Why nails pop and screws fail
Many older iron roofs were nailed down. Steel sheets expand in the sun and shrink at night, and the timber purlins underneath dry out, swell and move with the seasons. Over years, that movement works nails loose until the heads stand proud of the iron, and every lifted nail is a hole for water. Manufacturers allow for the same movement on long sheets: NZ Steel's conditions for COLORSTEEL ALTIMATE, for example, call for oversized fastener holes on sheets over 10 m long.
Screws hold better, but they fail too. The sealing washer under each head breaks down in the sun over time, an overdriven screw crushes its washer, and one left loose never seals at all.
Fixings rust as well, and near the sea or on unwashed parts of the roof they can go before the sheets do. NZ Steel's COLORSTEEL warranty covers the roofing material only, not the fasteners, and excludes damage from failing to replace corroded fasteners.
The wrong fixing can cause the damage
Metals react with each other. NZ Steel says stainless steel fasteners shouldn't be used with ZINCALUME in any environment, lead-headed nails must not be used, and sealing washers should be low carbon and non-conductive. It also warns that lead or copper fasteners dramatically speed up corrosion of the zinc on galvanised steel when it's damp.
Fixings also need to suit how exposed the house is. Dimond says exposed roofing fasteners should be at least Class 4, and Class 5 in Very Severe environments. The metal roofing Code of Practice sets a minimum exposed fastener class of C4 for zones B to D, C5 for zone E and C6 for zone F. Under the Acceptable Solution E2/AS1, hot-dip galvanised nails are only acceptable exposed in zones B and C.
You don't need to remember any of that. Just ask the roofer what screw and washer they'll use, and whether it suits your exposure zone and the roofing manufacturer's requirements.
Signs your fixings are letting go
- Nail heads standing proud of the iron, visible from the ground with binoculars
- Rust streaks running down from fixings
- Small rust rings around screw heads
- Drips or stains on the ceiling in a neat row
- Iron rattling or lifting at the edges in wind
- Tiles that have slipped or lifted after a storm or an earthquake
Leave the hammer on the ground
Banging popped nails back down is a job people try from a ladder or the roof. Please don't. It puts you on iron that may be slippery or brittle, and a nail driven back into a worn hole usually lifts again. WorkSafe says even short jobs at height that take minutes still need fall prevention and a risk assessment, and NZMRM says it must never be assumed that it's safe to stand on any roof.
How a roofer fixes it
On an iron or longrun roof, the usual fix is to pull lifted nails and replace them with roofing screws and new washers, sized so they bite into sound timber. A roofer will check the purlin under the worst spots, deal with any holes that have worn oversized, and replace screws with perished or crushed washers.
A careful roofer sweeps or hoses off swarf (the steel filings from drilling) as they go, because it rusts on the roof and NZ Steel's COLORSTEEL warranty doesn't cover damage from swarf left behind.
On concrete or clay tile roofs, the fixings are the ties, clips or nails holding tiles to the battens. E2/AS1 calls for 304 or 316 stainless steel tile fixings in exposure zones B to E, or hot-dip galvanised fixings in zones B and C. BRANZ's look at Christchurch houses after the Canterbury quakes found loose or corroded tile ties were a big reason heavy tiles ended up off their battens in the hill suburbs. The Natural Hazards Commission suggests checking that tile fixings aren't loose, rusted or broken.
Refix, or re-roof?
Refixing makes sense when the iron is sound and the fixings are the only problem. It's repair and maintenance with comparable products, so it doesn't usually need a building consent under Schedule 1, and it doesn't usually need an LBP, which is for restricted building work such as a consented re-roof.
If the iron around the nail holes has rusted, the laps are failing, or nails are lifting across the whole roof, new screws in old iron won't hold for long. That's the point where a re-roof starts to make more sense than chasing fixings. Our guide on repainting or re-roofing an iron roof helps with that call.
What to do if you spot popped nails
Photograph them from the ground
Use binoculars or a phone zoom, and note roughly where they are on the roof.
Check the ceiling and roof space after rain
Look for drips or stains lined up under a row of fixings. Step only on the joists in the roof space.
Listen on a windy day
Rattling or banging iron means sheets are moving, and loose iron is what wind gets under in a storm.
Get a roofer out before the next big blow
Ask whether they'd replace only the lifted nails or refix the whole roof, and why.
Ask for before and after photos
It shows you what was replaced without you going anywhere near the roof.
Keep the invoice
It's part of your maintenance record, which matters for product warranties and for showing an insurer the roof has been looked after.
Your part, and the roofer's
You can
- Spot lifted nails and rust streaks from the ground
- Check the roof space after heavy rain
- Keep dated photos so you can see if it's getting worse
- Keep branches trimmed back so they don't rub or drop onto the iron
- Make sure nobody hammers nails back in from a ladder
Leave to a roofer
- Replacing nails and screws with the right fixings for your zone
- Checking purlins and battens under the worst spots
- Refixing or replacing tile ties and clips
- Clearing swarf and checking for scratches
- Deciding whether the iron is worth refixing at all
Questions to ask before a roofer refixes your roof
- Will you replace every nail, or only the lifted ones, and why?
- What screw and washer will you use, and does it suit my exposure zone?
- Will you check the purlins or battens under the worst spots?
- How will you clear swarf as you go?
- Is the iron sound enough to be worth refixing?
- Can you send photos before and after?
What we'd do about popping nails
If it's a handful of popped nails on sound iron, we'd have a roofer swap them for screws soon, before a storm gets under a loose sheet. If nails are lifting everywhere and the iron around them is rusty, we wouldn't pay for a full refix. We'd put that money towards a re-roof instead.
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.