The National Construction Code (NCC) 2022 specifies that all subfloors shall be fitted with wall ventilation to allow air flow in the subfloor spacing area. The code recommends that the subfloor punched vent be installed in accordance to the climatic zone shown in Figure 6.2.1a from ABCB Housing Provisions of the NCC 2022 below. More humid areas require more ventilation as do walls with no membranes. Note that the recently released 2025 version has no changes from the 2022 regulations.
| Climatic zone (see Figure 6.2.1a) | Minimum aggregate subfloor ventilation openings with no membrane (mm2/m of wall) | Minimum aggregate subfloor ventilation openings with ground sealed with impervious membrane (mm2/m of wall) |
| A | 2000 | 1000 |
| B | 4000 | 2000 |
| C | 6000 | 3000 |
(Table 6.2.1a)
The minimum required sub-floor ventilation per linear metre of wall is recommended in Table 6.2.1a (shown above) in the ABCB Housing Provisions of the NCC 2022 to allow sufficient air flow within the subfloor space.
Alpine Ventilation has a range of 12 sub floor vents of different sizes – for both brick and cladding type walls. Some models have mesh for BAL-40 bushfire ratings. Some models are in z275 galvanised steel and others constructed from stainless steel.
Using the Alpine Ventilation Slimline Brick Vent 230 x 75mm (B2375) as an example on an 12m length wall on the ground with impervious membrane in Zone C of the climatic zone chart, the number of vents required as per NCC 2022 can be calculated as follows;
- Airflow of specific vent: 14,000mm2.
- Calculate the total ventilation area required on the wall reflecting NCC 2022 minimum requirements based on desired wall length = 12m x 3000mm2/m = 36000mm2.
- Number of vents required (12m length wall) = Total ventilation area (mm2)/Air flow area of one vent (mm2) = 36000mm2/14000mm2 = 2.57 ≈ 3 vents (rounded up).
INSTALLATION TIPS
Vents shall then be installed in even spacing along the length of the wall and not more than 600mm in from the corner. If building in areas which are prone to bushfire attack up to and including BAL-40, 2mm (or less) aperture steel or aluminium mesh is required to be installed in the vent to prevent entry of ember or wind carried burning debris into the house through the subfloor vent. Note that vents with metal mesh for BAL requirement have a smaller open area than an equivalent vent without mesh.
NOTE:
The above guide serves as a design guide based on the National Construction Code 2022. Consult a qualified engineer or architect to ensure sufficient ventilation is provided for subfloor spacing, adhering to applicable local building codes and Australian Standards.