All ventilation equipment must exhaust to the exterior of the building envelope
NKBA 4th ed §8.1 Ventilation PlanningDescription
All ventilation equipment — range hoods, bath fans, dryer vents — should be provided in every space and exhausted to the EXTERIOR of the building envelope. Recirculating range hoods are not a substitute. Make-up air may be required where the exhaust capacity exceeds the natural infiltration rate (typical threshold: 400 cfm exhaust).
Why this exists
Recirculating fans don't remove moisture, CO2, or combustion byproducts — they just filter particulate. Exhausting to the exterior is the only way to remove humidity (the #1 driver of mold) and combustion gases. Make-up air prevents backdrafting of natural-draft appliances (water heaters, fireplaces).
Measurements
| Property | Operator | Value | Unit | Note |
|---|---|---|---|---|
makeupAirThreshold | min | 400 | cfm | Exhaust capacity at which make-up air is typically required |
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
- Bathroom entry doorway · NKBA Bath 1
- Kitchen walkway and work-aisle widths · NKBA Kitchen 6
- Doorway clear width · NKBA Kitchen 1
- Door swing into work zones · NKBA Kitchen 2
- Distance between work zones · NKBA Kitchen 3
Last reviewed 2026-05-14.