Design Criteria

Cowlitz County Design Criteria 

The Washington State Building Code includes the 2015 International Building Code (IBC) and International Residential Code (IRC) as adopted pursuant to the Cowlitz County Code (CCC) Title 16. The following design criteria are applicable within the jurisdiction of Cowlitz County.

WIND LOADS:

Commercial structures, IBC Section 1609 –

  • Ultimate Design Wind Speed Vult: Figures 1609.3(1), 1609.3(2) and 1609.3(3).
  • Exposure Category shall be established by the designer in accordance with Section 1609 or ASCE 07.

Residential structures, IRC Section R301.2.1 –

  • Ultimate Design Wind Speed Vult: 110. IRC Figure R301.2(4)A.
  • Exposure Category shall be established by the designer in accordance with Section R301.2.1.4.

EARTHQUAKE LOADS:

Commercial structures, IBC Section 1613 –

  • Seismic Design Category D. Site specific information may be obtained from the U.S. Seismic Design Maps developed by the United States Geologic Survey.

Residential structures, IRC Section R301.2.2 –

  • Seismic Design Category D1.

SNOW LOAD:

Ground snow load, Pg: Refer to CCC Section 16.05.070 Table A.

 FROST DEPTH: 12 inches

CLIMATE:

  • Winter Design Temperature: 22 F degrees.
  • Mean annual temperature: 51.5 F degrees.
  • Air Freezing Index: 170

FLOOD HAZARD:

Flood Hazard construction shall comply with the provisions of CCC 16.25 "Flood Management".

SOIL:

Commercial structures, IBC Section 1803 -

Residential structures, IRC Sec R401.4 –

Unless determined otherwise by soil investigation, presumptive load-bearing value 1500 PSF.