What blower door test result does the 2021 IECC require?

Under the 2021 IECC, a dwelling must test at or below 5 ACH50 in Climate Zones 0–2 and 3 ACH50 in Climate Zones 3–8 — air changes per hour at 50 pascals of test pressure, measured with a blower door.

Key details:

• Testing is to ANSI/RESNET/ICC 380, ASTM E779 or ASTM E1827
• Attached dwelling units have an alternative compliance path: an air leakage rate not exceeding 0.30 CFM50 per square foot of the dwelling unit enclosure area
• The test is performed by an approved third party — commonly a RESNET HERS rater, BPI analyst or jurisdiction-approved tester
• States frequently amend these limits when adopting the code (some apply a single statewide figure), so always confirm the requirement actually adopted for the project's location

ACH50 is calculated from the measured CFM50 and the conditioned volume: ACH50 = CFM50 × 60 ÷ volume. A failed test is normally followed by targeted air-sealing and a re-test.

CertBox includes a blower door air leakage test report that records the test standard, dwelling preparation, CFM50/ACH50 results and the adopted limit, with a professional PDF for the builder or code official.