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.
Before you go up: safety
- Go in the attic in daylight, with someone else in the house who knows you're up there.
- Roofing nails come through the deck overhead. Wear a hat.
- Don't touch wiring, and keep well clear of any old knob-and-tube wiring in older houses.
- In summer an attic can be dangerously hot by midday. Go up early in the morning.
- Never step between the joists. Your foot goes through the ceiling.
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
Most leaks 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. A contractor will usually 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.
Matching the stain to the source
Where the stain shows up in the house narrows the hunt before you even open the hatch:
| Where the stain is | Usual source above it |
|---|---|
| Bathroom ceiling | Pipe boot on the plumbing vent, or a bath fan duct |
| Near the fireplace or a chimney wall | Chimney flashing or a missing cricket |
| Upstairs ceiling near an outside wall, in winter | Ice dam at the eave |
| Inside corner of a room under a roof valley | The valley |
| Room over the garage, along the house wall | Step flashing where the garage roof meets the house |
| Around a skylight | The flashing kit or the curb |
| Many small spots, no rain | Condensation |
While you wait for the repair
- Put a bucket under the drip and towels around it.
- If water is pooling in a bulge in the ceiling, poke a small hole in the center with a screwdriver, over a bucket. The water drains in one place instead of bringing the ceiling down.
- Pull wet insulation aside if you can reach it safely, so the area can dry.
- Photograph everything for your records and for any insurance claim.
- Don't climb onto a wet roof to put a tarp down yourself.
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.
Common questions
Can I track down the leak without going in the attic?
Sometimes, from the ground with binoculars: a cracked pipe boot, a lifted shingle, caulk hanging off the chimney. But many leaks give no clue outside. The water trail is under the deck, so the attic is still the quickest place to look.
Why does my roof only leak in heavy rain?
Light rain runs off normally. Heavy rain, especially wind-driven rain from one direction, pushes water sideways under marginal flashing or up under a lifted shingle. Note the wind direction when it leaks; that tells you which side of the house to check first.
How long does it take?
With a clear water trail in the attic, often a few minutes. Without one, a hose test on the suspected area can take an hour. Leaks that only show in certain storms can take more than one visit to pin down. Keep a simple log of each time it drips, with the date, the weather and the wind direction; after two or three entries a pattern usually appears.
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