About this calculator
Work out the roof space ventilation the NCC 2022 condensation provisions ask for in climate zones 6, 7 and 8, and count vent strips.
How it’s calculated
Under NCC 2022 Housing Provisions 10.8.3: below 10°, provide 25,000 mm² per metre at each of two opposing ends. From 10° to under 15°, 25,000 mm²/m at the eaves plus 5,000 mm²/m at high level. From 15°, 7,000 mm²/m at the eaves (25,000 with a cathedral ceiling) plus 5,000 mm²/m at high level.
Worked example
With these inputs:
- Total eaves length (both sides)
- 20 m
- Ridge length
- 10 m
- Roof pitch (degrees)
- 22.5
- Cathedral (raked) ceiling
- No
the result is:
- Eaves (low-level) openings
- 7,000 mm² per metre
- High-level openings
- 5,000 mm² per metre = 50,000 mm²
Tips from the trade
- Baffles or rafter trays keep insulation from blocking the eaves.
- Don’t mix ridge vents with gable or powered vents on the same attic. They short-circuit each other.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the NCC and Australian Standards before ordering.