New Zealand · metal roofing
Longrun roofing calculator
How many Colorsteel sheets, at what length, for a New Zealand roof you have already measured.
Longrun is sold by the lineal metre of sheet, cut to length, in a named profile. A useful calculator has to know the effective cover after the side lap — 760 or 762 mm on common corrugate, not the 851 mm overall blank. This page uses manufacturer cover widths from Dimond, Metalcraft and Stratco, and lets you override them when the coil in the yard is different.
Sheet length is the slope length: horizontal run from ridge (or high wall) to the eave drip, including overhang, divided by cos(pitch). We round the order length up to the next 50 mm so you can read it the same way a merchant will cut it. If that length exceeds the CoP “check capacity after …” figure for the profile height, you get a drainage warning rather than a silent pass.
Flashings are listed as lineal metres: ridge, barge, hip, valley, apron. Cover dimensions follow CoP 8.4 Category A or B from wind zone and pitch — Extra High is Category B at every pitch, which means a 200 mm ridge cover, not the 130 mm residential default.
FAQ
Is longrun the same as Colorsteel?
Colorsteel is a coating system from NZ Steel. Longrun is the way the sheet is rolled and cut to length. You can have longrun in Colorsteel, Zincalume or other finishes.
Do I order extra sheets for waste?
On a clean gable the sheet count is already rounded up per plane, so extra whole sheets are usually for damage and colour-batch insurance. Hip and valley jobs need a cutting allowance — the waste percentage on this page.