A small leak in a metal roof can quickly turn into a big headache if left untreated — water damage, mould, and structural rot can all follow. The good news is that many minor leaks on corrugated iron or long-run steel roofs are within reach of a capable DIYer, as long as you work safely and know your limits.
Safety First: Working at Height
Before you grab a ladder, understand that working on a roof carries serious fall risks. WorkSafe NZ considers falls from height one of the leading causes of serious injury in New Zealand. Always:
- Use a sturdy, properly footed ladder rated for your weight
- Work with a helper who can steady the ladder and assist
- Wear non-slip footwear and avoid working in wet or windy conditions
- Use a roof ladder (chicken ladder) hooked over the ridge to spread your weight and avoid slipping
- Never work alone at height
If the roof pitch is steep, the leak is near the ridge, or you're not confident, stop and call a professional.
Find the Source of the Leak
Leaks are sneaky — water often travels along rafters or purlins before dripping inside, so the wet patch on your ceiling may not be directly below the entry point. To track it down:
- Inside first: On a dry day, go into the roof space with a torch and look for water stains, rust marks, or daylight showing through.
- Outside inspection: Walk around the house and visually scan the roof from ground level with binoculars before climbing up.
- Common culprits on NZ metal roofs include:
- Deteriorated or missing lap sealant at sheet overlaps
- Cracked or dried-out flashing around chimneys, skylights, and penetrations
- Loose or missing roofing screws (often the fastener washer has perished)
- Rust holes or corrosion on older Zincalume or painted steel
- Blocked gutters causing water to back up under the roof edge
Tools and Materials You'll Need
| Item | Purpose |
|---|---|
| Roof ladder / chicken ladder | Safe access on the slope |
| Wire brush | Clean rust and debris from repair area |
| Rag and solvent (e.g. methylated spirits) | Degrease surface before sealing |
| Roofing sealant / lap sealant | Seal overlaps and small gaps |
| Butyl or polyurethane roofing tape | Patch small holes or cracks |
| Replacement roofing screws with neoprene washers | Replace failed fasteners |
| Rust-inhibiting primer and touch-up paint | Treat any corrosion |
| Safety gear | Gloves, non-slip boots, safety glasses |
Products like Sika roofing sealants and butyl-based flashing tapes are widely available at Mitre 10 and Bunnings. Match your touch-up paint to your existing roof colour — Resene and other suppliers can colour-match if needed.
Step-by-Step: Fixing Common Small Leaks
Replacing a Leaking Roofing Screw
- Remove the old screw with a drill or screwdriver.
- If the hole is slightly enlarged, use a slightly larger screw with a fresh neoprene washer, or fill the old hole with sealant before inserting the new screw.
- Do not overtighten — the washer should compress slightly, not be crushed flat.
Sealing a Lap or Flashing
- Clean the area thoroughly with a wire brush and solvent — sealant won't bond to dirty or oily surfaces.
- Apply a roofing-grade sealant or butyl tape into the overlap or gap.
- Press firmly and smooth with a gloved finger or putty knife.
- Allow to cure fully before rain (check the product's instructions).
Patching a Small Rust Hole
- Wire-brush all loose rust back to sound metal.
- Apply a rust-inhibiting primer and allow to dry.
- Apply a self-adhesive roofing patch tape (butyl or aluminium-backed) over the hole, pressing out any air bubbles.
- Seal the edges of the patch with roofing sealant.
- Touch up with compatible roof paint to protect the repair.
Choosing the Right Sealant
Not all sealants are suitable for metal roofs. Look for products specifically labelled for metal roofing or flashings. Avoid standard silicone in laps — it can actually trap moisture. Polyurethane and butyl-based products generally perform better in NZ's variable climate, from the UV-intense summers to wet West Coast winters.
When to Call a Professional
Some situations are best left to a licensed roofer:
- Widespread rust or corrosion — may indicate the roof is nearing end of life
- Flashing around chimneys, skylights, or penetrations — complex to seal correctly and critical to the NZ Building Code's weathertightness requirements (refer to MBIE Building Performance for guidance)
- Leaks you cannot locate — a roofer can do a hose test or thermal inspection
- Steep or high roofs — fall risk is too great for most homeowners
- Any work involving structural roof members — this may be Restricted Building Work under the Building Act, requiring a Licensed Building Practitioner (LBP)
For peace of mind, find a qualified local roofer on tradedirectory.co.nz who can assess the full condition of your roof and carry out repairs to a professional standard.
A Note on Older NZ Roofs
Many New Zealand homes still have roofs clad in older unpainted galvanised iron or early Zincalume, which can be more prone to corrosion. BRANZ research highlights that regular maintenance — clearing debris, checking fasteners, and repainting when the surface starts to chalk or rust — significantly extends roof life. A small repair done promptly is almost always cheaper than a full re-roof later.