Air-tightness target: ≤ 3.0 ACH50 (IECC 2021 base); ≤ 1.5 ACH50 for Passive House / ZERH
IECC R-value (DOE climate-zone) — Air Leakage — blower door targetDescription
IECC 2021 + 2024 set the residential air-leakage maximum at 3.0 ACH50 (air changes per hour at 50 Pascals pressure differential) for Climate Zones 3 and above. Verified by a blower-door test by a 3rd-party rater. Higher-performance targets: ENERGY STAR typically targets the same or stricter (sometimes 2.0 ACH50); Passive House requires 0.6 ACH50; DOE ZERH typically targets 1.5 ACH50.
Why this exists
3.0 ACH50 is dramatically tighter than typical 1980s construction (often 8-15 ACH50). It demands deliberate air-sealing — air-barrier continuity must be drawn AND inspected. The blower-door test is the only way to know; visual inspection isn't reliable.
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
iecc2021 | max | 3 | ACH50 | IECC 2021 maximum (CZ 3+) |
energyStar | max | 2.5 | ACH50 | Typical ENERGY STAR climate-zone target |
passiveHouse | max | 0.6 | ACH50 | Passive House target |
Categories
Source
Solver enforcement
Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.
Related directives
- Natural light in habitable rooms · IRC R303.1
- Habitable space minimum ceiling height · IRC R305.1
- Carbon monoxide alarms in sleeping areas · IRC R315
- Wind design · IRC R301.2.1
- Seismic provisions · IRC R301.2.2
Last reviewed 2026-05-15.