How to Find a Roof Leak From Inside the House
The stain is on the ceiling in the hallway. The hole, if there is one, is almost never above it. Water gets in at a detail on the roof, runs down the underside of the decking or along a rafter until it hits a nail or a joint, and drops there. On a 1990s two-story in Parkwood that can be eight feet from the entry point. On a 1930s bungalow in Watts-Hillandale with board decking, it can be the whole width of the house.
You can find the source yourself in about twenty minutes, and it will make the call to a roofer shorter and cheaper. Here's how we do it.
What you need
- A bright flashlight, not your phone
- A tape measure
- Something to kneel on, because the joists are what you walk on, never the drywall between them
- Ideally, rain. Leaks are far easier to trace while they're leaking. If it's dry, wait for the next afternoon thunderstorm or have someone run a hose.
Step one: measure the stain
Before you go up, measure from the ceiling stain to two walls and note which direction the roof slopes above it. Water runs downhill, so the entry point is uphill of the stain — toward the ridge, not the eave. Take those measurements into the attic with you.
Step two: find the trail on the decking
In the attic, find the spot above the stain, then look uphill. What you're looking for on the underside of the plywood or boards:
- Dark streaks running down the slope. A fresh leak is a dark wet line; an old one is a brown stain with a defined edge.
- A shiny nail tip with a drop hanging off it. Water runs along rafters and drips from the first nail it meets.
- Daylight. Turn the flashlight off for a minute. Any pinpoint of light through the deck is a hole, though on board decking a little light at the gaps is normal.
- Rust rings around a nail. That's a nail that's been wet repeatedly — sometimes a leak, sometimes condensation (more on that below).
- Delaminated or fuzzy plywood. Long-term leak. That sheet will need replacing.
Follow the trail uphill until it stops. Where it stops is the entry point. Measure its position from the ridge and from the nearest gable or wall so you can find it from the roof — or so we can.
Step three: match it to a roof detail
Almost every Durham roof leak is at one of six places. Once you know where the trail starts, one of these is usually directly above it.
| Where the trail starts | What it usually is | Typical repair |
|---|---|---|
| Around a round pipe through the deck | Cracked rubber pipe boot | $250 – $450 |
| Beside a chimney | Failed flashing or missing cricket | $600 – $1,500 |
| In a line where two slopes meet | Worn or debris-packed valley | $500 – $1,200 |
| Along a wall where a dormer or upper story meets the roof | Step flashing short, missing or caulked over | $450 – $1,100 |
| Under a square opening in the deck | Skylight flashing kit | $400 – $900 |
| Scattered, near the ridge, on the windward slope | Wind-lifted or creased shingles | $300 – $800 |
A seventh one, specific to the older houses: leaks at the low-slope porch roof where it meets the main wall. Those porches were shingled at 2/12 or flatter and shingles can't hold water on that pitch. That's a re-cover in modified bitumen or a metal pan, $900–$2,500.
Step four: check that it's actually a leak
Two things in a Durham attic look like leaks and aren't.
Condensation. From May to September, humid air in a poorly vented attic condenses on the underside of the deck at night, and in winter warm indoor air does the same on cold decking. The signs: moisture spread across a wide area rather than a trail, rusty nail tips everywhere rather than in one spot, a musty smell, and mold on the north side of the deck. That's a ventilation problem — see our post on roof ventilation problems in Durham attics — and no amount of shingle work fixes it.
A bath fan venting into the attic. Most 1990s builders ran the bathroom exhaust duct to somewhere near a soffit and stopped. Every shower dumps a quart of water into the insulation. The stain shows up above the bathroom and looks exactly like a roof leak. Follow the flexible duct from the fan and see where it ends. If it ends in the attic, that's your leak, and the fix is a roof cap and a proper duct, $250–$500.
What to do with what you found
If you found a pipe boot or a lifted shingle and you're comfortable on the roof, a boot is a hardware-store fix for a handy person. Everything else — flashing, valleys, skylights, anything on a two-story — is worth a roofer, because a flashing job done wrong leaks in the next remnant and takes drywall with it.
Tell us what you found: "trail starts about three feet down from the ridge, about two feet left of the plumbing vent, back slope." That's a $300 repair we can quote before we arrive, instead of an hour of hunting. Our roof repair page has what each repair includes, and if the trail suggests the problem is wider than one spot, the inspection page covers the walked look with a written report.
One more thing: if water is coming through a light fixture or a ceiling fan, turn off that breaker before you do anything else. Then find the leak.
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