The source of most roof leaks is hard to find because it originates away from where the leak shows up. In order to find the source of a leak, follow a roofer’s advice and “think like water.”
Water typically comes in through worn, broken, or missing shingles; where nails have worked loose; or through corroded or poorly sealed roof flashing around vents, skylights, or chimneys or along the intersections of roof planes.
How to find a roof leak
A roof leak often travels down a rafter, showing up down-roof from where it begins. Once water passes the roofing, it flows along the sheathing, roof rafters, or topside of ceilings until it finds a place to drip down—inevitably onto your favorite piece of furniture.
Visual inspection for leaks
It is best to look for a roof leak during the day by way of visual inspection. Find your way into the attic (ceiling) with a flashlight, starting above the place where the drip has occurred and work your way uproof, looking for wetness along the framing.
If the weather has been dry for a while, look for water marks, stains, or discolorations on the wood made by moisture. Then switch off the light and try to find a hole where daylight shows through the roof. If it’s still raining, put a bucket under the leak in an area with proper support.
Water-testing for leaks
If you can’t find the cause of a leak by visual inspection on the roof surface, wait for dry weather and ask a friend to help you do a water test. To do this, one person goes onto the roof with a hose; the other person goes inside the ceiling with a bucket and a strong light.
The person in the ceiling watches carefully while the one on the roof floods the roof with the hose, starting at the bottom (the eaves) and slowly working uproof until water from the leak appears in the ceiling. Once the leak is found, push a nail up through the hole to mark its location for rooftop repair. Mark the surface of the roof with chalk, if necessary.
Repairing the roof leak
The exact methods for repairing the roof leak will depend upon the roofing material and the roof’s construction. But if you know that a roof leak is being caused by a hole, a quick fix can be done with a piece of galvanized sheet metal flashing, available at most hardware stores.