Roof leaks can occur without any type of shingle damage. These types of leaks occur when water somehow makes its way beneath the shingles, most often by backflowing underneath the lower edge. Watch out for these common causes of under-shingle leaks so you can fix them before a problem occurs.
1. Roof Moss
Moss is most often a problem on shaded roofs and on the north side of roofs in damp climates. Moss traps moisture against shingles, which can cause shingle decay and leaks over time. In the short term, under-shingle leaks can occur from a dam effect. Rain runoff down the roof will hit a moss clump, causing the water to backflow under the shingles behind the moss.
Roof cleaning can get rid of existing moss. To prevent future moss growth, ask your roofing company to install zinc strips near the upper rows of shingles. Zinc will leach out and coat the roof with an invisible barrier that prevents moss growth.
The upslope edge of a skylight acts very much like the moss as it also creates a dam effect and backflow leaks. Further, the water that pools up against the skylight will also eventually break the seals and leak. Skylights aren't the only rooftop installation to have this problem. Vents, satellite dishes, and other rooftop penetrations can also create dams.
Fortunately, there is a solution. A roofer can install wedge-shaped shuttles upslope from the skylight. The shuttles are angled so water flowing toward the skylight is shunted around it. Properly placed shuttles will eliminate both backflow and seal leaks.
3. Clogged Gutters
Dirty gutters don't just overflow below, some of that blocked water also flows up and under the shingles. In winter, this backflow can freeze beneath the shingle and create a large ice dam that will eventually melt and leak into your home. Debris from overhanging trees and blown-in leaves are the usual cause of clogged gutters.
The simplest solution is to prevent problems in the first place by cleaning out the gutters regularly. Trimming back trees so less debris falls on the roof and gutter will also help. If there is concern that damage may still occur, then have your roofers install both a drip edge and an ice and water barrier beneath the standard moisture barrier to provide additional protection. This is best done at the time of roof replacement.
Contact a roofing contractor if you have concerns that one or more of these problems are present on your roof.