The best way to identify a water leak is to re-create it, no matter if it is a plumbing or roofing leak. Because water travels with gravity, identifying the true source of a leak takes some time and investigation. The majority of roofing leaks are caused from areas where the intersecting roofing systems and surfaces meet, such as chimneys, stack pipes, skylights and additional stories.
To ensure the water is coming from this area, wait until the next rainfall or get your garden hose and heavily water down the area. Research the attic to verify the water’s entry point, keeping in mind water will travel downhill. Meticulously follow the water to identify the source of entry. Once identified, you have won half the battle.
The intersection of a garage and the second story of a house is a common cause for deteriorating flashing and/or sealant. The flashing is typically a long-lasting membrane or metal, such as copper or aluminum, that is installed underneath the shingles and upside the vertical surface. It is used to divert the water off the roof. After identifying the cause of the leak, it’s time to repair it.
And lastly, remember to be extra cautious when doing anything on the roof. If you're not comfortable being up on a roof, hire a professional to repair the leak.