Air Leakage Between Attached Units
Reduce air movement between attached housing units. Stringency tightens at higher tiers (ACH50 thresholds differ for new construction vs. renovation).
Spec by tier
This requirement steps in stringency by tier. Each tier inherits and tightens the value.
Scope
Air leakage between adjoining dwelling units in attached housing — duplex, townhouse, multifamily, ADU sharing a wall. Single-family detached homes are exempt.
Requirements
Performance targets
- 01.
Perform a blower-door test specifically isolating air leakage between the test unit and adjoining units (pressurize the test unit and measure airflow into the neighbor units).
- 02.
Measured air leakage between units must meet the tier threshold in the "Spec by tier" table above. Each tier has separate values for new construction and existing/renovation.
Documentation
Evidence the inspector / Institute will need.
- 01.
Blower-door test report from a RESNET-certified or BPI-certified rater, showing inter-unit air leakage measurements in CFM50 or ACH50.
- 02.
Floor plan marked with leak-test locations.
Guidance
Why it matters more in attached housing
In a single-family detached home, air leakage means heat loss + comfort issues — annoying, not unsafe. In attached housing, inter-unit air leakage moves combustion gases, cooking odors, allergens, secondhand smoke, and noise between dwelling units. A unit can fail its CO test because of a neighbor's furnace.
Common leak locations
Shared chases for plumbing and HVAC, electrical penetrations through the demising wall, unsealed top plates above the demising wall (especially under a common attic), and gaps where the demising wall meets exterior walls. Aerosolized sealant ("AeroBarrier") is increasingly used in multifamily new construction for hard-to-reach demising-wall seams.
Resources
- ASTM E779 — Air Leakage Measurement
The blower-door test method most jurisdictions reference.
- AeroBarrier →
Aerosolized envelope sealant used to hit aggressive ACH50 targets without manual caulking.