When do you need a longrun roofer?
For a new roof or a re-roof, and for smaller jobs too: rusted sheets, failed screws, tired flashings around chimneys and skylights, or leaks at laps and valleys. Sheets are made to length, so swapping a damaged one usually means a new full-length sheet from ridge to spouting.
If you're chasing a specific problem, our guides to a rusty iron roof and popping nails and failing screws are a good first stop.
Corrugate, rib or tray?
| Corrugate | Trapezoidal rib | Tray or standing seam | |
|---|---|---|---|
| Look | Rounded waves, the classic Kiwi roof | Sharper raised ribs | Flat pans and clean modern lines |
| Minimum pitch, as RANZ gives it | 8 degrees for standard corrugate | 3 degrees | 3 degrees |
| Fixing | Screws through the sheet | Screws through the sheet | Often hidden clips, with no screws through the roof |
| Worth knowing | Deeper corrugates can go lower than standard | Generally, the higher the rib, the stronger the sheet | Some systems need a plywood base, others span purlins |
Which steel suits your site?
Unpainted ZINCALUME has a silvery matt finish that darkens over time, and NZ Steel says it lasts significantly longer than galvanised steel. NZ Steel doesn't recommend ZINCALUME in its Severe, Very Severe or Extremely Severe categories, which are the ones closest to the coast.
Pre-painted COLORSTEEL comes as two products. MAXAM covers most of the country, inland and coastal, but isn't recommended in the Extremely Severe category right by breaking surf. ALTIMATE, a marine-grade aluminium, is warranted there. Some rollformers also offer ColorCote, another pre-painted steel.
Two systems describe exposure, and they don't line up. The Building Code's E2/AS1 uses NZS 3604 exposure zones B to E, while NZ Steel's warranties use its own categories, Mild to Extremely Severe, measured differently. Ask your roofer to confirm both for your address rather than guessing from a map.
Geothermal areas are a case of their own. The metal roofing Code of Practice treats highly active areas such as much of Rotorua as geothermal even without a fumarole nearby, and NZ Steel asks anyone building there to check product advice with it first.
What good installation looks like
Most of what makes longrun last happens on installation day, and you can ask about all of it.
Sheets should be one length where they can. Dimond says end laps should be avoided, and where one can't be, it needs a sealed overlap of at least 150 mm. Roof underlay goes under all profiled metal longrun, which E2/AS1 requires.
Cutting matters. NZMRM, the metal roofing makers' body, says sheets should be cut with shears, not friction or high-speed blades, and Dimond says any disc cutting voids the material warranty. Swarf, the filings from cutting, should be cleared off the roof daily.
Fixings should suit the site: Dimond calls for exposed fasteners of at least Class 4, and Class 5 in what it calls Very Severe environments. At the spouting, NZMRM and Dimond give a minimum sheet overhang of 50 mm for pitches between 10 and 35 degrees, so wind doesn't blow water back under.
Looking after a longrun roof
Rain does most of the work. For COLORSTEEL roofing, rain washing is the only routine care NZ Steel asks of the open roof, in every category. Sheltered spots are different: soffits, under spouting, beneath solar panels and anywhere rain can't reach need hand washing, as often as monthly in the harshest sites, and it's a warranty condition.
Leave scratches alone. NZ Steel doesn't recommend touch-up paint on COLORSTEEL, because the metal coating underneath still protects the steel. Keep copper pipes and lead flashings from draining onto the roof, since that speeds up corrosion.
When the paint finally tires, a repaint can extend the roof's life, though the COLORSTEEL warranty doesn't cover a paint system added later. Our roof painting page covers that.
What a longrun quote should name
- The brand and product, such as COLORSTEEL MAXAM or ZINCALUME, and the colour
- The profile and who rollforms it
- Base metal thickness, for example 0.40 mm or 0.55 mm
- Underlay, flashings and the fastener class for your site
- Full-length sheets, or where any end laps will be
- Scaffolding and edge protection
- The material warranty for your address, and the maintenance it requires, in writing
- For consented work, the LBP doing or supervising it
What you can do, and what to leave
You can
- Hose or gently sponge sheltered areas you can reach from the ground, like soffits
- Look at the spouting from a ladder only if you're comfortable, and book a clean when it's full
- Trim branches that rub on the roof or drop debris onto it
- File the warranty and maintenance schedule where you'll find them
Leave to a roofer
- Anything on the roof itself, including checking fixings
- Replacing sheets, screws and flashings
- Lichen treatment on painted steel, which can damage the paint if done wrong
- Confirming the exposure zone, product and warranty for your address
What we'd put on our own house
For most homes we'd choose a pre-painted steel such as COLORSTEEL MAXAM, in a profile that clears the minimum pitch with room to spare, and we'd care as much about the fixings, flashings and underlay as the colour. Near breaking surf or in a geothermal area, we'd have the product confirmed with the maker before signing. After that, we'd keep up the washing of the sheltered bits, because the warranty depends on it.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.