Roof screws that are pulling out or corroding are one of the most common causes of leaks in New Zealand's metal roofing systems. Catching the problem early — before water gets in — can save you thousands in repairs. Here's how to inspect your roof screws safely and know what to look for.
Safety First Before You Go Up
Working at height is one of the leading causes of serious injury in New Zealand. Before you climb onto your roof, read WorkSafe NZ's guidance on working at height and consider whether the job is better left to a professional. At minimum:
- Use a sturdy, correctly rated ladder secured at the base and top
- Wear non-slip footwear
- Never work on a wet, frosty, or windy roof
- Let someone know you're going up
- Avoid walking directly on the roofing sheets — step on the purlins (the structural supports beneath) where possible
If your roof pitch is steep (generally above 25°) or you're not confident at height, do not attempt this inspection yourself.
What Are Roof Screws and Why Do They Fail?
Most New Zealand homes with metal roofing (corrugate, tray, or standing seam profiles) use self-drilling roofing screws with a neoprene or EPDM rubber washer to create a weathertight seal. Over time, two main failure modes occur:
- Corrosion: The screw or its washer degrades, allowing water ingress
- Pull-out: The screw loses grip in the purlin or batten below, leaving the sheet loose
NZ's coastal salt air, UV exposure, and frequent wet-dry cycles accelerate both problems. BRANZ research consistently identifies fastener failure as a key contributor to roof leaks in NZ housing.
How to Inspect for Corroding Screws
Visual Check from Ground Level
Start with binoculars from the ground or a ladder at eave height. Look for:
- Orange or brown rust streaks running down the roof from screw heads
- White or grey chalky deposits around screw heads (galvanic corrosion)
- Missing screw caps or exposed bare metal around fastener points
- Screws that appear to have sunk into the sheet or left a dark stain ring
Close-Up Inspection on the Roof
If it's safe to get closer, examine individual screws for:
- Washer condition: A healthy neoprene washer sits flat and is slightly compressed. A failed washer looks cracked, shrunken, hardened, or completely missing
- Screw head corrosion: Surface rust on a zinc or painted head is a warning sign; a screw that crumbles when touched needs immediate replacement
- Hole elongation: If the hole around the screw has stretched or torn, water is almost certainly getting in
- Sealant breakdown: Some older installations used silicone around screws — check if it has cracked or pulled away
| Screw Condition | Risk Level | Action |
|---|---|---|
| Head intact, washer flat and flexible | Low | Monitor annually |
| Surface rust, washer slightly hard | Medium | Plan replacement soon |
| Heavy rust, cracked or missing washer | High | Replace promptly |
| Screw head missing or crumbled | Critical | Call a roofer immediately |
How to Check for Screws Pulling Out
Pull-out happens when the screw thread strips the timber purlin or batten below — often due to the timber drying and shrinking over time, or because the wrong screw length was used originally.
Signs to look for:
- Raised screw heads: A screw sitting proud of the sheet surface (rather than flush) has likely lost grip
- Sheet movement: Gently press down near a screw — if the sheet flexes noticeably or you can hear a creak, the fastener isn't holding
- Visible gaps: Lifted sheet edges or ridgelines where the profile has separated from the purlin below
- Interior evidence: Water stains on ceiling lining directly below a fastener line, or daylight visible from the roof space, are strong indicators
Check your roof space on a bright day with the lights off — any pinpricks of light around fastener areas confirm a problem.
NZ-Specific Considerations
New Zealand's NZS 3604 (Timber-framed buildings) and the NZ Building Code clause E2 (External Moisture) set requirements for weathertightness, including roofing fasteners. Screw type and spacing must suit the roofing profile, purlin spacing, and local wind zone. If your home is in a high wind zone (common in Wellington, Marlborough, and exposed coastal areas), fastener pull-out is a more serious structural risk — not just a leak issue.
For coastal homes within 500 metres of the sea, BRANZ recommends stainless steel or high-grade coated fasteners to resist salt corrosion. Standard zinc-plated screws can fail within a few years in these environments.
When to Call a Professional
Contact a qualified roofer if you find:
- More than a handful of corroded or pulled-out screws (widespread failure often means a full re-screw is needed)
- Any signs of sheet lifting, especially near ridges or edges in a high wind zone
- Active leaks or water staining inside the home
- A roof over 15–20 years old that has never had a fastener inspection
- You're not comfortable working at height
A professional roofer can re-screw the entire roof with correctly rated fasteners, often without needing a building consent (though always confirm with your local council for your specific situation — see MBIE Building Performance for Schedule 1 exemption guidance). You can find qualified local roofers on tradedirectory.co.nz.