Washington Is Now the National Leader in ADU Policy — Here’s What That Means for Builders

Washington’s HB 1337, which took full effect in July 2025, has established the most permissive accessory dwelling unit framework in the country, requiring cities and counties to allow at least two ADUs per residential lot with no owner-occupancy requirements and strong design parity protections. The results are already showing up in permit data: Washington ADUs now represent 62% of new single-family construction volume, and Seattle has become the first major U.S. city where ADU construction is outpacing single-family home building. Oregon isn’t far behind, with ADUs running at 72% of its single-family permit ratio and Washington County actively exploring new rules to allow ADUs on rural residential land previously off-limits. For residential contractors and builders across both states, the ADU pipeline represents one of the most durable near-term opportunities in the market.

Source URL: https://eciks.org/4210-75755-adu-housing-market-hits-21-45b-in-2026-washington-leads-permit-surge-nationwide