Home Remodeling in
Olympia, WA

Olympia allows up to two accessory dwelling units on a residential lot alongside the main house, in every residential district. Each one can have up to 1,000 square feet of gross floor area.

A covered porch or patio does not count toward that figure, up to 120 square feet per ADU, as long as it stays open. An ADU can also be attached to a garage or shop building, in which case the ADU keeps its 1,000 square feet and the garage or shop can be up to 800 square feet, or larger where the zone allows it.

Detached ADUs are limited to 24 feet in height. They cannot sit in a required side yard and must be five feet from the rear property line, or right on it where the lot backs onto an alley.

Olympia makes it easy to turn an existing building into an ADU. Legally built structures completed before 22 December 2025, or at least ten years old at the time of application, can be converted even if they break today's setback or lot coverage rules. That includes detached garages.

The converted building can even be added onto, provided the addition does not make the nonconformity worse. The city can also allow an entire floor of a house that is at least two years old to become an ADU, even if that floor is over 1,000 square feet.

One more option is unusual: on a lot where the existing house is 1,200 square feet or smaller, that house can become the ADU when a new main home is built on the same lot.

Most cities require an ADU to stay in the same ownership as the main house. Olympia allows an ADU to be sold independently once a condominium or unit lot subdivision has been approved and completed.

That changes the numbers on a project. A backyard unit can be planned as a future sale rather than only as a rental, which is worth deciding before design, because the subdivision route has its own requirements.

ADUs are still subject to the same lot coverage and tree density rules as a new house, and they need to be oriented to protect neighbours' privacy as far as practical.