Can an HOA block an ADU?

Sometimes. A covenant recorded before Washington's 2023 ADU law can still limit an accessory dwelling unit, and a single-family use or one-dwelling-per-lot clause often does that without naming ADUs. Since July 23, 2023, an association inside an urban growth area may not adopt a new governing document that limits ADUs more than the city may. So the answer depends on what was recorded, where the lot sits, and when.

What a declaration usually says

Older declarations rarely say "ADU". They say "one single-family dwelling per lot", "no structure other than a dwelling and a garage", or "no business use". Any of those can block a second unit. Newer declarations sometimes address ADUs by name, either to allow them with design review or to forbid them.

What to check before you buy

1. Read the use clause and the structure clause of the recorded declaration for the parcel.
2. Check the recording date of each document against July 23, 2023. A covenant recorded before that date stands; a limit in a document created after it may not be enforceable if the lot sits inside an urban growth area.
3. Confirm the city or county allows an ADU on the lot. The covenant and the zoning code both apply.

Where the law comes in

RCW 36.70A.680 and 36.70A.681 (from House Bill 1337, 2023) require cities and counties that plan under the Growth Management Act to allow two accessory dwelling units per lot inside urban growth areas. RCW 64.90.350, from the same bill, bars a common interest community inside an urban growth area from creating governing documents after July 23, 2023 that restrict ADUs in ways a city may not. Covenants from before that date stay in force. The same section says a city that issues an ADU permit is not liable when the unit breaks one of those later covenants, so a permit does not settle the covenant question.