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 down a rafter or a truss chord for six or eight feet, and drops onto the drywall wherever gravity finally wins. So the first step in finding a roof leak is to stop looking at the ceiling and get into the attic. Here's how we do it, and how you can do most of it yourself before you call.
What you need
A bright flashlight, a phone for photos, a dust mask, and a tape measure. Wear long sleeves — Maple Grove attics are full of blown fiberglass or cellulose. Step only on the truss bottom chords or joists, never on the drywall between them. If the attic hatch is in a closet, pull the clothes out first; you'll be dragging insulation.
Go during or just after rain if you can. A dry attic on a sunny day tells you where water has been, not where it's coming from now.
Step 1: find the stain from above
Measure from two walls to the center of the ceiling stain, then find the same spot in the attic. Look at the insulation there — it will be damp, matted or discolored — and then look up. You're looking for the water trail: a dark streak on the underside of the decking, running downhill from somewhere higher. Follow it uphill with the light. The entry point is at the top of the streak, and it's usually within a few feet of one of the things below.
Step 2: check the usual suspects
Nine out of ten leaks in the 1980s–2000s homes across Maple Grove come from one of these:
Pipe boots. The rubber collar around every plumbing vent stack. The stain lands near a bathroom or the kitchen. From the attic you'll see a dark ring on the decking around the pipe. Freeze-thaw and UV crack them at 10–15 years.
Chimney flashing. A dark stain on the decking uphill of the chimney, or water marks down the chimney framing. Common on the brick chimneys of the 1980s two-stories around Fish Lake and along Zachary Lane, which were often flashed with one caulked strip of aluminum.
Valleys. Water trail running the length of the valley from above. On a 25-year-old roof the shingles there are worn through.
Skylights. Stains at the corners of the skylight well. Usually the flashing kit, not the glass.
Roof vents and attic fans. Box vents crack, and the flashing flange on a powered attic fan rusts.
Wall flashing. Where a lower roof meets a wall — the garage roof against the second story, or a three-season porch off the back — water runs down the siding and behind short step flashing.
The eaves. A stain in a line along the top of an exterior wall, on the north side, that appears in February or March, is ice dam water backing up under the first courses. It's a different problem with a different fix, and our ice dam page covers it.
Step 3: rule out the leaks that aren't leaks
This is the step most homeowners skip, and in Minnesota it matters more than anywhere. Two things drip in an attic without any hole in the roof:
Condensation. Warm, moist air from the house gets into the attic through can lights, the hatch, top plates and wiring holes. In January it freezes on the nail tips and the underside of the decking as frost. In the first March thaw, all of that melts at once and rains onto the insulation. It looks exactly like a roof leak, shows up on a sunny day, and is spread across the whole attic rather than in one trail. If you see rusty nail tips or a haze of frost on the decking in winter, that's your problem, and the fix is air sealing and ventilation, not shingles.
Bath fan and dryer ducts. A bath fan that ends in the attic — very common in the 1980s houses — dumps a shower's worth of steam into the insulation every morning. Find the duct and follow it. If it stops short of a roof cap or wall cap, or it's a sagging flex duct full of water, that's the leak.
Step 4: the hose test
If the trail doesn't lead anywhere obvious and it's above freezing, have someone in the attic while you run a garden hose on the roof, starting low and working uphill one section at a time, five minutes per section. Don't spray upward under the shingles. When the attic person sees water, the leak is in the section you're wetting. This finds almost everything, and it's the same test we run.
What it costs to fix
| Source | Typical repair |
|---|---|
| Pipe boot | $250–$450 |
| Skylight flashing kit | $400–$900 |
| Valley re-lay with membrane | $500–$1,200 |
| Chimney flashing rebuilt | $600–$1,500 |
| Wall step flashing | $450–$1,100 |
| Bath fan ducted outside | $200–$500 |
| Attic air sealing | $500–$2,000 |
Most of these are one visit. If you've traced a trail and want it fixed, or you've traced it and aren't sure what you're looking at, our roof repair page covers what happens next. Photos from the attic, with the light on the trail, save everyone a trip.
When not to go up
If the ceiling is sagging or bulging with water, poke a small hole in the lowest point with a screwdriver and let it drain into a bucket before it brings the drywall down. If water is coming through a light fixture, turn off that breaker first. And if the roof itself is snow-covered, stay off it entirely — the attic is where the information is in winter anyway.
Need roof work in Maple Grove?
Call for a free estimate. Mon–Sat 7am–7pm.