In May 2025 a retired farmer in Kaiapoi laid three quotes on his kitchen table and asked me which one was lying. His 1978 house had a long-run roof with rust through at the laps on the south side and a low-pitch lean-to over the laundry that had leaked since the February hail. The quotes were NZ$6,200, NZ$9,800 and NZ$14,400 for what he assumed was the same job. None was lying. They were describing three different jobs, and the cheapest had left out the two things that would decide whether his laundry ceiling was dry in 2030: the underlay and the fixings.
Start with what the quote does not mention
I read a roofing quote from the bottom up. The headline number tells you almost nothing. The exclusions and the words “as required” tell you where the cost will move once the old sheets come off. A quote that says “replace roofing to south elevation, 48 square metres, 0.40 mm Colorsteel, supply and fix” has not priced underlay, has not priced the purlins rotten under a rusted lap, and has not named the screw. The NZ$6,200 quote was that one. It was an honest price for the job it described. It was not the job the house needed.
Underlay: the line that gets dropped first
Roof underlay is required under E2/AS1 for almost every steel roof on a house. Its job is to catch condensation off the underside of the sheet and carry it to the spouting. On a 1978 roof the original bitumen paper is usually torn or missing. When a partial reroofing quote does not itemise new underlay, it is either going back over the old paper or skipping it entirely. Ask. Synthetic self-supporting underlay adds NZ$8 to NZ$14 per square metre laid, and it is not the place to save.
The lean-to raised a different question. Below about 3 degrees of pitch, long-run steel should not be used at all; a butyl or TPO membrane on plywood at NZ$180 to NZ$260 per square metre is the correct answer. The NZ$14,400 quote was the only one that had measured the pitch.
Fixings: the cheapest place to ruin a roof
A quote should name the screw. In the High wind zone that covers most of Kaiapoi and Rangiora under NZS 3604, that means a Class 4 coated hex-head screw with an EPDM sealing washer, fixed at every rib at the ridge, eave and laps, and at every second rib mid-sheet. Class 3 screws are cheaper by about a third and rust at the head within eight years here; I have inspected 2010 roofs with every screw head bleeding. The quote should also state whether it is fixing to timber or steel purlins, because the screw is different. If it says “fixings” with no description, the cheapest screw on the shelf is what will arrive. On a 48 square metre section that is roughly 450 screws, and the difference between Class 3 and Class 4 is about NZ$90. It is not where a NZ$3,600 gap between quotes comes from, which is exactly why it gets skipped.
The other lines I look for
- Purlin replacement. Priced as a rate with an allowance, for example “allow 12 lineal metres at NZ$35, adjusted on actual.” A quote with no allowance will send a variation invoice.
- Flashings. Barge, apron and ridge flashings listed separately, in material and colour matched to the sheet. Reusing thirty-year-old flashings on new steel is common and wrong.
- Edge protection and access. Scaffold or edge rails on anything over 3 metres are not optional under current WorkSafe guidance; if they are missing from the quote they are either being skipped or arriving later as an extra of NZ$1,200 to NZ$2,500.
- Disposal. Old steel is recyclable; old underlay and any asbestos-containing material under a 1970s roof is not, and testing for it should be named.
- Sheet grade, paint system and colour. Colour affects more than appearance; the heat a dark roof takes on changes how long the coating lasts, and there is a fuller discussion of how roof colour changes coating life elsewhere on this site.
- Warranty in writing. A product warranty from the steel supplier and a separate workmanship warranty from the installer, with conditions stated. Members of a trade body such as the Roofing Association of New Zealand generally provide a documented one.
What the Kaiapoi quotes turned out to be
Once the three were compared line by line, the NZ$9,800 quote was missing edge protection and the lean-to membrane and would have finished near NZ$13,000. The NZ$14,400 quote included everything, named its screws and its underlay, and carried a purlin allowance. The farmer took it, and the allowance came down after only 6 metres of purlin needed replacing. Final invoice NZ$13,900. The lesson he took away was that the cheapest quote is not a price. It is a list of things you have not been told about yet.
Frequently asked questions
Should a roofing quote include new underlay? Yes, for any section where sheets are removed. Synthetic underlay costs NZ$8 to NZ$14 per square metre laid and is required under E2/AS1 to manage condensation; if it is not itemised, ask why.
What screws should be specified on a Canterbury roof? Class 4 coated hex-head screws with EPDM washers, at every rib at the ridge, eave and laps. Class 3 screws rust at the head within about eight years inland and sooner on the coast.
Why do roofing quotes for the same house differ so much? Usually because they describe different scopes. Compare exclusions, purlin allowances, edge protection, flashings and membrane on low-pitch sections before comparing the totals.