Accessory Dwelling Units

An Accessory Dwelling Unit (ADU) is a small, self-contained residential unit located on the same lot as an existing single-family home.  ADUs have all basic facilities needed for day-to-day living independent of the main home, such as a kitchen, sleeping area, and a bathroom.  ADUs are classified as two types:

• -     Attached Accessory Dwelling Units (AADU) where the ADU is attached internally (like converted basement or attic) or via an addition to the existing  single-family structure; or
• -     Detached Accessory Dwelling Units (DADU) where the ADU is a separate structure on the lot (including detached garages with living spaces).

Depending on the use or ownership, water meters serving ADUs fall into one of two District policies: Common Meter Policy or Separate Meter Policy.  For a description of ADU policies, please see HERE.

Applicants should carefully evaluate their intended use of an ADU to determine what policy should apply in their situation.   ADUs converted into a condominium or other type of independent ownership separate from the principal unit will trigger the Separate Meter Policy and is required to have a separate water meter to each structure.  It is recommended that applicants who intend to sell, transfer, or separate ownership of an ADU now or in the future install a separate meter at the time of ADU construction or conversion.  

For questions on Highline Water District ADU Policy, please contact Delylah Silva, DE Coordinator, at 206-592-8924 or dsilva@highlinewater.org.