Your roof can appear to be in perfect condition, yet water may still be making its way beneath the shingles and leaking into your home. There are several reasons why water can seep beneath shingles and cause leaks.
1. Clogged Gutters
One of the most common reasons water washes underneath a shingle is a simple clogged gutter. When a gutter or downspout is blocked with debris, the trough can't take on any more of the runoff water at the roof. This causes the water to momentarily backflow up the roof before simply washing over the gutter trough. During this moment of backflow, water will go beneath the shingles. When this happens repeatedly, the wood sheathing beneath the shingles becomes saturated and water begins to leak inside your home.
2. Moss Growth
Moss only grows on the surface of your roof, so it doesn't penetrate or form holes in the shingles. However, it can creep its way beneath the shingles around the edges, which will slowly lift the shingle so it doesn't lie flush against the sheathing anymore. This allows water under the shingle, so eventually a leak will form as the sheathing becomes saturated or begins to suffer from water rot. Moss also traps moisture, which can make the leaking more severe.
3. Debris Buildup
Piles of leaves and fallen twigs are the main types of debris you can find on a roof. Debris can hide damage, but even without damage, water can get beneath the shingles. Debris acts like a dam, trapping water as it runs off the roof and causing it to flow back up and beneath the shingles. Even if the trapped water doesn't get under the shingles right away, the constant moisture exposure from pooling water can degrade shingles enough for water to seep beneath.
4. Tree Branches
When a tree branch scrapes against a roof, it can ruffle up the shingles. The waterproof membrane provided by shingles is then compromised once the shingles are no longer lying flat. Plus, those shingles are more likely to crack and develop permanent leaks. Trimming back branches so they don't scrape against the shingles is a must if you don't want water to get beneath them.
Walking on the roof can cause all sorts of little problems that allow water beneath the shingles. Shingles can become cracked, the edges might chip, or the water-resistant gravel coatings can be dislodged. It's best to stay off your roof to avoid these types of damage. Never install things on the roof without a professional, either, as one wayward nail can lead to a big leak.
Contact a roof repair service if you suspect water has made its way beneath your shingles.