WASHINGTON · KING COUNTY / SEATTLE SDCI
Where Puget Sound Storms Meet the Emerald City Skyline
Seattle's wind design is shaped by Pacific winter windstorms rolling in off the Sound, a hilly maritime city, and a seismic backdrop that frequently shares the lateral-load conversation.
CYCLONIC LOWS · SALTWATER FETCH
Reading the Wind Off Elliott Bay and the Hills
Pacific Northwest windstorms arrive as deep low-pressure systems, accelerating across open Sound water before climbing Seattle's ridgelines — exposure, not just speed, drives the pressures.
Winter Windstorm Fetch
Sustained Pacific lows sweep saltwater fetch across Puget Sound, the driver behind the 100–110 mph design gust band.
100–110 MPH · RISK IIHilly Topography
Queen Anne, Capitol Hill and West Seattle ridges can lift Kzt above 1.0 near a crest, returning to 1.0 away from the feature.
Kzt ≥ 1.0 AT CRESTSUrban Exposure B
Dense neighborhoods — Belltown, Ballard, Fremont — shelter into Exposure B, the standard inland category citywide.
Kz 0.85 @ 30 FT (B)Waterfront Exposure C
The Seattle waterfront, Harbor Island and Lake Washington shores open to Exposure C — higher Kz, higher pressures.
Kz 0.98 @ 30 FT (C)Seismic design near the Cascadia Subduction Zone and Seattle Fault often governs the lateral system — yet wind still rules cladding, curtain walls, windows and roofing, so both cases are checked element by element.
SDCI PERMIT CHECKLIST
What a Seattle Permit Set Actually Demands
Six pieces every King County wind-load submittal carries through Seattle Department of Construction and Inspections review.
ASCE 7-22 Per WSBC
Velocity pressures run on ASCE 7-22 as adopted by the Washington State Building Code (IBC base).
ASCE 7-22Washington PE Seal
A Washington-licensed Professional Engineer must seal structural calculations; SE expertise suits complex frames.
WA PE / SECorrect Exposure Call
Justify B inland versus C at the waterfront; in transitional shoreline zones the conservative C is the safe call.
EXPOSURE B / CRisk Category Map
Risk Category sets which speed map you read: II for most buildings, III–IV for assembly, schools and essential facilities.
CAT I–IV MAPSMWFRS + C&C Output
Both main-system and component-and-cladding pressures — windows, panels, roofing — go in the calc package.
MWFRS & C&CSpecial Inspections
SDCI plan review plus special inspection and testing during construction close out WSBC compliance.
SDCI REVIEWB VS C · WHY THE WATERFRONT IS DIFFERENT
The Shoreline Pressure Premium
Same 30 ft, same gust — open Sound exposure simply pulls a larger velocity pressure coefficient than the sheltered urban grid.
| Factor | Inland Seattle (Exp B) | Sound / Lake Front (Exp C) |
|---|---|---|
| Kz at 30 ft | 0.85 | 0.98 |
| Typical neighborhoods | Capitol Hill, Ballard, Fremont | Waterfront, Harbor Island, Lk Washington |
| Surface roughness | Dense buildings & trees | Open water fetch |
| Pressure trend | Baseline | Markedly higher |
Kz values from ASCE 7-22 Table 26.10-1; actual design pressure varies by site, height and the topographic factor at your specific ridge.
CYAN · MAPS & REQUIREMENTS
Keep Mapping the Pacific Northwest
From King County out to the full Washington schedule and neighboring jurisdictions.
Washington Statewide
The full WSBC and ASCE 7-22 picture across the Evergreen State.
STATE GUIDEPortland, OR
Compare the neighboring Cascadia maritime city to the south.
SIBLING CITYAll State Requirements
Every state's adopted code edition and design wind basis.
50-STATE INDEXASCE 7 Standards
How the 7-22 wind provisions feed Washington permit math.
ASCE 7Official references: Seattle SDCI · WA State Building Code Council · WA Board for Professional Engineers.
EMERALD · RUN THE NUMBERS
Calculate Seattle Wind Loads, Site by Site
Enter any King County address — the calculator pulls the 100–110 mph band, resolves Exposure B or C off the shoreline, applies your Risk Category map and returns PE-ready MWFRS and C&C output for SDCI.