Skylight Installation on Shingle Roofs in Seattle: Flashing, Leak Prevention, and Warranty

Skylights are a natural fit for Seattle homes — when you get 226 cloudy days per year, every ray of natural light counts. But in a city that receives 37 inches of annual rainfall, skylight installation on shingle roofs requires precision flashing and waterproofing that many contractors get wrong.

Skylight Types for Seattle

Fixed Skylights

• Non-opening units that provide light only
• Fewer leak points due to no moving parts
• Best for areas where ventilation isn't needed
• Most affordable option ($300–$800 for the unit)

Venting Skylights

• Open to allow air circulation
• Ideal for kitchens, bathrooms, and lofts
• Manual or electric operation (electric recommended for hard-to-reach locations)
• Higher leak risk due to seals and moving parts ($500–$1,500 for the unit)

Tubular Skylights (Sun Tunnels)

• Small diameter tubes with reflective interior that channel light from the roof to a ceiling diffuser
• Minimal roof penetration — lower leak risk
• Work well in smaller spaces, hallways, and closets
• Most affordable installed ($500–$1,000 complete)

Proper Flashing: The Key to Leak Prevention

In Seattle's wet climate, skylight flashing is the difference between a successful installation and an expensive failure:

Step Flashing

• L-shaped metal pieces woven into each course of shingles along the sides of the skylight
• Each piece overlaps the one below, creating a continuous water barrier
• Must be installed with each shingle course — not added after shingles are in place

Head Flashing (Top)

• Continuous flashing across the top of the skylight
• Must extend under the shingles above the skylight
• Creates a "shingle effect" that channels water around the unit

Sill Flashing (Bottom)

• Flashing at the bottom of the skylight that directs water onto the shingles below
• Must extend over the shingles below — not under them
• The most critical flashing point — this is where most skylight leaks originate

Ice and Water Shield

• Self-adhering waterproof membrane applied to the roof deck around the entire skylight opening
• Required by Washington building code at penetrations
• Extends at least 8 inches beyond the skylight frame on all sides
• Provides backup waterproofing even if flashing fails

Common Installation Mistakes

1. Relying on sealant instead of proper flashing

Caulk and sealant are temporary — they crack, shrink, and fail within 3–7 years in Seattle's UV and moisture conditions. Proper metal flashing is the only reliable long-term solution.

2. Improper step flashing integration

Step flashing must be woven into each shingle course as shingles are installed. Retrofitting step flashing after shingles are in place creates gaps that leak.

3. Insufficient ice and water shield

Skimping on ice and water shield around the opening saves $50 in materials and costs $5,000 in leak repairs.

4. Wrong skylight for the roof pitch

Skylights have minimum pitch requirements. Installing a skylight on a roof below minimum pitch causes water to pool on the glass and seep past seals.

5. Poor curb construction

The curb (the raised frame the skylight sits on) must be built with proper drainage slope and waterproof materials. Poor curb construction is a hidden cause of many skylight leaks.

Warranty Considerations

Manufacturer Warranty

Major skylight manufacturers (Velux, Fakro, Wasco) offer 10–20 year warranties, but coverage varies:

• Glass/unit: Typically 10–20 years against defects
• Seals: 5–10 years against condensation between panes
• Flashing kit: Usually included in the unit warranty if manufacturer flashing is used

Installation Warranty

Your contractor should offer a workmanship warranty of at least 5 years specifically covering the skylight installation. This is separate from the general roof warranty.

Important: Using Manufacturer Flashing Kits

Most skylight manufacturer warranties require use of their specific flashing kit. Using generic flashing — even if properly installed — may void the manufacturer warranty. Always verify warranty requirements before installation.

Cost of Skylight Installation in Seattle

Should You Add Skylights During a Re-Roof?

Yes — this is the ideal time. Adding skylights during a re-roof is significantly cheaper than retrofitting because:

• The roof surface is already open for flashing integration
• Step flashing can be properly woven into new shingle courses
• No existing shingles need to be disturbed
• One permit covers both projects
• Less labor for the combined project

If you're planning a roof replacement and have considered skylights, there's no better time to add them. The incremental cost during a re-roof is 30–50% less than a standalone installation.