Locating a roof leak can be challenging, because often a roof will leak in one place and the water will flow to another before it starts to show on the ceiling. While you might assume that the roof is leaking directly above a water spot on your ceiling, this may not necessarily be true. This is because water tends to flow in the path of least resistance. It's possible that the water is showing several feet below where the roof is actually leaking. Here's how to spot "invisible" leaks in your roof easily, so you can repair the roof or have it replaced.
Visit Your Attic on a Rainy Day
By far the easiest way to determine the location of a roof leak is to head up to your attic with a flashlight on a rainy day. Scour the entire area of the roof with your flashlight, and mark any wet spots that you see. Once the weather dries up, get someone to help you locate the spot on the outside of the roof by having them tap on the area while they're inside. You can then put new shingles on that area or seal the area with roofing cement.
If you'd rather find the leak now, even if it isn't raining, you can use your garden hose to mimic rain on your roof. The same concept applies: simply look for the wet spots on the underside of the roof in the attic. Slower leaks may take longer to show up with this method, so if you don't notice any wet spots soon after turning the garden hose on, be patient. The water spots will likely show up over time.
What If You Don't Have an Attic?
If you don't have an attic, there are still several ways you can check for water damage to your roof. Check the ridge caps and the flashing round your chimney if you have one. Also, check your dormer valleys, the gaskets around pipes, around your gutters and downspouts, and the shingles themselves. When inspecting shingles, look for shingles that are lifted or raised, or shingles that have cracks or holes in them. Flashing should be inspected for discoloration, corrosion, or looseness. These areas can be fitted with new shingles or roofing cement if they are showing water damage.
You'll also want to inspect your roof for any exposed roofing nails that could be the source of your leak, or for gutters and downspouts that are clogged and causing water to back up around the flashing. Work from one side of the roof to the other, and always remember to use proper safety equipment, including a sturdy ladder and a safety harness.
What to Do If You Can't Find the Leak
In some cases, you may not be able to find the leak that is causing water spots to show up on your ceiling, despite your best efforts to locate it. Contacting a professional that specializes in roof repairs and roof replacement can help you quickly locate the leak. A skilled roofing contractor may be able to repair the roof in the area of the leak, or locate and repair multiple leaks if they are present. However, if your roof is over 20 years old, you may need to have a roof replacement done.
Depending on the material used in your roofing, you could need your roof replaced every 20 to 50 years, or in cases where there is significant damage to the roof that would be costlier to repair than to do an entire roof replacement. A roofing professional can thoroughly evaluate your roof and determine what the best course of action would be in your particular situation.