How a Dormer Is Built
A dormer is a framed box that breaks through the main roof plane. It has its own walls (called cheeks), a face that usually holds a window, and a small roof of its own. Common styles include the gable dormer (with a peaked roof), the shed dormer (a single flat-sloped roof, popular for adding wide spans of upstairs space), and the hipped dormer (sloped on three sides).
Because a dormer interrupts the clean run of the main roof, it creates extra valleys, sidewall joints, and transitions where two roof surfaces meet. Each of those junctions has to be flashed and sealed correctly, which is why dormers are one of the most detail-heavy parts of any roof.
Why Dormers Matter in the Spokane and Inland Northwest Climate
Dormers create the exact conditions our climate punishes hardest. Where a dormer wall meets the main roof, a valley forms that funnels snowmelt and rain into a narrow channel. In Colbert, Spokane, and across North Idaho, those valleys carry heavy snow loads and are prime spots for ice dams to build up during freeze-thaw cycles.
- Ice dams: Heat escaping the dormer can melt snow that refreezes at the colder eave, backing water up under the shingles around the dormer base.
- Sidewall leaks: The joints where dormer cheeks meet the roof rely entirely on step flashing and kick-out flashing to stay watertight.
- Wind and hail: A dormer's vertical face and small roof are exposed surfaces that take extra punishment from driving wind and hail.
Flashing and Maintenance: The Make-or-Break Details
A dormer that leaks almost never fails because of the shingles themselves. It fails at the flashing. Step flashing interlocks with each course of shingles along the dormer's sidewalls, and a kick-out flashing at the bottom diverts water away from the wall instead of behind the siding. Skipping or sloppily installing either one is a leading cause of hidden water damage and rot.
For Inland Northwest homes, we also recommend ice-and-water shield membrane in the dormer valleys and along the eaves to guard against ice-dam backup. If you have older or worn dormers, a full roof replacement is the right time to correct undersized flashing and protect those vulnerable junctions for the long term.
Signs Your Dormer Needs Attention
Watch for these warning signs around a dormer, especially after a hard winter:
- Water stains or peeling paint on interior walls or ceilings near the dormer
- Rusted, lifted, or missing flashing where the dormer meets the roof
- Shingle granule loss, cracking, or curling in the dormer valleys
- Soft or discolored siding at the base of the dormer (a sign of a missing kick-out)
- Ice buildup that returns to the same spot every winter
Catching these early prevents framing rot and interior damage. If you spot any of them, a free estimate from a GAF Master Elite contractor will tell you whether it is a simple flashing repair or something more.