# §150.1(c)6: Prescriptive air sealing
What it requires
A newly constructed residence must measure no more than 5.0 air changes per hour at 50 pascals (ACH50) on a blower-door test. The test runs after drywall, before finish flooring, with all interior doors open and exterior doors sealed. An ECC Rater (CHEERS-registered field-verification credential) runs the test and reports the result on a CF3R Installation Certificate.
The 5.0 ACH50 threshold is the prescriptive maximum. Tighter values (typically 3.0 ACH50 or lower) appear on high-performance projects and on the performance path as a trade-off variable.
When it applies
- Newly constructed single-family homes and detached ADUs.
- Additions that add a separate conditioned zone (the addition zone gets its own blower-door test if isolated from the existing house).
- Performance-path projects always model an air-leakage value; the §150.1(c)6 prescriptive floor is the baseline.
How we use it
We model the prescriptive 5.0 ACH50 value on the §150.1(c) design option and on the Hybrid option. The High-Performance Envelope option intentionally keeps the same air-leakage assumption — the envelope trade lives in the R-values, not the air barrier (tightening air sealing further only saves cost on the performance path, and our three options all clear prescriptive without invoking it).
The blower-door test is one of the field-verification line items the designer-CF1R checklist surfaces before submission. We coordinate the test through our ECC Rater credential as part of project close-out.
Common gotchas
- Drywall punctures from contractor follow-on trades (electricians, low-voltage installers) that aren't air-sealed before the test — a failed test means re-sealing and a re-test fee.
- Recessed can lights on the top-floor ceiling that bypass the air barrier — every can is a leak path. IC-rated air-tight cans help; un-rated cans don't.
- Combustion appliances (gas furnace, gas water heater) inside the building envelope skew the test result because they share return-air paths with the conditioned space. The fix is usually to seal the appliance closet.