How Does a Roof Leak Start?

Weather
1. Surprisingly, the sun does more to damage a roof than wind or rain. The constant bombardment of the sun’s rays works to make shingles brittle over time. The sun also softens the tar that binds shingles together, which makes them susceptible to warping. Due to warping and cracking, rainwater can penetrate through the interlocking system of shingles your roof integrity depends on.

Rain and wind, after the sun, are the most common causes of roof leaks. Stormy weather can make shingles shift, bypass imperfect seals around vents and flashing, and otherwise infiltrate beneath the shingles and roofing felt.

Lack of Workmanship and Roof Abuse
2. If a roof is not put on properly in the first place, it is susceptible to immediate leakage. You won’t have to wait long after getting a new roof to discover whether your contractors did their job. The first heavy rainstorm will be your litmus test.

The most common origination of a roof leak due to poor workmanship is valleys, those sloping canals that occur between two sections of pitched roof. Valleys must be tar papered in the herringbone style, as must the shingles, and between those layers should be a single piece of metal flashing running all down the length of the valley. If this part is not done properly–which happens from time to time in the roofing industry, which tends to hire laborers when it should be employing skilled professionals–your roof will leak. If you pay for real roofers you’ll likely avoid that. (The second most common place for a roof leak to start is all along the ridges, not because of a lack of workmanship, but because ridge caps are susceptible to sun and wind damage.)

Roof abuse happens when homeowners walk on hot shingles with, say, cleated combat boots. The heat melts the tar, making the shingles temporarily impressionable, and the rough-bottomed shoes wreak their permanent havoc. Skidding down a roof or putting undue pressure on shingles is another big Don’t.

Lack of Maintenance and Inspection
3. Loose shingles, vents or flashing can allow water to seep underneath–even uphill, against the pitch of the roof–due to wind. Worn-down shingles due to weather or abuse tend to cause leaks as well. Most roof leaks can be avoided with twice-annual inspection.

Note that most roof leaks start with age, as all roofs need eventual replacement. [ehow]