The 2015 International Building Codes became effective in Washington State on July 1, 2016. This code family consists of the International Building Code (IBC), the International Residential Code (IRC), the International Mechanical Code (IMC), the International Fire Code (IFC) and 2015 Washington State Energy Code.
The International Building Codes, without state or county amendments, are available at IBC site
The Washington State Building Code Council also has information about the adoption of codes and the Washington State Amendments (external link).
King County's amendments to the codes are contained in Title 16 (PDF*, 398KB) and Title 17 (PDF*, 72KB) of the King County Code, online at www.kingcounty.gov/council/legislation/kc_code.aspx.
The climatic and geographic design criteria for King County are available online in Table R301.2(1) (PDF*, 92KB) of the International Residential Code.
The Permitting Department Customer Information Bulletin #27, (currently being updated.) Residential Energy Codes, provides detailed information.
Customers also can call the Permitting Department at 206-296-6600 and ask to speak with a plans examination engineer.
King County determines snow loads via the Structural Engineers of Washington study. If you know the approximate general area of the County in which your site is located, you can access the snow load map at: kingcounty.gov/depts/permitting-environmental-review/gis/ReferenceMaps. Simply click on the King County Ground Snow Load map section you are interested in.
As you zoom into your site, determine the appropriate isobar and calculate the ground snow load by using the following equation: ground elevation above sea level in feet multiplied by the isobar line number equals ground snow load in pounds per square foot.
Example: A site in Maple Valley section 14, T22N, R6E at 700 ft elevation. From the snow load map, the isobar line is determined to be .052. The ground snow load would be 36 psf [700 ft x .052 = 36 psf].