NCC 2025 Volume Two 10.8.3 — Calculator
Calculates roof space ventilation requirements for buildings in Climate Zones 6, 7 & 8
1
What is the roof pitch?
See 2025 Calculation Reference Table ▾
| Roof Pitch | Condition | Eave / Low Level Open Area | High Level Open Area |
|---|---|---|---|
| Under 10° | Area <10 m², not skillion | 7,000 mm²/m (two opposing ends only) | Not required |
| Area <10 m², skillion | 7,000 mm²/m (two opposing ends only) | 5,000 mm²/m | |
| Area ≥10 m², not skillion | 20,000 mm²/m (two opposing ends only) | Not required | |
| Area ≥10 m², skillion | 20,000 mm²/m (two opposing ends only) | 5,000 mm²/m | |
| 10° – 75° (all types) | — | 7,000 mm²/m | 5,000 mm²/m |
Rates are minimum free open area (mm²) per linear metre of the longest horizontal roof dimension (Y).
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