Washington climate zones
Washington’s 39 counties fall in 4 IECC 2021 climate zones: 4C (14), 5B (18), 5C (4), 6B (3).
Zone 4C: mixed-marine
Attic target R60 (ENERGY STAR)Clark County (Marine) · Cowlitz County (Marine) · Grays Harbor County (Marine) · Jefferson County (Marine) · King County (Marine) · Lewis County (Marine) · Mason County (Marine) · Pacific County (Marine) · Pierce County (Marine) · Skagit County (Marine) · Snohomish County (Marine) · Thurston County (Marine) · Wahkiakum County (Marine) · Whatcom County (Marine)
Zone 5B: cool-dry
Attic target R60 (ENERGY STAR)Adams County (Cold) · Asotin County (Cold) · Benton County (Cold) · Chelan County (Cold) · Columbia County (Cold) · Douglas County (Cold) · Franklin County (Cold) · Garfield County (Cold) · Grant County (Cold) · Kittitas County (Cold) · Klickitat County (Cold) · Lincoln County (Cold) · Okanogan County (Cold) · Skamania County (Cold) · Spokane County (Cold) · Walla Walla County (Cold) · Whitman County (Cold) · Yakima County (Cold)
No zone on file
Clallam County (Marine) · Island County (Marine) · Kitsap County (Marine) · San Juan County (Cold)
Zone 6B: cold-dry
Attic target R60 (ENERGY STAR)Ferry County (Cold) · Pend Oreille County (Cold) · Stevens County (Cold)