Seattle Legal Duplex vs. Accessory Dwelling Unit (ADU): What is the difference?

Seattle real estate offers various options when searching for a multi-family home to purchase. If you are in the market for a home with two dwelling units, you will find both legal duplexes and Accessory Dwelling Units (ADU) for sale in Seattle. Knowing the details and legal restrictions of each variation will help you decide which option will best suit your needs.

For a single dwelling with two living units to legally function as a duplex in the city of Seattle, comprehensive zoning laws must be followed. Any duplex built within the last 40 years must be zoned for multi-family use; Lowrise 1 (LR1), Lowrise 2 (LR2) and Lowrise 3 (LR3) are the most common zones in the Seattle area. Duplexes with valid parking and lot coverage are legal in these zones and may be rented to tenants for investment purposes.

Seattle’s comprehensive zoning laws came into effect early in the 20^th century. Prior to these zoning laws, various duplexes were built in areas now zoned exclusively for single-family dwellings. A single home consisting of two living units within one of these areas is grandfathered as a legal duplex only if permit evidence confirms the home functioned as a duplex before zoning laws were in effect. Information on permits and zoning may be found at City of Seattle's Department of Planning and Development. 

Much like a duplex, an ADU consists of separate dwelling spaces. A legal ADU may be located in a single-family zone provided that the property owner occupies one of the units as a primary resident. The property owner may not move out and rent out both units to tenants.

To establish an ADU in Seattle, the owner must obtain a permit and sign and record an owner-occupancy covenant. Any unauthorized ADU may be shut down by the city. Consult the City of Seattle for more information regarding Attached ADUs and Detached ADUs

City housing inspectors maintain strict enforcement to ensure that ADU property owners comply with government restrictions. Neighbor complaints or renting out units in an illegal duplex result in result in tenant eviction, removal of the second kitchen, and stiff fines.

Before submitting an offer on a duplex or ADU in Seattle, confirm the property's zoning and permit history with the city to ensure compliance with applicable laws in terms of renting out both units. Doing your own research prior to purchase can also prevent any possible complications with reselling the home in the future. 

Thinking about converting your current primary residence into an operating ADU? Be sure to obtain legal authorization from the City of Seattle and divulge all pertinent information to future homeowners when selling the property.