Match the symptom to the likely cause
| Likely cause | Worth knowing | |
|---|---|---|
| Drips in several spots every time it rains | Screws with hardened or split washers | It's usually roof-wide, so ask for a price on all the screws, not a handful |
| Leaks only when wind drives rain from one side | Dry or gappy sealant at side laps or flashings on that side | Lysaght says infill strips and stop-ends at the rib ends help keep out wind-driven rain |
| A drip below a skylight, flue or air conditioner on a low-pitched roof | Water dammed on the high side of the penetration | BlueScope says penetrations that block the sheet channels on low pitches need a small gutter above them |
| Drips on cold, clear mornings with no rain | Condensation forming under the sheets | Lysaght says foil laminate draped under the sheets acts as a vapour barrier |
| A brown stain spreading from one spot | Rust that has worked through the sheet | Corroded sheets can be fragile, so nobody should stand on them |
| Leaks that started after hail | Overlaps bent out of shape | BlueScope says dents rarely shorten a Colorbond roof's life, but deformed laps can let water in |
Low-pitched and skillion roofs
Metal can run much flatter than tiles. BlueScope says a corrugated profile typically needs at least 5 degrees, while some deeper profiles can go as low as 1 degree. The flatter the roof, the slower water drains, so laps and penetrations have to be right.
The NCC asks for longer end laps on flatter roofs: at least 200 mm where the slope is between 5 and 15 degrees, against 150 mm on steeper roofs. Sheets should run in one length from gutter to ridge wherever possible.
If a newer extension, patio or skillion roof leaks, ask whether the profile suits its pitch. BlueScope says minimum pitch depends on the depth of the profile and how it's fixed, and a sheet laid flatter than it's made for can leak however often it's resealed. Our page on roof sheeting compares the profiles.
Things added to the roof later
A metal roof that was dry for years often starts leaking after something new goes through it: a skylight, a heater flue, an air conditioner, an aerial or solar rails. Each hole needs its own flashing, and BlueScope says skylights and chimneys often need specialist flashing.
How the screws went in matters too. Lysaght says corrugated roofing should always be fixed through the crests, not the valleys of the sheet, to keep it watertight. A rail or bracket screwed down into the pan sits right where the water runs.
Two smaller things show up on older jobs. BlueScope says air conditioner condensate should be piped to the ground rather than left to run onto the roof or into gutters. And metal filings left after drilling rust where they land, so anyone who cuts or drills up there should sweep them off. Our guide to a rusty roof covers what else causes rust.
Two checks before anyone goes up
Grey corrugated roofing on an older house or shed isn't always steel. Corrugated asbestos cement, often called Super Six, was made before 1990 and can pass for metal from the street, so it shouldn't be walked on, drilled or water-blasted until it's been checked. And Safe Work Australia says every roof should be treated as fragile until a competent person says otherwise, naming corroded metal sheets and plastic skylights among the likely culprits. Rusted sheets can give way underfoot, so look from the ground.
What to do when your metal roof leaks
Note when it drips
Rain or no rain, heavy or light, and which way the wind was blowing. Drips on dry, cold mornings change the whole conversation.
Look up from the yard
Use binoculars or a phone's zoom. Rust streaks below screws, a sheet edge curling up, gaps where a flashing meets a wall, or screw heads that look rusty or missing are all worth a photo.
Check for daylight
On a sunny day, look into the roof space from the manhole with the lights off. Pinpricks of light mean holes, usually rust or old screw holes.
List what's been added
Skylights, flues, solar, air conditioning or aerials installed since the roof went on. The leak is often right below one of them.
Book a roofer with the evidence
Share your notes and photos, and ask what they'll use to seal laps and flashings. BlueScope recommends neutral cure sealant on Colorbond, and says sealants that smell of vinegar or ammonia can damage the coating.
What's yours to do, and what isn't
You can
- Recording when it drips and what the weather was doing
- Photographing rust streaks and curled sheet edges from the ground
- Checking for pinpricks of daylight from the manhole
- Asking other trades to sweep up their drilling filings before they leave
Leave to a roofer
- Replacing roofing screws and resealing laps
- Flashing skylights, flues and other penetrations
- Fitting stop-ends or a small gutter above a penetration
- Anything that involves walking on the sheets
What we'd ask the roofer
We'd ask for the cause, not just the patch: which screws, which lap, which flashing, and why it failed. If the leak sits under something added later, we'd ask whether it was flashed properly in the first place. And if the drips only come on cold mornings, we'd ask about condensation before paying for leak repairs. Our guide to condensation or a leak explains the difference.
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.