Water Damage Behind Asphalt Shingles: What Happens

Asphalt shingles are designed to shed water, but they are not waterproof. Over time, wind, rain, and temperature swings can lift the edges or create small cracks. When water finds a gap, it can slip underneath and run down the roof deck, often traveling far from the original entry point.

The water then soaks into the plywood or OSB sheathing, the underlayment, and the rafters. If the roof has a low slope or a complex valley, water can pool and work its way into the attic or wall cavities. This is why damage often shows up far from the actual leak.

If left alone, the trapped moisture causes rot in the wood structure. Plywood can delaminate, rafters can weaken, and insulation loses its R-value. Mold can start growing within a couple of days, especially in warm, dark spaces like an attic.

Eventually, the damage can spread to interior ceilings and walls. Drywall becomes stained and saggy, and paint blisters. The roof itself may sag or develop more leaks. Catching it early saves you from a bigger repair job down the road.

If the leak is small and you catch it early, you might be able to fix the shingle yourself by applying roofing cement or replacing a single tab. But if water has soaked into the sheathing or spread to the interior, professional help is wise. The pros can open up walls, dry the structure, and repair the roof deck properly.

They can also check for mold, which may require a mold professional if it is widespread. If you live in Kirkland, keep a list of local roofers and the pros handy. Acting quickly can prevent the damage from turning into a much larger and costlier repair.