ICF meet code without extra insulation?
Yes — standard ICF at R-22 meets basement wall minimums in all 8 IECC zones (max required is R-15). ICF Plus at R-35 significantly exceeds code for cold climates.
What R-value for my basement?
Zones 1–2: none required. Zone 3: R-5. Zone 4: R-10. Zones 5–8: R-15. Select your zone above and the minimum updates automatically.