Lewis County, WA Building Safety: Building Permits (2026)

020(b) adopts the 2021 International Residential Code with county amendments, and its incorporated permit clause (IRC/IBC/IFC Section 105, UPC Section 104) sets the baseline permit trigger for unincorporated Lewis County. Any owner or authorized agent who intends to construct, enlarge, alter, repair, move, demolish, or change the occupancy of a building or structure, or to erect, install, enlarge, remove, convert, or replace an electrical, gas, mechanical, or plumbing system regulated by the code, must first apply to the Building Official and obtain the required permit before starting work.

in Chehalis, the office named in the code as custodian of the adopted technical codes and the point of application. 2 exempts one-story detached structures used as tool and storage sheds, playhouses, and similar uses, so long as the floor area does not exceed 200 square feet, from needing a permit at all. Above that threshold, or for anything habitable, a permit application is required regardless of the structure's simplicity. 020(2), with the first-named code controlling.