Why Dormers Are a Common Roof Leak Source in Seattle Homes

In neighborhoods across Seattle and the greater Puget Sound region, dormers are everywhere. From classic Craftsman homes to mid-century additions, dormers add charm, usable space, and natural light. But from a roofing perspective, they also introduce one of the most common—and most misunderstood—sources of leaks.

Dormer intersections are detail-heavy, and in Seattle’s long, wet seasons—especially during heavy spring rain—small flaws can turn into persistent water intrusion.

A dormer is a structural interruption in your roof plane. Anytime a roof meets a vertical wall, you create multiple transition points where water has to be carefully directed and controlled. In a simple roof, water sheds downward with minimal obstruction. With dormers, however, you introduce:

• Sidewall-to-roof intersections
• Valleys or mini-valleys above the dormer
• Siding-to-roof transitions
• Multiple flashing layers working together

Each of these areas must be installed perfectly to keep water out. And in Seattle, where roofs are exposed to months of steady moisture, even minor imperfections get tested over time.

Step flashing is installed where the sloped roof meets the dormer wall. It’s designed to “step” up the wall with each shingle course, directing water back onto the roof surface instead of behind the siding. When done correctly, it’s extremely effective.

But in many Seattle homes, step flashing issues are common:

• Improper overlap between pieces
• Nails placed too high or exposed
• Flashing reused during a roof overlay or replacement
• Missing integration with underlayment or house wrap

These issues don’t always leak right away. In fact, a dormer can perform “fine” for years until cumulative exposure, debris buildup, or heavier-than-normal rain overwhelms the system.

At the bottom of a roof-to-wall flashing section, where the roof slope ends at the gutter, there should be a critical piece called kickout flashing. Its job is simple: redirect water away from the wall and into the gutter.

Without properly installed kickout flashing, water runs down the sidewall and can slip behind the siding. Over time, this leads to:

• Rotting sheathing
• Interior wall leaks
• Mold or mildew issues
• Hidden structural damage

Many older Seattle homes either don’t have kickout flashing at all or have undersized versions that can’t handle heavy rain flow. This is one of the most common “invisible” causes of dormer-related leaks.

Another overlooked issue is siding clearance. Ideally, siding should be installed slightly above the roof surface to prevent constant water contact and allow proper drainage. In practice, siding is often installed too low—sometimes even touching the shingles.

This creates a few problems:

• Water wicks up behind the siding
• Flashing becomes less effective
• Debris and moss get trapped at the intersection
• Drying is slowed dramatically in damp conditions

In Seattle’s climate, where roofs stay wet for long periods, these conditions accelerate deterioration and eventually lead to leaks that appear to come “out of nowhere.”

One of the most frustrating aspects for homeowners is timing. The dormer didn’t leak for 5, 10, even 15 years, so what changed? The answer is usually a combination of slow degradation and environmental stress:

• Sealants dry out and crack
• Flashing shifts slightly over time
• Moss and debris alter water flow paths
• Heavy spring rains overwhelm marginal details

Long periods of steady rain allow water to find and exploit even the smallest weaknesses. What used to shed properly may now back up, seep sideways, or penetrate behind flashing layers.

Dormer leaks aren’t typically solved with surface fixes like caulking or patching. Those approaches may stop water temporarily, but they don’t address the underlying problem. A proper repair involves:

• Removing shingles and siding as needed to expose the intersection
• Inspecting and replacing damaged sheathing
• Installing new step flashing correctly layered with underlayment
• Adding or upgrading kickout flashing
• Ensuring proper siding clearance
• Rebuilding the system so water is directed, not just blocked

This detail-forward approach is what separates a short-term fix from a long-term solution.

At Chet’s Roofing & Construction, we specialize in diagnosing and repairing complex roof leak sources, including dormers and other high-risk transitions. Our team takes a detail-oriented approach to ensure the problem is fixed at its source, not just covered up.

Call (877) 611-1514 today to schedule your inspection or request a free estimate. Let us help protect your home with repairs built to handle Seattle’s toughest weather.