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WA Residential Code 2018 <br /> R408.3 Unvented Crawl Space <br /> Ventilation openings in under-floor spaces specified in Sections R408.1 and R408.2 shall not be required where: <br /> 1.Exposed earth is covered with a continuous Class I vapor retarder.Joints of the vapor retarder shall overlap by 6 inches(152 <br /> mm)and shall be sealed or taped.The edges of the vapor retarder shall extend at least 6 inches(152 mm)up the stem wall and <br /> a radon system shall be installed that meets the requirements of Appendix F(Radon)of this code. <br /> 2.Continuously operated mechanical exhaust ventilation is provided at a rate equal to 1 cubic foot per minute(0.47 L/s)for each <br /> 50 square feet(4.7 m2)of crawlspace floor area.Exhaust ventilation shall terminate to the exterior. <br /> Exception:Plenum in existing structures complying with Section M1601.5,if under-floor space is used as a plenum. <br /> Exported by Q UpCodes https://up.codes <br />