Things to Be Aware of When Constructing an Accessory Dwelling Unit in Washington
Washington residents can finally say goodbye to the arduous process that once dominated ADU construction in the Evergreen State. Recent laws in Washington have made it much easier to install an ADU, or two, on your property. While putting an ADU on your Washington property is easier than ever before, there are still things you should be aware of during your ADU construction process, such as:
Permits needed to construct an ADU in Washington
How long the permit process takes
ADU requirements in Washington
What Permits Are Needed to Construct an ADU in Washington?
You will need a few permits to construct your ADU in Washington. Whether you’re building a unit attached to your home or a detached unit, you’ll need a construction addition/alteration permit.
For Washington residents, there are a couple of resources to help with understanding the permit process, including:
The ADU Building Plans Handout
The ADU Universal Checklist
The Inspection Checklist for ADUs
Permits for ADU construction can be found on your ADU Universal Checklist. Building plans must be submitted to obtain a permit.
How Long Does the ADU Permit Process Take?
New laws in Washington allow for a faster and easier permitting process. There are 10 ADU building plans that are pre-approved by the state of Washington. If you choose one of these pre-approved builds, you can expect to receive your permit in 2-6 weeks. It may take longer to receive your permit if you do not choose one of these pre-approved building plans.
Accessory Dwelling Unit Requirements in Washington
In Washington, you can build separate living spaces in single-family and lowrise zones, and in some cases, neighborhood or commercial zones. Requirements to construct an accessory dwelling unit in Washington include:
You may construct up to two ADU’s in SF5000, SF7200, and SF9600 zones. It’s your choice whether you’d prefer two AADUs or one AADU and one DADU. But the second unit you construct must follow specific criteria to either 1) meet green building standards or 2) be reserved for income-eligible households. Only one AADU or DADU is permitted for each rowhouse, single-family, or townhouse unit in Residential Small Lots (RSL) and multifamily lowrise zones. ADUs are never allowed in apartments in lowrise zones, but they are permitted in apartments in RSL zones.
Parking is no longer required for accessory dwelling units, but you cannot remove existing off-street parking space(s) unless replaced somewhere else on the property.
The property owner does not have to live on the property where an ADU is located.
Seattle Department of Construction (SDCI) reports all ADU permits to King County for sewer treatment capacity charges. You are required to fill out a form acknowledging those capacity charges during your application.