Subfloor ventilation under Part 6.2 of the NCC 2022 Housing Provisions is a Deemed-to-Satisfy Provision: openings of at least 2000, 4000 or 6000 mm² per metre of wall by climatic zone, halved where the ground is sealed with an impervious membrane. Ground clearance is 150 mm, or 400 mm where installed termite management systems need inspection, subject to a reduction on sloping sites. This note quotes Part 6.2 and its scope.
What sets subfloor ventilation requirements under the NCC?
Clause H2D5 of NCC 2022 Volume Two states: “Performance Requirement H2P3 is satisfied for subfloor ventilation if it is in accordance with Part 6.2 of the ABCB Housing Provisions.” Part 6.2 is therefore a Deemed-to-Satisfy route, and the figures below are Deemed-to-Satisfy figures. The other route is a Performance Solution, assessed by the relevant authority assessing the building work.
Both South Australian schedules were checked for this note. The Housing Provisions schedule lists variations to Parts 4.2, 9.2, 10.2 and 13.1, so Part 6.2 is not among them. The Volume Two schedule replaces H2P3 with SA H2P3, which requires that moisture from the ground be prevented from causing “undue dampness or deterioration of building elements” and “unhealthy or dangerous conditions, or loss of amenity for occupants”, and sets requirements for barriers against ground moisture. It also varies H2D4 on masonry. It does not vary H2D5.
The ABCB records that NCC 2025 was published on 1 May 2026, and lists South Australia as “BCA: 1 May 2027 / PCA: 1 May 2026”. Which edition applies to a particular application is for the relevant authority or building certifier to confirm.
How much subfloor ventilation does the NCC require?
Clause 6.2.1(1)(a) requires openings in external walls and internal subfloor walls in accordance with Table 6.2.1a. The table sets the minimum aggregate opening area in mm² per metre of wall.
With no membrane: Zone A 2000, Zone B 4000, Zone C 6000. With the ground sealed with an impervious membrane: Zone A 1000, Zone B 2000, Zone C 3000. For illustration, 10 m of wall at 4000 mm²/m is an aggregate of 40,000 mm² of opening.
The explanatory information gives the reason for the lower column: rates may be halved “because humidity levels in the space will not be affected by moisture from the soil.”
Which climatic zone applies to subfloor ventilation in Adelaide?
Part 6.2 does not state a zone for Adelaide in its text. Figure 6.2.1a is a national map of three zones “based on the prevailing relative humidity”. Its legend reads: Zone A, 9am relative humidity below 60%; Zone B, 9am above 60% and 3pm above 40%; Zone C, 9am above 70% and 3pm above 60%. Adelaide is marked on the map close to a zone boundary, and the map is drawn at a national scale.
The explanatory information adds: “If reliable weather data is available, these descriptions may be useful in determining which zone a particular location is in.” It says the zones “were determined by analysis of the average relative humidity at 9 am and 3 pm in January and July”, using the season with the highest relative humidity, generally July for southern Australia. The zone for an address is a question for the designer, and for the relevant authority assessing the building work.
These are not the same zones as the eight climate zones used for energy efficiency. The climatic zones in Part 6.2 are lettered and based on relative humidity.
How high must the subfloor clearance be?
Clause 6.2.1(1)(b) requires clearance between the ground surface and “the underside of the lowest horizontal member in the subfloor” in accordance with Table 6.2.1b. For Zones A, B and C alike, the table sets 150 mm where a termite inspection or management system is not required, and 400 mm where termite inspection is required.
The table notes limit the higher figure: “400 mm clearance required only where termite management systems are installed that need to be inspected”. On sloping sites, “the 400 mm clearance required by (1) may be reduced to 150 mm within 2 m of external walls in accordance with Figure 6.2.1b.”
Where do subfloor vents have to go?
Clause 6.2.1(2) adds that a subfloor space must be cleared of all building debris and vegetation, have the ground graded in accordance with 3.3.3, “contain no dead air spaces”, have openings evenly spaced as far as practicable, and have openings “placed not more than 600 mm in from corners.”
Clause 3.3.3 requires the ground beneath suspended floors to be graded so that “the area beneath the building is above the adjacent external finished ground level and surface water is prevented from ponding under the building”.
In double leaf masonry walls, clause 6.2.1(3) requires openings in both leaves, aligned “to allow an unobstructed flow of air”. Clause 6.2.1(4) requires openings in internal subfloor walls to have an unobstructed area equivalent to that required for the adjacent external openings.
What if the subfloor is damp or floods?
Where the ground or subfloor space is “excessively damp or subject to frequent flooding”, clause 6.2.1(5) adds to (1) to (4) one of three measures: the required ventilation is increased by 50%; or the ground within the subfloor space is sealed with an impervious membrane; or subfloor framing is of the durability class or preservative treated timbers it lists, or steel in accordance with the NASH Standard it cites. The explanatory information gives high water tables, poor drainage and areas frequently affected by flooding or water inundation as examples.
A note to Table 6.2.1a covers walls where openings cannot be provided: “additional measures must be provided to ensure that the overall level of ventilation of the subfloor space is maintained.” It says these “may include measures similar to those in 6.2.1(5)”.
Does Part 6.2 apply to an existing home?
The explanatory information to clause 6.1.1 states: “Part 6.2 applies to the subfloor space of all suspended floors of a building or deck, including but not limited to, timber and steel-framed subfloors and suspended concrete slabs.” That describes the types of floor. It does not address age.
The NCC’s introduction states that it “primarily applies to the design and construction of new buildings”, and that in some cases it may also apply to “new building work” in existing buildings. Clause A3G1(3) adds that the NCC “is subject to, and may be overridden by, State or Territory legislation.” Part 6.2 does not say that an existing house must be altered to meet it.
For a renovation or extension, which provisions apply to the proposed work is a question for the relevant authority or building certifier for that application. That includes work that would cover or change existing subfloor openings.
Common Questions
What are the subfloor ventilation requirements in NCC 2022?
The Deemed-to-Satisfy Provisions in Part 6.2 of the NCC 2022 Housing Provisions set minimum aggregate openings of 2000, 4000 or 6000 mm² per metre of wall in climatic Zones A, B and C, or 1000, 2000 or 3000 mm² with the ground sealed with an impervious membrane. They also set ground clearance and opening placement. A Performance Solution is the other route.
Does an impervious membrane halve subfloor ventilation?
Table 6.2.1a of the NCC 2022 Housing Provisions gives half the opening area in each climatic zone where the ground is sealed with an impervious membrane, and the explanatory information says the rates may be halved. The other Part 6.2 provisions, including ground clearance, continue to apply. These are Deemed-to-Satisfy figures.
What is the minimum subfloor clearance under the NCC?
Table 6.2.1b of the NCC 2022 Housing Provisions sets 150 mm where a termite inspection or management system is not required and 400 mm where termite inspection is required. Its notes limit the 400 mm to termite management systems that need to be inspected, and allow a reduction to 150 mm within 2 m of external walls on sloping sites in accordance with Figure 6.2.1b.
What climatic zone is Adelaide for subfloor ventilation?
The text of Part 6.2 of the NCC 2022 Housing Provisions does not state one. Figure 6.2.1a is a national map that marks Adelaide close to a zone boundary, and the explanatory information says the humidity descriptions may help where reliable weather data is available. The zone for an address is for the designer and the relevant authority assessing the building work.
Does South Australia vary NCC Part 6.2 on subfloor ventilation?
The South Australian schedule to the NCC 2022 Housing Provisions does not list Part 6.2. The schedule to Volume Two replaces H2P3 with SA H2P3 and varies H2D4, and does not vary H2D5, the clause that points to Part 6.2. This was read on 2 November 2026, and the applicable edition is for the relevant authority or building certifier to confirm.
Sources
- NCC 2022 ABCB Housing Provisions — Part 6.2 Subfloor ventilation (clause 6.2.1, Tables 6.2.1a and 6.2.1b, Figure 6.2.1a, explanatory information)Accessed 2026-11-02
- NCC 2022 ABCB Housing Provisions — Part 6.1 Scope and application of Section 6Accessed 2026-11-02
- NCC 2022 ABCB Housing Provisions — Part 3.3 Drainage (clause 3.3.3)Accessed 2026-11-02
- NCC 2022 ABCB Housing Provisions — Schedule 8 South Australia (index of variations)Accessed 2026-11-02
- NCC 2022 Volume Two — Part H2 Damp and weatherproofing (H2P3, H2D5)Accessed 2026-11-02
- NCC 2022 Volume Two — Schedule 8 South Australia, Part H2 (SA H2P3, SA H2D4)Accessed 2026-11-02
- NCC 2022 Volume Two — Schedule 8 South Australia (index of variations)Accessed 2026-11-02
- NCC 2022 Volume Two — Part A3 Application of the NCC in States and Territories (A3G1)Accessed 2026-11-02
- NCC 2022 Volume Two — Introduction to the National Construction CodeAccessed 2026-11-02
- ABCB — NCC 2025 state and territory adoption informationAccessed 2026-11-02
This page describes legislation as it stood on the access dates above. It is not legal advice about any particular property.
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