There are three main places that you should look for leaks in an asphalt-shingle roof: the flashing, the eaves, and the shingles themselves. The materials and skills needed to make repairs will depend on what type of problem you have with your roof.

Flashing Issues

If you have dormers, vent pipes, or a chimney that sticks up from your roof, you will need flashing. The whole purpose of flashing is to guide any water that runs down the vertical surfaces of anything that protrudes from your roof onto the roof itself instead of under the roof. If this flashing begins to pull away from these vertical surfaces, then water can run behind your roof and leak into your house. To repair your flashing, you will need to replace any nails that have begun to pull out with screws, cover the screw heads with roofing cement, and then recaulk the top edge of your flashing to make sure that there is a good seal. 

Eaves and Ice Dams

During the winter, any snow that melts over your roof will allow streams of water to run down your roof. When these streams hit your eaves they can freeze, because the eaves tend to be cooler than other areas of your roof. As layer after layer of ice builds up on your eaves, the ice can create a dam that allows water to run under your shingles and leak into your home. In order to fix this problem, you will need to install a rubberized roof membrane under the shingles on your eaves, so that even if water does run under the shingles it will have nowhere to go. 

Shingle Problems

You can also have problems with your shingles. Hail can punch holes in asphalt shingles, and a strong wind can rip them right off of your roof. If you find hail- or wind-damaged shingles, then you have no choice but to remove and replace them. As long as the damage is not widespread, it will be cheaper to repair the damaged shingles instead of replacing your whole roof. 

If you have a problem with a leaky roof, the damage which causes the roof may not be obvious. You should inspect your shingles and flashing for signs of damage, and during the winter months, you should inspect your eaves for dams. If you have a hard time finding your leak or making the necessary repairs, you can always call in the professionals to give you a hand. A company like Dean Roofing Company can give you more information.