How do you find where a roof is leaking?
Short answer. To find where a roof is leaking, go into the attic during or right after rain with a flashlight and trace the wet trail uphill along the rafters and deck to its highest point, then check the roof above that spot for the usual suspects: pipe boots, flashing, vents, valleys and nail pops. If it is not raining, a controlled hose test, starting low and working up with someone watching inside, pinpoints the spot.
Step 1: Use the attic
- Bring a strong flashlight and step only on joists or boards.
- Look for wet wood, dark stains, water trails on rafters, rusty nail tips and wet insulation.
- Follow the trail uphill. Water runs along rafters and the underside of the deck, so the entry point is often several feet from the ceiling stain.
- Look for daylight at penetrations, though not every leak shows light.
Step 2: Match it to the roof
Measure from a gable wall or a vent pipe in the attic and find the same spot outside. Then look for:
- Cracked pipe boot collars.
- Step flashing along walls and dormers, and the kick-out at the bottom.
- Chimney flashing, crown or cap.
- Valleys clogged with debris.
- Exposed or popped nails, and missing or lifted shingles.
- Box vents, ridge vents and skylights.
Step 3: Hose test if needed
- With someone in the attic, run a garden hose gently on the lowest suspect area for 10 to 15 minutes.
- Move up the roof one area at a time.
- When water appears inside, you have found it.
Never spray up under shingles, which forces water where rain would not go.
Rule out look-alikes
Condensation in a poorly vented attic, a leaking bath fan duct, HVAC condensate lines and plumbing can all mimic roof leaks. Drips only on cold mornings point to condensation. See common causes of roof leaks and pipe boot leaks.