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�MyBui ldi ngPermit xom <br />a service of eCityGov.net Construction Tip Sheet 01 <br />Basic Stairs <br />This tip sheet reflects code requirements of the 2018 International Residential Code (IRC) with <br />Washington State Amendments. <br />36" min. to near <br />obstruction <br />N � X <br />N CM M <br />h E <br />Nosing <br />3/4" -1 1 /4" <br />-r.--.4 <br />Figure 1: Typical Stair Treads and Risers <br />Stair Treads and Risers <br />Nosing required at solid <br />riser <br />At open risers, a sphere <br />4" in diameter cannot <br />pass through (except for <br />stairs with a total rise of <br />30" or less). <br />Protect enclosed <br />accessible space under <br />stairs with 1/2" gypsum <br />board. <br />❑ The largest tread or riser within any flight of stairs is not to exceed the smallest by more than <br />3/8 inches. (R311.7.5) <br />Illumination <br />❑ Interior stairways shall be provided with an artificial light source to illuminate landings and <br />treads. There shall be a wall switch at each floor level to control the light source where the <br />stairway has 6 or more risers. (R303.7) <br />❑ Exterior stairways shall be provided with an artificial light source located at the top landing of <br />the stairway and located at the bottom landing where accessing a basement. (R303.8) <br />Handrails <br />❑ Handrails are required on at least one side for stairways with four or more risers. See Tip Sheet <br />2 for additional information regarding handrails. (R311.7.8) <br />January 22, 2021 MyBuildingPermit.com I Basic Stairs 1 <br />eC yGov.net <br />2005 k. echcoyNhance <br />sic) <br />