NZ Minimum Roof Pitch (E2/AS1): Tiles vs Metal

The requirement

Roof pitch is how steep your roof is. Lay it too flat for the material you’re using and water sits, or blows back under the laps, instead of running off. New Zealand’s national Building Code fixes this through clause E2 External Moisture, and the numbers actually used on site come from its Acceptable Solution, E2/AS1.

E2/AS1 doesn’t give one minimum pitch for “roofing.” It gives a different minimum for each material, because each sheds water differently:

These figures only hold up to a scope limit on how far the roof runs. E2/AS1 states each material’s minimum for a specific maximum rafter length or run — profiled metal up to an 18 m run (§8.4.4.1), metal tile up to a 12 m rafter (§8.3.3.2), and masonry (concrete/clay) tile up to a 4.5 m rafter (Table 8.2.3.1). All these minimums climb once the rafter or run gets longer — a longer run of water needs more fall to clear it in the same amount of rain. Past those length limits, the deemed-to-comply figures in E2/AS1 no longer apply and the roof needs a specific design.

A manufacturer can certify a lower pitch. E2/AS1’s numbers are the deemed-to-comply floor for the Acceptable Solution path — they’re not a hard physical limit on what any roof can do. A roofing manufacturer can have a lower pitch for their specific product accepted as an Alternative Solution, engineered and signed off outside E2/AS1’s scope. Don’t borrow that lower number for a different product; it’s tied to the manufacturer’s own testing and detailing.

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?

1. 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.
2. Turn it into degrees. A 1 m rise over a 4 m run works out to about 14 degrees. (The roof-pitch calculator does this bit for you.)
3. Check it against your material’s minimum. Laying corrugated profiled metal? Its minimum is 8°, so 14° clears it comfortably. Laying a concrete Type III tile, though, whose minimum is 25°? At 14° that same roof is well under — too flat for that tile, even though it was fine for the corrugated sheet. The material you pick changes whether the same roof passes.

Always check your rafter length or run against the scope limit for your material (4.5 m for masonry tile, 12 m for metal tile, 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 comparing 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.