How to Find a Roof Leak From Inside the House
The stain is in the hallway ceiling. The leak is almost never above the stain. Water gets under a shingle, runs along the top of the underlayment, drips onto a rafter, follows the rafter downhill and lets go wherever it feels like. On a 6/12 roof, the entry point can be eight feet uphill from the drip. That's why the first tool for finding a roof leak in Des Moines is a flashlight, not a ladder.
What you need
A bright flashlight, a phone for photos, a tape measure, and a dry day followed by a wet one. Old clothes. If your attic is the crawl-in kind common on 1920s–40s houses in Beaverdale and Drake, a dust mask and a board to lie on. Walk only on the joists or the board, never on the drywall between them.
Step 1: Map the stain
Before you go up, measure where the stain is on the ceiling from two walls. Note which way the roof slopes above it. In the attic, find that spot and start looking uphill from there, toward the ridge.
Step 2: Look for the water trail
On the underside of the roof decking you're looking for:
- Dark streaks running down a rafter or across the plywood. Old ones are gray-brown; active ones are darker and may still be damp.
- Rust-colored rings around a nail tip or a spot on the decking.
- Wet or matted insulation below the trail. Push a finger in.
- Daylight. Turn the flashlight off. Any pinpoint of light through the deck is a hole.
- Mold or delaminated plywood — a sign the leak has been there a while.
Follow the trail uphill until it stops. Where it stops is where the water is coming in. Photograph it and measure from the nearest gable wall or chimney so you can find it from the top.
Step 3: Check the usual suspects
Nine leaks in ten on Des Moines houses start at one of these, and each has a signature from inside.
Pipe boots. Look for a plumbing vent pipe coming up through the deck. The rubber collar on the roof side cracks after 10–15 years, and the trail starts right at the pipe. Stain is usually near a bathroom or the kitchen. Repair: $250–$450.
Chimney. On the old brick chimneys around Highland Park and Union Park the flashing has been caulked a dozen times. From inside, the trail starts at the uphill side of the chimney where the cricket should be. Repair: $600–$1,500.
Valleys. Where two roof planes meet. The trail starts along the line of the valley. Common on the cut-up 2000s roofs in Ankeny and Johnston where the valley was laid without membrane. Repair: $500–$1,200.
Walls and dormers. Water comes in where the roof meets a vertical wall — a dormer, a second story over a garage, an addition. The trail starts at the wall line. Usually missing or short step flashing. Repair: $450–$1,100.
Skylights. The trail starts at a corner of the curb. It's the flashing kit far more often than the glass. Repair: $400–$900.
Eaves, in winter only. If the stain is near an exterior wall and shows up in February, look at the bottom three feet of the deck. Water pushed under the shingles by an ice dam comes in there. That's an ice dam, and the fix is in the attic, not on the roof.
Step 4: Confirm it with a hose
If you found a trail but aren't sure of the entry, wait for a dry day. One person in the attic with the flashlight, one on the roof with a garden hose — or on a ladder at the eave if the roof is steep. Run the hose gently on one section at a time for a few minutes, starting low and working uphill, staying on one side of the suspected spot. Don't spray uphill under the shingles; that fakes a leak that doesn't exist. When water appears inside, you've found it.
If you aren't comfortable on the roof, don't go. A wet 8/12 roof on a two-story is not worth a $400 repair. We do the hose test as part of a leak repair visit.
When it isn't a leak
In central Iowa, a lot of "leaks" reported between December and March are not leaks:
- Frost on the nails. Warm, wet household air gets into the attic, freezes on the nail tips, and melts on the first sunny day. Hundreds of little drips at once, then nothing until the next cold snap. The fix is air sealing and venting the bath fans outside.
- Condensation on the deck on a house with no soffit vents and a lot of insulation blocking what's there.
- A bath fan duct that runs across the attic and drips at a low point.
If the drips appear only after cold nights, with no rain, read roof leak or condensation before you spend money on shingles.
What to tell the roofer
Where the stain is, when it appears (every rain, only heavy rain, only in winter), what you found in the attic, and your photos. That turns a two-hour hunt into a twenty-minute one, and the price follows.
Need roof work in Des Moines?
Call for a free estimate. Mon–Sat 7am–7pm.