Guides

Roofing estimating guides

How a New Zealand roof is actually measured, counted and priced — the arithmetic, the trade vocabulary, and the parts that cost people money when they get them wrong.

These guides cover the estimating side of long-run steel roofing in New Zealand: what each flashing is and where it goes, how sheet lengths and counts are worked out, what pitch changes and by how much, and how the steel grades differ once you are near the coast. They are written by a working roofing company, and every figure in them has been checked.

The guides

Each one is the long version of a question that gets asked on site, written out properly rather than answered in a text message.

Case study: a re-roof quoted in ten minutesOne of our own jobs, before and after, with the founder's numbers and caveats. How to quote a re-roofThe whole method end to end — measure, count, price, and write the scope that protects you. Roof flashings explainedRidge, hip, valley, barge, apron and change-of-pitch: what each one does and where it goes. Calculating sheet lengths and countsRun length, cover width, overhang and laps — the arithmetic behind a cut list. Roof pitch explainedDegrees, ratios, and every single length on the roof that pitch quietly changes. Colorsteel grades comparedMAXAM, ColorCote, ColorZen and Zincalume — and how far from the sea each one belongs. Coastal zones and warrantiesEstablishing the zone for a real address, and the details that void a warranty after it is written. Flashing wastage, done per pieceWhy a flat percentage over-allows on the easy roof and under-allows on the hard one. Pipe flashings and back-traysDektites, trays and the five-piece boxed set — the items that go missing off a docket. Writing a re-roof scope of workWhat to include, and the exclusions that are the half protecting you.

The calculators

Two working tools. Both explain their arithmetic on the page, so you can check the answer by hand rather than trusting a box.

Roof pitch calculatorDegrees to ratio, and the multipliers for rafters, hips and valleys. Roofing sheet calculatorFace size and pitch in, sheet length and count out.

Who writes these

RoofMap Limited, started by a working roofer in Northland. RoofMap is the estimating software we built for our own jobs; these guides are the knowledge behind it, in plain form. If a figure here is wrong, we would rather hear about it than have it sit on the internet — support@roofmap.co.nz.

Questions

About these guides.

Are these guides specific to New Zealand?

Yes. The profiles, the steel grades, the coastal corrosion zones, the warranty tiers and the vocabulary are all New Zealand. Metric throughout — millimetres and metres, square metres for area.

The arithmetic — pitch factors, cover widths, sheet counts — is the same anywhere. The material and the environment are not.

Do I need RoofMap to use them?

No. Everything in these guides can be done with a tape, a calculator and a pad, and for a century it was. The guides describe the method; the software just does it faster and does not forget the back-trays.

How often are they reviewed?

Each guide carries the date it was last reviewed at the bottom of the page. Where a figure comes from a manufacturer — warranty terms, coating specifications — check the current published document before you rely on it in a quote, because those change and this page will not change with them.

Try it on one of your own roofs.

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