Why are some leaks so hard to find?
Water gets in at one point, then follows whatever it lands on. It slides down sarking, along a batten or a rafter, and drops wherever the timber dips. The damp patch inside can end up a fair way from the cause.
Some leaks need a particular mix of conditions: rain pushed up under a lap by wind from one direction, or a downpour heavy enough to overflow a valley. On a calm day with a hose, they behave themselves.
Which methods do roofers use, and what can't each do?
| What it finds | Where it falls short | |
|---|---|---|
| Roof space check | Stained timber, wet insulation, daylight through gaps | Needs safe access, and low pitches or deep insulation hide a lot |
| Close look on the roof | Cracked tiles, failed flashing, loose screws, clogged valleys | Hairline cracks and gaps under laps are easy to miss |
| Hose testing | Recreates the leak, one section of roof at a time | Slow, and hard to mimic wind-driven rain |
| Moisture meter | Damp timber or plasterboard, to trace the wet path back | Shows where it's wet, not where the water got in |
| Thermal camera | Cooler damp patches in ceilings and roof surfaces | Depends on the weather and time of day, and needs someone who can read it |
What does a proper detection visit look like?
Before going up, the roofer should ask when it leaks, look at the stain and get into the roof space if that's safe. Your notes and photos save them time, and you money.
Hose testing takes two people, one on the roof and one inside watching. Each section gets soaked and then left long enough to show itself before moving on, so it isn't quick. Starting low and working uphill stops water from higher up muddying the result.
By the end you should have the cause, photos of it, and a price to fix it. If they can't pin it down on the day, they should tell you what they've ruled out and what they'd try next.
Helping the roofer find it faster
You can
- Keep a leak diary: date, time, how hard it rained and which way the wind blew
- List anything that changed up top recently, like solar panels, an antenna, a new air conditioner or a skylight
- Clear the cupboard or hallway under the manhole so the roofer can get straight into the roof space
Leave to a roofer
- Hose testing, which needs someone working on the roof
- Moving around the roof space, where one wrong step goes through the ceiling
- Using moisture meters and thermal cameras, and reading the results
- Lifting tiles or sheets to see what's underneath
How we'd approach it
For a leak that's already beaten one roofer, we'd book a proper detection visit with a hose test, priced by the hour or as a set fee agreed up front. Hand over your leak diary. A roofer who finds the real cause once is cheaper than three who each guess and patch.
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.
