The requirement
Roof pitch is how steep your roof is. Lay it too flat and water sits on it instead of running off. So there’s a minimum — the flattest you’re allowed to go. The catch is that the minimum is set in two different ways depending on what you’re laying (NCC 2025, Housing Provisions Parts 7.2 and 7.3).
| What you’re laying | Who sets the minimum pitch |
|---|---|
| Metal sheet roofing | The NCC — your profile’s minimum is in Figure 7.2.3 |
| Roof tiles | Your tile maker — check AS 2050 / the manufacturer |
Metal sheet roofing — the code fixes it. For metal sheet, the NCC itself sets the smallest pitch you can lay each profile at (clause 7.2.3, via Figure 7.2.3). It does not pass this off to AS 1562. Each profile has its own minimum:
| Metal sheet profile | NCC minimum pitch |
|---|---|
| Corrugated | 5° |
| Trapezoidal (incl. close-pitched) | 2° |
| Concealed-fastened (secret-fix) | 1° |
Those are the code minimums straight off Figure 7.2.3. Your sheet maker often asks for more than the code for their particular product, so check the product sheet too — and never lay flatter than whichever number is higher. The calculator turns your rise over run into degrees, so you get a number you can hold up against your profile’s minimum.
Roof tiles — the tile maker fixes it. For tiles it works the other way. The NCC does not set a minimum tile pitch. That number comes from your tile manufacturer and AS 2050 — the tiling standard. AS 2050 covers roofs at 15 degrees or more; go flatter than that and you ask the tile maker directly. So don’t lift a tile minimum off another job — check the fixing sheet for the tile you’re actually laying.
One more tile rule — sarking. A tiled roof pitched under 18 degrees must be given sarking — the foil-backed blanket that runs under the tiles and catches wind-driven rain and dust. Watch this one: 18 degrees is a sarking trigger, not a minimum pitch. It tells you when the sarking goes in, not how flat you’re allowed to lay the tiles.
Worked example
You’ve framed a roof. The rafters climb 1 m over a 4 m run. What’s the pitch, and is it steep enough?
- Get the rise and the run. Rise is how far the roof climbs — 1 m. Run is how far it travels flat to get there — 4 m.
- Turn it into degrees. A 1 m rise over a 4 m run works out to about 14 degrees. (The calculator does this bit for you.)
- Check it against the minimum. Now hold that 14 degrees against your profile’s minimum. Running corrugated? Its minimum is 5 degrees, so 14 is well clear — you’re right. Even a near-flat concealed-fastened profile (1 degree) passes. If your roof had come out below the profile’s minimum, you’d be too flat and would need to lift the pitch or change profile — and always check your sheet maker’s spec, since it can ask for more than the code.
Laying tiles instead? Work out the same 14 degrees, but check it against your tile maker’s minimum and AS 2050, not Figure 7.2.3 — and remember anything under 18 degrees needs sarking.
Do it in 5 seconds
Related
- Part of the NCC rule book for Australian chippies — the pillar, with the plain-English tour of what actually applies to your work.
- Getting water off the roof once it runs down: gutters & downpipes: NCC sizing basics.
Sources
- NCC 2025, ABCB Housing Provisions Standard, Part 7.2 “Sheet roofing” (clause 7.2.3, Figure 7.2.3) — sets the minimum pitch for each metal sheet profile: corrugated 5°, trapezoidal 2°, concealed-fastened 1° (confirmed against NCC 2025 Figure 7.2.3, and unchanged from NCC 2022). Manufacturers may specify higher. See ncc.abcb.gov.au.
- NCC 2025, ABCB Housing Provisions Standard, Part 7.3 “Roof tiles and shingles” — the under-18-degree sarking trigger for tiled roofs. Confirm at ncc.abcb.gov.au.
- AS 2050 (Installation of roof tiles) and your tile manufacturer — set the minimum installable tile pitch; the NCC does not. AS 2050 applies to roofs at 15 degrees or more; below that, check with the tile manufacturer. The tile pitch figure must be confirmed there, not from the NCC.