This bill adds a new section to chapter 36.70A RCW requiring any city or county that plans under RCW 36.70A.040 to allow at least one mobile dwelling unit on each lot zoned for residential use when specified conditions are met, and it adds new sections to chapters 64.32, 64.34, 64.38, and 64.90 RCW that prohibit certain associations from creating governing-document provisions that effectively prohibit those units. The association prohibitions apply to apartment owners (ch. 64.32), condominium associations (ch. 64.34), homeowners' associations (ch. 64.38), and common interest community associations or declarants (ch. 64.90) located in cities subject to the new planning requirement. The new planning provision conditions allowing a mobile dwelling unit on a lot: there must already be an existing housing unit on the lot; the lot must be within an urban growth area; the city or county and utilities must determine existing sewer systems can serve the additional demand; and the unit may not be located in state shorelines or in critical areas or natural resource lands designated under RCW 36.70A.170. Technical requirements include electrical hookup by a dedicated 20-amp minimum GFCI-protected circuit, specified potable water and sewer connection methods if the unit has plumbing, and 24/7 access to potable water, toilets, and showers in the existing home if the unit lacks internal plumbing. Cities and counties must enforce standard inspection procedures for utility hookups but may not require inspection of the mobile dwelling unit itself; they may inspect storage tanks and sewer/sanitary connections. The unit must be maintained so it can be moved at any time and must meet the underlying zone setbacks. "Mobile dwelling unit" is defined to include travel trailers, fifth-wheel trailers, folding camping trailers, truck campers, tiny houses with wheels as defined in RCW 35.21.686, and motor homes. Legally, this is a new land use and procedural statutory requirement and a prohibition on private association restrictions, not a criminal provision or penalty change. Sections adding prohibitions in chapters 64.32, 64.34, and 64.38 each state they expire January 1, 2028; the effective date for the new provisions is not specified in the provided text, and the expiration status of the new section in chapter 64.90 and of the new section added to chapter 36.70A RCW is unclear. The extracted text does not include any other enforcement mechanisms, penalties, or administrative procedures beyond the inspection authority described.

If enacted, people who own a house on a residential lot inside an urban growth area could legally add one towable or vehicle-style mobile dwelling (like a travel trailer, tiny house on wheels, or motor home) on that same lot when sewer capacity is confirmed and the lot is not in a shoreline or protected critical area. Homeowners would likely pay for a dedicated, protected 20-amp electrical hookup and any needed potable water or sewer lateral connections (or rely on 24/7 access to the main house’s plumbing if the unit has no internal plumbing). Cities and counties would need to allow these placements, enforce standard inspections of utility hookups and sewer connections, and ensure units meet setbacks and remain movable; they may face modest new inspection and coordination work with utilities to confirm sewer capacity. The groups most affected are homeowners/property owners, local governments, utilities, and common-interest associations. Homeowners gain a cheaper, flexible housing option but take on hookup and maintenance costs and must keep the unit movable and within setbacks. Cities and counties take on responsibility and some administrative cost to process allowances and inspect hookups. Utilities must assess sewer capacity which could reveal upgrade needs. Apartment, condominium, and homeowners associations are temporarily barred from drafting rules that effectively prohibit these units through January 1, 2028 (the status of the provision for common interest communities and the bill’s effective date or any longer-term sunset for the main planning rule are unclear from the provided text), and the bill does not specify enforcement penalties or many implementation details.