Metal roof vs roof tiles on a new Adelaide house

How does the NCC deal with metal roofs and tiled roofs?

Clause 7.1.1(1) of the Housing Provisions states that Section 7 “sets out the Deemed-to-Satisfy Provisions for” metal sheet roofing (Part 7.2), roof tiles (Part 7.3), gutters and downpipes (Part 7.4) and timber and composite wall cladding (Part 7.5). Its explanatory information adds: “It should be noted that other construction methods may be used to achieve the same results as specified in this Part provided they comply with the appropriate Performance Requirements.”

Volume Two sets the Performance Requirements. Under H2P2, “A roof and external wall (including openings around windows and doors) must prevent the penetration of water” that could cause unhealthy or dangerous conditions or loss of amenity for occupants, or undue dampness or deterioration of building elements. Clause H2D1 provides two routes: under H2D1(1), a Deemed-to-Satisfy Solution satisfies H2P1 to H2P3 by complying with H2D2 to H2D8; under H2D1(3), where a Performance Solution is proposed, “the relevant Performance Requirements must be determined in accordance with A2G2(3) and A2G4(3) as applicable.”

For roofing, H1D7(2) lists the Deemed-to-Satisfy options for sheet roofing: AS 1562.1 for metal roofing, AS 1562.3 for plastic sheet roofing, or “Part 7.2 of the ABCB Housing Provisions, provided the building is located in an area with a wind class of not more than N3.” H1D7(3) does the same for roof cladding: AS 4597 for terracotta, fibre-cement and timber slates and shingles, and for roof tiles either AS 2050 or Part 7.3, provided the building is in an area with a wind class of not more than N3, “the roof tiles comply with AS 2049”, and “the roof has a pitch of not less than 15 degrees and not more than 35 degrees.” H2D6(4) then treats roof cladding complying with H1D7(2) or (3) as satisfying H2P2. This note does not describe the content of the Australian Standards named.

South Australia’s variations to Volume Two Part H1 list only SA H1P2 (buildings in flood areas), which that page shows as deliberately left blank, and the index of its Housing Provisions variations in Schedule 8 lists Parts 4.2, 9.2, 10.2 and 13.1 and the referenced documents. Section 7 is not among them.

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What roof pitch does each one need?

For metal sheet roofing, clause 7.2.3 states: “Metal sheet roofing must comply with the minimum pitch requirements for the associated roof profile in accordance with Figure 7.2.3.” The minimum depends on the profile, and the figure is not reproduced here. A note to the figure adds that “consideration should be given to the drainage run off capacity of the roof sheeting when determining the minimum pitch and total length of the roof sheet.”

Clause 7.2.6 asks for sheets to be laid “wherever possible using complete lengths from the fascia to ridge”. Where that is not possible, each run is laid from bottom to top, with a minimum end lap “for roof slopes above 15 degrees (1:4) – 150 mm” and “for roof slopes between 5–15 degrees (1:12-1:4) – 200 mm”.

For roof tiles, the Part 7.3 route itself is limited by H1D7(3) to a pitch “of not less than 15 degrees and not more than 35 degrees.” Within that range, the pitch also decides whether sarking and an anti-ponding board are needed, as the next section sets out. H1D7(3) lists AS 2050 as the other Deemed-to-Satisfy route for roof tiles.

Does a tiled roof need sarking, and what about a metal roof?

Clause 7.3.4 requires sarking under roof tiles “in accordance with Table 7.3.4”. The table sets a maximum rafter or truss top chord length without sarking, measured from the apex down: 4 500 mm for a pitch of 18° or more and less than 20°, 5 500 mm for 20° or more and less than 22°, and 6 000 mm for 22° or more. Where that length is exceeded, its notes require sarking over the remainder towards the eave line, and add: “All tiled roofs with a pitch less than 18 degrees must be provided with sarking, regardless of rafter/truss chord length.”

The same clause requires the sarking to comply with AS 4200.1, with adjoining sheets or rolls “overlapped not less than 150 mm” or taped together, fixed to supporting members “at not more than 300 mm centres”, and with “no sags more than 40 mm”. Clause 7.3.5(1) adds an anti-ponding device or board where sarking is installed on “roofs with a pitch less than 20°” and on “roofs with no eaves overhang, regardless of the roof pitch.”

Part 7.2 does not set a sarking rule for metal sheet roofing. Part 10.8 addresses roof-space condensation, and Section 13 addresses energy efficiency; the applicable provisions and the specified roof build-up need to be checked for the design. The note on condensation management covers Part 10.8.

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Metal roofing near the coast: corrosion and mixed metals

Clause 7.2.2(1) requires metal sheet roofing to be “protected from corrosion in accordance with Table 7.2.2a”, which sets a minimum metal coating, by reference to AS 1397, for four environment categories from Low to Very High. The table describes the locations, for example Medium as “typically more than 1 km from breaking surf or aggressive industrial areas or more than 50 m from sheltered bays”, and lists some coatings as “Not suitable” in the most severe category.

The notes to the table mention South Australia twice. Under Low: “some suburbs of cities on sheltered bays such as Melbourne, Hobart, Brisbane and Adelaide that are more than 1 km from the sea. However each of these have many exceptions which are in more corrosive categories.” Under Medium: “This can extend to 30 to 70 km inland in South Australia”. They also state: “All locations described in the table contain variations of greater corrosion severity. If significant, this must be addressed by designing for the most severe environment.”

Clause 7.2.2(2) requires different metals in a roofing system, “including flashings, fasteners, guttering, downpipes, etc.”, to be compatible with each other as described in Tables 7.2.2b to 7.2.2e, and adds three limits: “no lead materials can be used upstream from aluminium/zinc coated materials”, “no lead materials can be used on roofs that form part of a drinking water catchment area”, and “no copper materials can be used upstream from galvanized coated materials.”

Clause 7.2.7(1) repeats the point for flashings: “Lead flashings must not be used with prepainted steel or zinc/aluminium steel or on any roof if the roof is part of a drinking water catchment area.” Part 7.3 has its own version of the drinking-water limit. Clause 7.3.3(6) states: “Lead flashings must not be used on any roof that is part of a drinking water catchment area.” Clips used to fix tiles under 7.3.2(2) must be non-ferrous metal, stainless steel or steel protected from corrosion in accordance with Tables 7.2.2b, 7.2.2c and 7.2.2d.

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How are sheets and tiles fixed and flashed?

Clause 7.2.5 requires metal sheet roofing to be crest fastened or to have concealed fasteners, fixed at the spacings in Table 7.2.5, using fixings of a compatible metal, and, where clipped and pierced fastening are both used, with an anti-capillary feature in the side lap. Table 7.2.5 sets the fixing pattern by profile: for corrugated and close pitched trapezoidal sheet, “side lap and every second rib” in end spans and “side lap and every third rib” in internal spans; for trapezoidal and concealed-fastener profiles, every rib. The notes to Table 7.2.4 limit the sheet run for pierced fixed profiles to “not greater than 25 m when measured between the fasteners at the ends of the sheet.”

For tiles, clause 7.3.2 and Table 7.3.2 set the fixing by wind class. In N1 and N2, the table requires every full tile in the second course in from the edge of the roof to be fixed, and in the field of the roof “every second tile in every course, or every tile in each alternative course.” In N3, it requires each full tile in every second course from the second course in at the edge, and “every second full tile in every course” in the field. Ridge, hip, barge and valley tiles are fixed “each tile” in all three classes. The explanatory information defines the edge of roof as “a 1.2 m wide band bounded by the eaves, hips and barge”.

Clause 7.2.7(1) requires joints in metal flashings and cappings to be “not less than 75 mm, lapped in the direction of the fall of the roof”. For tiles, clause 7.3.3(2) requires wall and step flashings to allow “not less than 75 mm upturn to the wall and a minimum of 150 mm in width and moulded into the tiles”, and 7.3.3(3) requires penetration flashings to “permit the total drainage of the area above the penetration.”

Where an eaves gutter is provided, clause 7.2.8 requires metal sheets to overhang the fascia (or end batten) “by not less than 50 mm”, and clause 7.3.6 requires tiles to overhang the fascia or tiling batten “by not less than 35 mm”.

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Bushfire-prone land, roof spaces and attached houses

Three other topics sit outside Parts 7.2 and 7.3 and are not repeated here. Construction on bushfire-prone land is covered in the note on BAL ratings. Roof-space ventilation and condensation are in Part 10.8, covered in the note on condensation management.

For attached houses, the explanatory information to clauses 7.2.1 and 7.3.1 points to Part 9.3 of the Housing Provisions “for sheet roofing over a separating wall”, the wall common to adjoining Class 1 buildings. Part 9.3 is not covered in this note.

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Which roof decisions do the drawings settle?

Each limit above depends on facts about the site and the design. The wind class decides whether Parts 7.2 and 7.3 can be used at all and, for tiles, how they are fixed; the explanatory information to both Parts says information on design wind speeds for particular areas “may be available from the appropriate authority.” The corrosion environment decides the coating under Table 7.2.2a. The profile decides the minimum pitch; the slope decides the end laps (7.2.6). For tiles, the pitch decides the sarking and anti-ponding requirements (7.3.4, 7.3.5).

Those choices — profile, coating, pitch, sarking, flashing and fixing — are recorded in the drawings and specification for the house. NCC 2025 was published on 1 May 2026, and the ABCB’s adoption page lists South Australia as “BCA: 1 May 2027” and “PCA: 1 May 2026”. Which edition applies to a particular application is for the relevant authority assessing it to confirm.

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