Roof screws are one of the most common sources of leaks on New Zealand metal and corrugated roofing — and one of the easiest things to overlook during routine maintenance. The good news is that a basic visual inspection is something most homeowners can do safely from the ground or a ladder, and catching a failing screw early can save you from costly water damage inside your home.
Understanding How Roof Screws Work
Most metal roofing in NZ — including corrugated iron, long-run steel, and Colorsteel profiles — is fixed with self-drilling hex-head screws fitted with a neoprene or EPDM rubber washer. When driven correctly, the washer compresses slightly to form a watertight seal around the hole. Over time, UV exposure, thermal cycling (the roof expanding and contracting with temperature changes), and physical wear cause these washers to harden, crack, or deform — breaking the seal and allowing water to track down the screw shank and into your roof space.
Safety First
Before you go anywhere near your roof, take a moment to plan your approach. Falls from roofs are a leading cause of serious injury in New Zealand — WorkSafe NZ has clear guidance on working at height. Use a stable ladder rated for your weight, wear rubber-soled footwear, and never work on a wet or frosty roof. If your roof pitch is steep (generally over 25°) or you are not confident working at height, arrange for a qualified roofer to carry out the inspection instead.
What to Look For: A Step-by-Step Inspection
1. Start From the Ground
Using binoculars on a bright day, scan the roof surface for obvious signs of trouble:
- Rust staining running down from screw heads
- Missing screw caps or heads that appear raised or tilted
- Discolouration or bubbling of paint around a screw
- Visible gaps between the washer and the roofing sheet
2. Check the Roof Space After Rain
Before going onto the roof, head into your ceiling space with a torch after a decent rainfall. Look for:
- Water stains or drips on the underside of the roofing or on the sarking/underlay
- Rust streaks tracking down from fixings
- Wet insulation directly below screw lines
This can help you pinpoint problem areas before you climb up.
3. Close-Up Inspection on the Roof
If it is safe to access the roof, inspect each screw (or a representative sample) for the following:
| Issue | What to Look For | Risk Level |
|---|---|---|
| Compressed/cracked washer | Washer is flat, brittle, or split | High — likely leaking |
| Over-driven screw | Washer is squashed right out beyond the head | High — seal is broken |
| Under-driven screw | Head sits proud, washer not compressed | Medium — may not be sealing |
| Corroded screw | Rust around the head or shank | Medium to High |
| Tilted or backed-out screw | Head is angled or rising up | High — hole may be enlarging |
| Missing screw | Empty hole visible | High — open penetration |
Gently press each washer with your finger — a healthy washer should feel slightly springy and pliable. If it feels rock-hard, crumbles, or has visible cracking, it needs replacing.
4. Check Screw Placement
Screws should be driven into the crown (top) of the corrugation, not into the pan (the low point where water flows). Screws in the pan are far more likely to leak. This is standard practice under good roofing trade guidelines and aligns with manufacturer installation requirements.
How Old Is Too Old?
Neoprene washers typically last 10–20 years depending on UV exposure and climate. In harsher NZ coastal or high-UV environments (think Northland, Nelson, or Canterbury's nor'west conditions), degradation can happen faster. If your roof is more than 15 years old and has never had the screws checked, it is well worth a thorough inspection.
DIY Repairs: What You Can Do
Replacing individual failed screws is generally within the scope of a competent DIYer, provided safe roof access is possible. You can purchase replacement roofing screws with new washers from Bunnings or Mitre 10 — match the screw length and diameter to your existing fixings, and choose a screw with a compatible coating (e.g. Class 4 galvanised or stainless for coastal areas).
For a leaking hole that has enlarged (common when a screw has been backing out for a while), a simple replacement screw may not grip. In this case, a roofer may use a larger-diameter screw, a screw with a bonded washer, or apply a compatible roof sealant — check with your roofing sheet manufacturer for approved products.
Do not use standard silicone as a long-term fix on metal roofing — it can degrade quickly and may not be compatible with your roofing coating. BRANZ is a good resource for understanding what products are appropriate for NZ roofing systems.
When to Call a Professional
Contact a qualified roofer if:
- You are not confident working safely at height
- Multiple screws across the roof are failing — a full re-screw may be more cost-effective
- You find enlarged or damaged holes that need more than a simple screw swap
- There is evidence of widespread rust or coating failure on the roofing sheets themselves
- Your roof is under warranty — DIY repairs may void manufacturer or installer warranties
A licensed roofer can also advise whether your roof meets current requirements under the NZ Building Code clause E2 (External Moisture), particularly if you are planning any alterations. Check MBIE Building Performance for guidance on when building consent may be required for roofing work.
You can find qualified local roofing tradespeople on tradedirectory.co.nz.
Roofing Association of NZ (RANZ)
Licensed Building Practitioner (LBP)
.png)
