General Exterior Code Requirements in Washington

Growth Management Act (GMA) requires protection of critical areas: wetlands, fish & wildlife habitat conservation areas, frequently flooded areas, geologically hazardous areas, critical aquifer recharge areas. Local CAOs (Critical Areas Ordinances) apply.

Mount Rainier lahars (volcanic mudflows) pose risk to Pierce, King, Lewis counties along Puyallup, Carbon, White, Nisqually, and Cowlitz river valleys. Tacoma, Puyallup, Orting, Auburn at risk. USGS hazard maps.

Mount St. Helens (active, last eruption 2004-2008) poses lahar and ashfall risk to Cowlitz, Skamania, Lewis counties. Toutle River drainage. Castle Rock, Longview, Kelso at risk.

Extensive flood hazard areas including Puget Sound river valleys, Columbia River, eastern WA rivers. Skagit, Snoqualmie, Chehalis, Yakima rivers have significant flood history. FEMA FIRM maps.

Significant landslide risk in western WA steep slopes, Puget Sound bluffs, river valley walls. 2014 Oso landslide (43 deaths). DNR landslide hazard maps. Geotechnical investigation required.

Cascade Range passes and eastern WA mountains have extreme snow loads (50-300+ psf ground snow load). Snoqualmie Pass, Stevens Pass, White Pass, Leavenworth, Chelan. Site-specific snow load analysis often required.

Ice barrier required throughout Washington per WSRC R905.2.7.1. Applies to asphalt shingles, metal, clay/concrete tile. Extends from eave edge to 24 inches inside exterior wall line.

Shoreline Management Act (SMA) regulates development within 200 feet of shorelines of statewide significance. Includes marine waters, major rivers, lakes >20 acres. Substantial Development Permit (SDP) required.

Numerous National Register historic districts throughout WA. Major districts in Seattle (Pioneer Square, Pike Place), Tacoma, Spokane, Port Townsend, Bellingham, Olympia. Local historic preservation requirements.

Entire western Washington is SDC D or higher due to Cascadia Subduction Zone. Risk of M9.0+ megathrust earthquake. Seattle Fault directly under downtown. Liquefaction risk in fill and river delta areas.

Areas with soil conditions susceptible to liquefaction during seismic events. Geotechnical investigation required per ASCE 7-22 Section 11.8.2.

Significant WUI areas throughout eastern Washington, eastern slopes of Cascades, and pockets in western WA. DNR maps wildfire risk. Local jurisdictions may adopt IWUIC or local WUI standards.

Pacific coastal areas (Grays Harbor, Pacific, Clallam, Jefferson counties) face tsunami risk from Cascadia event. Inundation maps published by DNR. Vertical evacuation structures may be required for critical facilities.