💡 Designer tip: minimum pitch is the cladding pitch, not always the design pitch. Widely spaced purlins or long rafter runs can deflect enough that the built roof needs to be steeper than the cladding minimum – check the span tables. And the lower the pitch, the more the laps, underlay and flashings matter for keeping water out.

Please note: the minimum pitches here are the published NZ figures for common long-run metal roofing (corrugate 8°, trapezoidal 3-4°, trough 3°, long-run metal tile 8°, pressed metal tile 15°). Tile and membrane minimums depend on underlay and the specific product, so those are covered by E2/AS1 and the manufacturer’s specification, not a single figure. Always confirm the exact minimum for your product with the NZ Metal Roofing Code of Practice and E2/AS1.

How do I convert roof pitch from degrees to a ratio?

The ratio is the rise over a given run. Take the tangent of the angle and multiply by 12 for the “x in 12” form, or divide 1 by the tangent for the “1 in x” form. An 18.4° pitch works out to 4 in 12, or 1 in 3 – this tool gives you both.

What is the minimum pitch for a metal roof in NZ?

Under the NZ Metal Roofing Code of Practice, corrugate is 8°, trough profiles 3°, and trapezoidal 3-4° depending on the rib height. Long-run metal tiles are 8° and pressed metal tiles 15°. These are cladding minimums – your specific profile and the manufacturer can require more.

Is the minimum pitch the same as the design pitch?

Not always. The minimum is the roof cladding pitch. A roof with widely spaced purlins or portals can deflect enough that the finished roof needs a steeper design pitch to stay above the minimum, so check the span tables for your framing.

Designing a roof and want it detailed right? We work the pitch, cladding and weathertightness together from the first sketch.

Talk to our design team