ADU rules in Vancouver and Clark County (2026)

The law changed in homeowners' favor

For decades, accessory dwelling units in Washington were legal in theory and strangled in practice: owner-occupancy requirements, parking mandates and size caps killed most projects on paper. House Bill 1337, passed in 2023, dismantled that machinery statewide, and the local codes have now caught up. If you own a lot in Vancouver or urban Clark County, here is what you are actually allowed to build in 2026, with sources, and why the projects finally pencil.

What HB 1337 guarantees, everywhere in the urban growth area

Per the Department of Commerce's guidance on the law, cities and counties inside urban growth areas may no longer:

• Require the owner to live on the property, except for ADUs used as short-term rentals
• Allow fewer than two ADUs per lot, attached or detached, on any lot meeting the minimum size for the principal home
• Cap ADU size below 1,000 square feet of gross floor area
• Prohibit ADUs up to 24 feet tall or two stories, or impose stricter setback and design rules than the main house faces
• Demand off-street parking within a half-mile walk of a major transit stop, or more than one space per ADU on smaller lots elsewhere
• Charge impact fees above 50 percent of what the principal unit would pay
• Prohibit ADUs from being sold separately as condominiums

City of Vancouver: the current rules

The city's ADU page now allows units up to 1,000 square feet, drops the owner-occupancy requirement entirely, and no longer requires the ADU to look architecturally subordinate to the main house. Two units per lot are allowed now, and starting July 31, 2026 the city's lot rules open further, with up to two ADUs among additional structures on a lot. One practical note that survives: an ADU application cannot eliminate the main home's required parking space. Permits run through the same RES permit process as other residential construction, which our permit guide walks through office by office.

Unincorporated Clark County: slightly different math

The county's June 2024 handout for urban ADUs allows 1,000 square feet, rising to 1,500 square feet on lots of at least 20,000 square feet; basement ADUs may use the full basement footprint as long as the ADU does not exceed the primary dwelling's size; and where a lot carries two ADUs, their combined area caps at 2,000 square feet. Rural lots play by older, tighter rules, so if your property is outside the urban growth boundary, we check the current county code before sketching anything.

Why ADUs pencil here now

Three Clark County facts stack up. Home values are high and rising, with the Zillow index for Vancouver around $502,000 as of August 2026, so adding a second dwelling adds real asset value. Demand keeps arriving: migration from the Portland side roughly doubled between 2019 and 2022 per the Oregon Office of Economic Analysis, and renters follow the same tax math owners do. And the rules themselves now permit the versions that earn: no owner-occupancy means a true rental, separate-sale rights create an exit, and detached backyard units up to 1,000 square feet are large enough for real one and two bedroom layouts. What the projects cost to build, by type, with sourced ranges, is in our ADU cost guide.

What an ADU project involves

A detached ADU is a small house: foundation, structure, full kitchen and bath, utility connections, energy code compliance, and its own inspections. Garage and basement conversions reuse the shell and usually cost meaningfully less, with the county's basement allowance above making basements especially interesting in homes that have them. Sales tax applies to the construction contract like any other project here, and the permit path depends on your jurisdiction. Our ADU construction page covers how we scope, price and build them, and the estimate is free.