How to Find a Roof Leak From Inside the House
The stain on the ceiling is almost never under the hole in the roof. Water comes through the shingles, hits the decking, runs along a rafter until it finds a nail or a seam, and drops onto the drywall two, six or fifteen feet from where it started. So the first place to look for a roof leak isn't the roof. It's the attic, with a flashlight, ideally while it's raining.
What you'll need
- A bright flashlight, not your phone
- A tape measure
- A pencil or chalk
- Boards to kneel on if the attic has no floor — stepping between the joists puts your foot through the ceiling
- Someone below with a phone to text you when you're over the stain
Go up during or right after a good rain if you can. A dry attic still shows the history, but a wet one shows you where the water is coming in today.
Step one: find the wet spot from above
Measure the stain's position from two walls in the room below, then find the same spot in the attic. Look at the insulation there — is it damp, matted, or discolored? Pull it back. You're looking for the underside of the roof decking, and you're looking for water.
Step two: follow the trail uphill
Water runs downhill along the rafters and the underside of the deck. From the wet spot, look up-slope. You'll see a dark streak on the wood, sometimes with a tide line where it's dried repeatedly, sometimes with white mineral deposits or black mold spotting. Follow it up until it stops. Where it stops is where the water is entering. Mark it with chalk and measure its position from the ridge and from the nearest gable wall so you can find it from the roof.
On the 1960s ranches around 87th and Antioch, the deck is often 1-by-6 planks with gaps between them, so the trail hops from board to board; on the 1990s OSB decks south of I-435, it runs cleanly along the sheet seams.
Step three: look for what interrupts the roof
The entry point is almost always at something that breaks the shingle field. Stand under the chalk mark and look around within about six feet:
A pipe. Plumbing vents come through the roof above every bathroom and the kitchen. The rubber boot around the pipe cracks with age and Kansas sun, and the leak shows up beside the pipe. A very common source on Overland Park roofs. $250–$450 to fix.
The chimney. If the trail leads to the chimney, the flashing has failed. On brick chimneys on older Johnson County homes it's usually the caulked-on aluminum strip letting go. Look for staining on all four sides of the chimney framing.
A valley. Two slopes meet, and the trail runs up into the seam. Worn-through shingles or a rusted valley metal.
A wall. The garage roof meets the second-story wall, or an addition meets the main house. Step flashing is short, missing or was never installed. You'll see staining along the whole length of the wall line.
A skylight. Trail leads to a framed rectangular opening. Usually the flashing kit, sometimes a failed seal in the unit.
Nothing at all. Trail leads to the middle of a slope with nothing near it. Look for a nail poking through the deck with rust around it — a nail that missed the rafter and backed out through the shingle. Or a hail crack directly above. Or, if it's winter and the staining is diffuse and frosty rather than a streak, it may not be a roof leak — see the last section.
Step four: the hose test, if you're stuck
If the trail is ambiguous, wait for a dry day. One person in the attic with the flashlight, one on the roof with a garden hose. Start low on the slope near the suspected area and run water for a few minutes on one section at a time, working uphill. Don't spray up under the shingles; let it run down like rain. When the attic watcher sees water, you've found it. This takes 30 minutes and finds almost everything that a walk didn't.
Reading the stain itself
The ceiling stain carries clues even before you go up. A brown ring with a darker edge has dried and re-wet several times, so the leak is old. A soft, wet patch with no ring is new. A stain at the top corner of an exterior wall points to the eave, often ice backing up in winter. Stains that only show after snow melts, not after rain, also point to ice at the eaves. Stains that only show in wind-driven rain often lead to flashing at a wall or a chimney, where water is pushed sideways.
Leaks that aren't the roof at all
Not every drip in an attic comes through the shingles:
- An air-conditioning drain line in the attic can clog or crack and drip in summer, often right over a hallway.
- A bath fan duct carrying warm, damp air can sweat and drip if it isn't insulated.
- A plumbing vent joint below the roofline can leak when the pipe is used.
- A window or siding leak on a wall above a lower roof can show up inside and look like a roof problem.
If the trail leads to one of these, you need a different tradesperson, and the roof can be crossed off.
When to call a roofer
If the trail leads to flashing, a valley, or a spot you can't reach safely, it's time. Bring the measurements, the photos and your notes. Those three things often turn a long search into a short visit.
Safety in the attic
Attics are hot in summer and awkward all year. Go up in the morning in warm months, and take water. Step only on joists or on boards laid across them, never on the drywall between. Watch for nails coming through the deck above your head. Keep clear of wiring, and don't disturb old insulation more than you need to; wear a dust mask and gloves.
Keep a leak log
Write down the date, the weather, the wind direction if you know it, and where the water showed up, with a photo each time. Two or three entries usually point at the cause. A leak that only appears in a southwest wind is a very different repair from one that appears in every rain.
What not to do
- Don't caulk the hole from the attic side. Water will still get into the deck and rot it; you've just moved the drip.
- Don't spray foam it. Same problem, harder to fix later.
- Don't ignore a small drip because it's winter. Every freeze-thaw cycle between now and March widens the gap.
- Don't walk on a wet or icy roof. The roof repair page covers repair options once you've narrowed it down; you don't need to go up.
When it isn't a roof leak
Some winter "leaks" in Overland Park attics are condensation. Warm, humid air from the house — especially from a bathroom fan that dumps into the attic instead of outside, which is common on 1970s ranches — hits the cold underside of the deck, frosts, and then drips during a warm spell. The signs: staining spread across a whole area rather than a streak, frost on the nail tips in January, and drips that happen on sunny days after cold nights rather than during rain. That's a ventilation and air-sealing job, not shingles. Roof ventilation Overland Park attics need is intake at the soffit and exhaust at the ridge, and a bath fan ducted out through the roof or gable.
If you found the spot, send the roofer the chalk-mark measurements and a photo when you ask for an estimate. If you didn't, that's fine too — tracing it from the attic is usually the first thing a roofer does on a leak. Repair and replacement estimates from local roofers are usually free; a formal written inspection report typically runs $150–$300. Ask whether the fee is credited if you hire that roofer.
Need roof work in Overland Park?
Call for a free estimate. Mon–Sat 7am–7pm.