How to Find Where a Roof Leak Is Really Coming From

Why the drip is rarely under the hole

Water that gets past the shingles almost never falls straight down. It runs along the underside of the roof decking, follows rafters and trusses, and soaks into insulation until it finds a low point. That low point might be a ceiling light, a drywall seam or the top of a wall several feet away from where the water actually got in. That's why patching the shingles directly above a stain so often fails.

The most common leak points

Most roof leaks start at a joint or a penetration rather than in the middle of a field of shingles:

• Plumbing vent pipes. Rubber pipe boots crack in the sun and let water run down the pipe. See pipe boot flashing.
• Chimneys. Failed step, counter or cricket flashing. See chimney flashing systems.
• Roof-to-wall joints at dormers, second stories and additions. See step vs continuous flashing.
• Valleys, where two roof planes meet and carry the most water.
• Skylights, usually at the flashing rather than the glass.
• Exposed or backed-out nails and lifted shingles from wind.
• Roof edges without drip edge or kick-out flashing.

What you can check safely from inside

Stay off the roof. From inside you can still gather useful clues: note where the stain is, whether it appears only during wind-driven rain or every rain, and whether it shows up after heavy rain or days later. If you can safely reach the attic, look with a flashlight during or just after rain for wet decking, dark streaks on rafters, rusty nail tips or compressed, damp insulation. Follow wet wood uphill — the entry point is usually above and toward the ridge from the stain. Take photos and note the date.

How a contractor traces it

A proper leak search looks at the roof and the attic together. We inspect every penetration and flashing detail above the wet area, check shingles for lifted tabs and broken seals, and follow the water path inside. If the source is still unclear, a controlled water test — wetting one section at a time from the bottom up while someone watches inside — isolates it.

When it isn't the roof

Not every ceiling stain is a roof leak. HVAC condensate lines, bathroom fan ducts, plumbing and winter attic condensation all leave similar marks. See ceiling stain causes.

If you're chasing a leak that keeps coming back, our roof repair team traces it to the source and repairs the decking and interior damage it caused.

Frequently Asked Questions

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