Accessory Dwelling Units - Additional Help for Affordable Housing?

Accessory Dwelling Units (ADUs), also known as "mother-in-law apartments" or "backyard cottages," are smaller homes built on the same property as the main house. In Washington State's 2025-2026 legislative session, lawmakers are considering several bills to use ADUs to help address housing issues. Here are four key proposals:

House Bill 1010 aims to allow for ADUs in rural areas. This bill proposes permitting detached ADUs outside urban growth areas, which are regions designated for development. If passed, it would enable property owners in rural communities to add ADUs to their land, potentially increasing housing options in less populated areas. 

House Bill 1345 seeks to establish limitations on detached ADUs outside urban growth areas. This bill aims to regulate the development of ADUs in rural regions to ensure that they align with local planning and zoning regulations. The goal is to balance the need for additional housing with the preservation of rural community characteristics. 

Senate Bill 5413 is a companion to HB 1345, introduced in the Senate. It also focuses on setting limitations for detached ADUs outside urban growth areas, aiming to provide more housing flexibility in rural parts of the state while maintaining appropriate land-use planning. 

House Bill 1353 proposes establishing a self-certification program for ADU project permit applications. This means that qualified professionals, such as licensed architects, could certify that ADU plans meet local requirements, potentially speeding up the approval process and reducing costs for homeowners interested in building ADUs.  

If these bills pass, they could lead to more ADUs being built across Washington State. This increase in housing options might help address housing shortages by providing more affordable and flexible living spaces.