ADU, Accessory Dwelling Units

• Property owners can build ADUs on property in the Low-Scale Neighborhood and Medium-Scale Neighborhood zoning districts. It may also be possible to build ADUs on property in the Mixed-Use Neighborhood and Regional Activity Center zoning districts, but it is less likely because of the higher density requirements.
  • Learn about a property and its zoning district using the Clark County Assessor’s Property Information Center. For instructions, see the Property Information Lookup page. 
• ADUs may be attached, detached, or a combination of both, or may be conversions of existing structures.
• Detached ADUs must be at least 10 feet away from all other structures (primary residence, garage, sheds, etc.) or need to meet additional building code requirements.
• ADUs must be located on the same parent lot as a single-family house, duplex, triplex, fourplex, townhome or rowhome.
• Per state law, Vancouver and many other Washington cities must allow up to two ADUs on any residential lot.

ADUs can be used by the property owner, rented, or can be sold as individual units to allow more households to own a home. There will likely be a mix of opportunities for both sale and rent.

ADUs used as rental units must be registered and periodically inspected.

• Up to two ADUs can be built on a lot.
• If more than two additional housing units are proposed, they may still be allowed, but no more than two of them can be considered ADUs.

• A dwelling unit must be 1,000 square feet or less to be considered an ADU and qualify for reduced impact fees.
  • Dwelling units larger than 1,000 square feet, may still be allowed, but are not considered an ADU.
• The gross floor area of an ADU must not be less than required by the Washington State Building Code.

• The development standards for an ADU will depend on the “building type” of the principal dwelling unit. Building types are defined in the zoning code (section 20.420) and each have their own set of development standards.
• Like all dwelling units, there are no minimum vehicle parking requirements for ADUs. However, there are requirements for the location of parking and allowable material if the property owner does choose to build parking.

• Impact fees for ADUs are 50% of the principal dwelling unit’s impact fees.
  • If the principal dwelling unit is an existing structure, the impact fees for the ADU will be calculated based on the impact fee of the principal dwelling unit as if it were built at the same time as the proposed ADU.
• See section 20.450.030 Impact Fees of the zoning code for additional details.

• Independent access to the ADU via a separate lockable door is required. Convenience doors allowing passage between the ADU and main home are allowed, but cannot be the primary access, except when the ADU is located entirely within an existing home.
• Detached ADUs must be at least 10 feet away from all other structures, including the primary residence and stairs, decks, garage, sheds, etc. or need to meet additional building code requirements such as sprinklers or 1-hour fire-rated construction.
• Attached ADUs must be fully separated from the main unit with STC/IIC 45 sound rating and 1-hour fire-rated construction. This applies to walls as well as floor/ceiling between stacked units.
• An interior conversion ADU located entirely within an existing home, may not need to meet separation requirements or require independent access when there is ceiling height of at least 6 foot 8 inches, legal egress windows, and hard-wired interconnected smoke detectors throughout the entire home and ADU. This does not apply to detached ADUs or additions where the existing home footprint is enlarged.
• Energy Code: Washington State requires new dwelling units to be fully insulated, use efficient heating systems, and select from a number of efficiency credits based on the size of the unit.

Depending on your local utilities, some services may be shared between your home and one or two ADU. When utilities are shared, each unit requires separate shutoffs.

Considerations per utility:

• Heating: Each unit requires independent temperature control
• Power: Will the proposed new ADUs require an upgrade to power service or an expanded meter or utility box? Does your power utility require separate connections or meters for each unit? Contact Clark PUD.
• Water: Are separate water connections and meters are necessary for your proposed development?
• Sewer: If on sewer, does the sewer provider have a site plan showing the location of the existing sewer line? Are you able to connect one or two ADUs to the existing line on your property or will separate lines be required?
• Septic system: If on septic, does the local Health District have a copy of your existing septic system permit, including a site plan showing the location of the septic system and its capacity? Can the existing system be used for the proposed ADUs? If not, what are the options to update the septic system or connect to sewer.
• Gas, cable, internet, and other: What services are available on your property?

• The property owner is not required to live on the property where an ADU is located.
• An ADU does not need to be visually subordinate to the principal dwelling unit, nor aesthetically compatible with the principal dwelling unit.