Bathroom Exhaust Ventilation
Bath fans exhaust to the outdoors (verified with a toilet-paper test). Silver and above must also test to ≥ 50 CFM per bathroom.
Spec
Applies uniformly from Certified upward.
Scope
Exhaust fans in every bathroom — full bath, half-bath, and powder rooms with a permanent water source.
Requirements
- 01.
Every bathroom must have an exhaust fan that vents to the outdoors. Termination must be an exterior wall, soffit (where vented), or roof — NOT into the attic, eave, or wall cavity.
- 02.
At Certified: verify with a "toilet paper test" — hold a single ply of TP against the running fan and confirm it sticks.
- 03.
At Silver and above: flow-test the fan to confirm at least 50 CFM (per ASHRAE 62.2 minimum).
Documentation
Evidence the inspector / Institute will need.
- 01.
Photo of each bath fan termination (exterior wall hood, roof jack, or vented soffit).
- 02.
For Silver+: flow-test record (date, fan model, measured CFM at the grille).
Guidance
Why termination matters
A surprisingly large fraction of installed bath fans terminate inside the attic — the installer ran the duct but never finished it through the roof. Result: humid air dumps directly into the attic, condenses on the underside of the roof deck, and causes mold, ice damming, or even structural rot. The toilet-paper test verifies the fan moves air; visual inspection of the termination verifies that air goes outside.
Note
Common failure: rigid metal duct connected to a flex bath-fan inlet, with the connection unsealed by tape. Air leaks out at the joint and into the attic. Mastic the joint with HVAC tape (UL-181 rated) and you fix it permanently.
Resources
- ASHRAE 62.2 — Ventilation for Acceptable Indoor Air Quality in Residential Buildings
The bath-fan CFM minimum (50 CFM intermittent or 20 CFM continuous) comes from this standard.