Topic

Airtightness

A Passive House has one continuous airtight layer around its heated space. It should be drawn on every section, traceable around the building without lifting the pencil, including at every transition, penetration, and window, where leaks happen.

Leaks carry moisture. Warm indoor air holds water vapor; when it leaks out through a wall or roof in winter, it meets colder layers and leaves its water there. Air can carry far more moisture than diffusion through materials: over a cold-climate heating season, a 4×8 sheet of drywall passes about a third of a quart of water by diffusion, and about 30 quarts through a 1-inch square hole. In cold weather, most condensation damage inside walls and roofs starts at an air leak.

Leaks also bring drafts and cold floors, let outdoor pollution in, and let heated or cooled air out. In an airtight building, fresh air comes in through ventilation with heat recovery.

A blower door test measures airtightness: the building is pressurized to 50 pascals, then depressurized to −50, and the airflow needed to hold each is measured. For Passive House, the average may not exceed 0.6 air changes per hour (n50). For EnerPHit and PHI Low Energy Building, the limit is 1.0. The test should be run during construction, while the airtight layer can still be reached and repaired.

Training on this topic

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I am A designer or consultant 9 A builder or tradesperson 7 An owner or developer 4 A policymaker or advocate 1

Kind Certification courses 0 Specialized courses 3 Paid sessions 4 Free sessions 3

Building type Single-family 2 Multifamily 0 Non-residential 0

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Credit AIA LU 7 PHI credit 6 Counts toward CPHD/C renewal 7 Counts toward CPHT renewal 7

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10 courses and sessions

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