The requirement
New Zealand has no single minimum roof pitch. E2/AS1 sets a minimum for each kind of roofing. It runs from 3° for trough profiled metal up to 25° for some concrete and clay tiles. Each minimum also climbs once the rafter or run gets longer.
Roof pitch is how steep your roof is. Lay it too flat for the roofing and water sits. Or it blows back under the laps instead of running off. The rule sits in clause E2 External Moisture of the national Building Code. The numbers used on site come from its Acceptable Solution, E2/AS1.
Each kind of roofing sheds water in its own way. So E2/AS1 gives each one its own minimum pitch:
| Roofing material | Minimum pitch (E2/AS1) |
|---|---|
| Profiled metal — trough | ≥ 3° |
| Profiled metal — trapezoidal | ≥ 3–4° (crest-height dependent) |
| Profiled metal — corrugated | ≥ 8° |
| Metal tile — standard profile | 12° |
| Metal tile — shingle/shake-look profile | 15° |
| Concrete tile Type I | 15° with underlay · 20° without |
| Concrete tile Type II | 20° |
| Concrete tile Type III | 25° |
| Clay tile | 20–25° (profile/underlay dependent) |
These figures only hold up to a length limit. Profiled metal is covered up to an 18 m run (§8.4.4.1). Metal tile is covered up to a 12 m rafter (§8.3.3.2). Masonry tile, concrete and clay, is covered up to a 4.5 m rafter (Table 8.2.3.1). A longer run of water needs more fall to clear it in the same rain. So each minimum climbs as the rafter or run gets longer. Past those length limits the E2/AS1 figures no longer apply. The roof then needs a specific design.
A maker can go lower. The E2/AS1 numbers are the floor for the Acceptable Solution path. They are not a hard limit on what any roof can do. A maker can have a lower pitch for their own product signed off as an Alternative Solution. That route sits outside E2/AS1. Never borrow that lower number for another product. It is tied to the maker’s own testing and detailing.
Worked example
You have framed a roof. The rafters climb 1 m over a 4 m run. What is the pitch, and is it steep enough?
- Get the rise and the run. The rise is how far the roof climbs: 1 m. The 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 is about 14 degrees. The roof-pitch calculator does this bit for you.
- Check it against your roofing’s minimum. Laying corrugated metal? Its minimum is 8°, so 14° is well clear. Laying a concrete Type III tile? Its minimum is 25°, so the same 14° roof is too flat. The roofing you pick changes whether the roof passes.
Always check your rafter length or run against the scope limit. That is 4.5 m for masonry tile, 12 m for metal tile, and 18 m for profiled metal. A longer roof needs more pitch than the table above shows.
Related
- New Zealand Building Code hub — how the one national Code and its Acceptable Solutions work.
- NCC minimum roof pitch (Australia) — the Australian numbers, for anyone working across the ditch.
Sources
- NZ Building Code Clause E2 External Moisture — Acceptable Solution E2/AS1 (4th edition, effective 28 July 2025), §8.2.3 and Table 8.2.3.1 (masonry tiles, rafter ≤ 4.5 m), §8.3.3.2 (metal tile roofing, rafter ≤ 12 m), and §8.4.4.1 (profiled metal roofing, run ≤ 18 m) — the source for every figure on this page. Confirmed by direct read of the current PDF at building.govt.nz. E2/AS1 itself notes a manufacturer may have a lower pitch accepted outside its scope — its figures are a deemed-to-comply floor, not an absolute physical limit.
Read this first. These are the Acceptable Solution (E2/AS1) figures — the deemed-to-comply path. A designer can instead use a Verification Method or an Alternative Solution, which can carry different numbers for a specific product. Always confirm the current amendment at building.govt.nz before you build to it.
Related building rules
More New Zealand rules