What is an ADU/DADU?

An ADU – or Accessory Dwelling Unit – is a self-contained housing unit that shares the footprint of the primary residence. ADUs may be a converted garage, basement, attic, or simply an apartment. A DADU – or Detached Accessory Dwelling Unit – is a self-contained housing unit that stands on its own on the property.
Features of ADUs and DADUs include:

  • Completely separate living units from the main house – includes separate entrance
  • There may be size limitations depending on your location
  • They have their own kitchen and bathroom facilities
  • Also depending on location, they may have fire suppression requirements combined with or separate from the primary house, requirements for water heater access, electrical and water shutoff, and more. Location matters when determining what is required.

It is important to know these requirements because simply having a separated living space does not make it an ADU that is legal and can be rented as such. Furthermore, ADUs/DADUs are not permitted in all areas. HOAs, critical areas, areas on septics, etc, may have additional ADU/DADU requirements or may not permit them at all. For example, an HOA may have in their bylaws that an ADU that appears like it is part of the house is okay, but a stand-alone DADU structure is not.

ADUs/DADUs are regarded as a way to help add more housing units which will help stabilize housing prices including rent. In 2023, House Bill 1337 was signed into law which will loosen up ADU/DADU housing restrictions significantly. 

This bill allows for two ADUs/DADUs plus a primary residence for every single-family lot with a few exceptions. Cities and Counties will be updating their Comprehensive Plans in the next three years and as a requirement, must change their codes to allow for ADUs/DADUs within six months. In Bellingham and Whatcom County, the Comprehensive Plan Deadline is June 30, 2025, which means the deadline for implementation of these two bills is January 1, 2026. However, there is nothing stopping the cities and counties from adopting any or all aspects of the bills early.

Since I expect there to be significant demand for services such as ADU/DADU design, permitting, and construction as we approach the 2026 deadline in Whatcom and Skagit Counties, if you are considering adding an ADU or DADU to your property, getting prepared ahead of time is smart. Get your ducks in a row now to keep your expenses lower than they will be at the height of demand.

Stay Updated

Want to stay up-to-date on the ADU/DADU ordinances in your area or want to start planning? Fill out the form below!