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PART 300 Amendments to the International Residential Code.
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IRC Table R 301.2(1) is amended to read:

Table R301.2(1) Climatic and Geographic Design Criteria

Minimum Roof Snow Load

Wind Design

Seismic Design Category

Subject to Damage From

Winter Design Temp

Ice Barrier Underlayment Required

Flood Hazards

Air Freezing Index

Mean Annual Temp

Speed

Topographic Effects

Special wind region

Windborne debris zone

Weathering

Frost line depth

Termite

25 psf

May increase. See footnote a.

For prescriptive structural design under IRC, 110 mph shall be used.

See IBC Wind Maps for structural design under IBC.

See footnote b.

See footnote c.

NO

NO

D2/D

See footnote d.

Moderate-Severe

See footnote e.

18 inches

Moderate

26° F

NO

12/23/71

(See footnote f(1).

6/19/20

See footnotes f(2) and f(3).

175

50.5° F

aThe roof snow load may be greater than 25 psf depending on site location. Verify the ground snow load with a Plans Examiner prior to design. The ground snow load will vary according to site and shall be applied as the roof snow load when prescriptive structural design under the IRC is used for design. The roof snow load may be reduced by a Washington State licensed design professional with a structural analysis as allowable in the IBC. The roof snow load used in design is not permitted to be less than 25 psf.

bA wind speed of 110 mph shall be used for prescriptive structural design based on the IRC. If the structural design is in accordance with the IBC, the applicable wind map under the currently adopted and implemented IBC shall be used for design. The wind exposure category shall be determined on a site-specific basis either by the designer under the IRC prescriptive structural design or by the Washington State licensed design professional under the IBC.

cTopographic effects shall be included for buildings structurally designed in accordance with the IBC.

dSeismic Design Category D2 shall be used for prescriptive structural design based on the IRC. If the structural design is in accordance with the IBC, Seismic Design Category D shall be used. The Washington State licensed design professional is responsible for determining if a higher seismic design category is applicable at the site.

eSee Weathering Probability Map for Concrete in IRC for site specific weathering.

f(1) 12/23/71 is the date of the county’s entry into the National Flood Insurance Program, (2) 6/19/20 is the date of the county’s currently effective Flood Insurance Study, and (3) 6/19/20 is the date of the county’s currently effective Flood Insurance Rate Map, as may be amended.

(Added by Amended Ord. 07-084, Sept. 5, 2007, Eff date Sept. 21, 2007; Amended by Amended Ord. 11-031, Aug. 3, 2011, Eff date Aug. 18, 2011; Amended by Amended Ord. 14-057, Aug. 27, 2014, Eff date Sept. 13, 2014; Amended by Ord. 17-057, Oct. 18, 2017, Eff date Nov. 9, 2017; Amended by Ord. 21-030, July 14, 2021, Eff date July 25, 2021).