Clues to collect before anyone goes up
When does it leak?
Every time it rains suggests a real hole: a cracked tile, rust, or flashing that's failed. Only in a downpour points to something overflowing, like a gutter or valley. Only when the wind blows from one side suggests rain being pushed under a lap or flashing on that side. Cold, dry mornings with no rain at all usually means condensation, not a leak.
Where is the stain?
Draw a rough plan of the house and mark the stain on it. Then picture the roof above: is the mark under an inside corner, a chimney, a skylight, the ridge line or an outside wall? The table below shows what each spot usually means.
What changed recently?
Leaks that start a few weeks after other trades were on the roof are common, because tiles crack underfoot. Think back to solar, aerials, air conditioning, a storm or hail, or a tree that's grown over the roof.
Shine a torch from the manhole
On a bright day, lift the manhole cover and look without climbing in. Daylight through a gap, dark streaks on timber or a damp patch of insulation can lead you close to the spot.
Watch it happen
In the next heavy rain, look out a window or from under the porch. Which gutter spills over? Does a valley overflow sideways? Is a downpipe gushing at a joint? Film it, because the roofer may be standing on a dry roof when they come.
What the stain's position usually points to
| Usual suspect | What to look for from the ground | |
|---|---|---|
| Under an inside corner where two roof slopes meet | A valley that's blocked, rusted or overflowing | Leaves piled in the channel, or water spilling sideways in rain |
| Below a chimney, skylight, flue or vent | Flashing that's lifted, rusted or pulled out of its joint | Rust streaks, gaps, or flashing standing away from the roof |
| Along an outside wall or above a window | A gutter overflowing back under the roof edge | Water pouring over the back of the gutter in heavy rain |
| In a line under the peak of the roof | Cracked ridge mortar or loose caps | Caps out of line, or crumbs of mortar in the gutters |
| Near or under solar panels | A cracked tile or badly sealed mount from the install | Tiles out of line around the array |
| Spots scattered across several rooms | Condensation, or a roof failing in many places | Marks turning up on cold mornings without rain |
Before you look in the roof space
Stay on the ladder at the manhole and look with a torch. Ceiling plasterboard won't take your weight, and one slip between the joists puts a foot through the ceiling, or worse. Don't touch wiring, and keep clear of foil sarking or foil insulation near cables, because Your Home warns foil conducts electricity. In a house built before 1990, leave any loose, fluffy fill between the joists alone: some older homes used loose-fill asbestos as ceiling insulation. If water is anywhere near light fittings, turn the power off at the switchboard first.
Is it even the roof?
Plenty of so-called roof leaks turn out to be something else. A hot water service in the roof space, a ducted air conditioner's drain line, a shower upstairs or a leaking pipe can all mark a ceiling. If the stain grows on dry days, call a plumber before a roofer.
Air conditioners deserve a second look. BlueScope says condensate from them should be piped to the ground, not into gutters, so a drain line dumping water onto the roof or into a gutter is worth mentioning when you call.
How the roofer takes it from here
Your clues get the roofer to the right part of the roof. From there they check the roof space properly, then the roof above and uphill of the stain, because water runs downhill along battens and sarking before it drops.
If the leak still won't show itself, they may run a hose over one section at a time while someone watches inside. That needs a person on the roof, so it's never a DIY test. Our page on roof leak detection explains the methods and what they cost.
What you can work out, and what you can't
You can
- The timing pattern, from a simple log of each leak
- Where the stain sits relative to valleys, chimneys and walls
- Overflowing gutters and spilling valleys, watched from the ground in rain
- Daylight or wet timber, seen from the manhole with a torch
- Recent work on the roof by other trades
Leave to a roofer
- The exact spot where water gets in
- Hose testing, one section at a time
- Lifting tiles or sheets to see underneath
- Moisture meter and thermal camera readings
- Anything on an older roof that might be asbestos
Where we'd start
We'd spend one rainy evening watching and one dry morning looking. Mark the stain on a rough sketch of the house with the valleys, chimney and skylights drawn in, and note when each leak happened. Hand that to the roofer and you'll often save them time up top, which is a big part of what a leak call-out costs. Our leak finder quiz turns your answers into a likely cause.
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.