Window Climate Specs for Seattle, WA
ENERGY STAR groups King County into its Northern zone, which is the U-factor and SHGC target worth checking against any quote you get in Seattle. The longest-licensed window contractors based in Seattle are listed below the climate data.
Licenses checked · Washington State Department of Labor & Industries
4CIECC climate zone · ENERGY STAR Northern zone
Seattle's climate zone, in plain terms
Seattle-Tacoma-Bellevue, WA runs a January average near 42°F and climbs to about 67°F by July, a swing that adds up to roughly 4,483 heating degree days most winters, with 211 on the summer cooling side of the ledger.
That load is the actual argument for paying up for a better U-factor in Seattle, separate from anything a brochure claims.
Zone 4C's requirement is the floor; Seattle's specific load is what tells you whether beating that floor is worth the extra cost.
Data: U.S. EPA / DOE, ENERGY STAR, ENERGY STAR Version 7.0 Climate Zones by County/ZIP (Windows, Doors, and Skylights) (V7.0); Pacific Northwest National Laboratory (DOE Building America), Guide to Determining Climate Zone by County: Building America and IECC 2021 Updates (PNNL-33270) (2021 IECC), from the nearest NOAA station 6.5 mi away.
What FEMA's risk data says about Seattle
FEMA scores King County's winter-weather risk as Relatively High and its flood risk as Very High.
Winter risk in Seattle weighs on U-factor and condensation resistance; flood risk weighs more on sill height and drainage detailing than on the glass package.
Treat these as two separate conversations with a Seattle contractor, not one.
- Strong wind
- Very Low
- Winter weather
- Relatively High
Data: FEMA, National Risk Index for Natural Hazards - County-level table, v1.20 (v1.20, December 2025).
Guides to finish before Seattle window bids come in
- How to Read an NFRC Window Label Four numbers on one sticker decide most of a window's real-world performance. Here's what each one means.
- ENERGY STAR Window Criteria by Climate Zone ENERGY STAR splits the country into four zones, each with its own numbers. Here they are, and why the Northern zone works backward from the other three.
- Impact Windows vs. Shutters in Florida's Hurricane Zones Florida gives homeowners two paths to a protected opening. Here's how each one is tested, and where the HVHZ raises the bar further.
Seattle's longest-licensed window installers
Oldest license first, newest last, pulled directly from the state's file. This list isn't for sale.
- Windorco Supply INCVerify license
- Seattle Glass INCVerify license
- R E Glaze Unlimited INCVerify license
- Wakefield Glass INCVerify license
- Cherry CRK Door/Window CO INCVerify license
- Double Hung Window RestorationVerify license
- Glass Scratch RemoversVerify license
- Cascade Glass COVerify license
- Pacific NW Siding/Windows INCVerify license
- Windows Doors & More INCVerify license
- Northwest Shower DoorVerify license
- Unique Art Glass LLCVerify license