Go Far®What HB 1337 is
House Bill 1337, signed in 2023, is Washington’s statewide accessory-dwelling-unit reform. Rather than leaving ADU rules entirely to each city, it sets a floor of homeowner rights that every city and county inside an urban growth area must meet as they update their comprehensive plans and development codes — a rollout that has now reached nearly every city we build in, from Lynnwood and Everett to Seattle and the Eastside. If a local code is more generous than the state floor, the local code stands; if it is more restrictive, the state floor wins.
The six big changes for homeowners
- Two ADUs per lot. Cities must allow at least two accessory units on lots that allow a single-family home — for example an attached ADU plus a detached backyard cottage (DADU), or two attached units. One house can become three homes on one lot.
- No owner-occupancy requirement. Cities can no longer require you to live in the main house (or the ADU) for the unit to be legal. You can rent both long-term, house family, or move away and keep the property — the choice is yours. Cities may still regulate short-term rentals.
- Capped impact fees. Impact fees on an ADU cannot exceed 50% of what the city would charge for the main house, which meaningfully trims soft costs — see our ADU cost guide for where fees fit in the budget.
- Real height allowances. Cities can’t cap ADU height below 24 feet (unless the main house is capped lower) — enough for the two-story cottages that make small footprints livable.
- Friendlier parking rules. Cities can’t demand more than one off-street stall per unit on most lots, and can’t require any ADU parking within half a mile of a major transit stop — a big deal near light rail in Lynnwood, Mountlake Terrace, and Shoreline.
- No stricter design standards. Setbacks, lot coverage, and aesthetic rules for an ADU can’t be tougher than what applies to the main house, and cities must allow ADUs of at least 1,000 square feet.
What cities can still require
HB 1337 is not a free-for-all. Your project still goes through normal permitting, building code, and inspections. Cities can still require connection to public sewer where available, apply critical-areas rules (steep slopes, wetlands, shorelines), and restrict using ADUs as short-term rentals. And outside urban growth areas — rural unincorporated land — the law doesn’t apply, though many counties allow ADUs there under their own rules.
What it means in Snohomish & King County
Most cities in our service area have now folded HB 1337 into their codes, and several — Seattle above all — were already ahead of it. The practical effect we see on real projects: more lots qualify, the approval conversation is shorter, and configurations that used to be non-starters (a rented cottage behind a rented house, a two-story DADU on a modest lot) are now routine. City-level details still matter — our guides to Lynnwood & Snohomish County rules and Seattle’s ADU rules cover the local specifics.
Is your lot ready?
The best first step is a site check: lot size and coverage, sewer location, access, trees, and slope determine more than zoning does. Go Far Construction designs and builds ADUs, DADUs, and garage conversions across Snohomish and King County, and we’ll tell you honestly what your lot supports before you spend a dollar on drawings. Budgets run from a garage conversion at the low end to a full custom cottage — our DADU cost guide and ADU financing guide put numbers on it. Request a free estimate and we’ll walk your lot with you.