| Primary value | 0.37 m² |
| Applies to | Bathrooms with external wall · WCs with external wall |
| Exceptions | Internal bathrooms (no ext wall) → Mechanical exhaust required |
| Measured as | Openable window area connecting to outside air (not internal courtyard <3m wide). |
| Source | NBC 2016 — Part 4, Clause 4.3 ✓ Verified |
Bathrooms generate steam, odours, and humidity that damage finishes and breed mould. 0.37 m² is the smallest opening that lets natural ventilation clear these in normal use.
Most bathrooms provide 0.5-0.7 m² of high-level window (above eye level for privacy) plus a powered exhaust fan for fast removal.