Since January 2026, many Neighborhood Residential lots can hold four or more homes. A backyard cottage is still one option, and the new rules change how ADUs fit the count.

Large trees often decide where a Seattle backyard cottage can go. An arborist sets the tree protection area, SDCI verifies it and that area shapes the buildable space.

A recorded easement can rule out the best looking spot in your yard. A title report, a survey and King County recorded documents show what runs across your lot.

Seattle does not require off-street parking for accessory dwelling units. If you choose to add a space anyway, location rules, curb cuts and lot coverage still apply.

Seattle allows up to two accessory dwelling units on a lot, in any mix of attached, detached or stacked. Density, coverage, utilities and access decide what actually fits.

A Seattle ADU with up to two bedrooms can reach 1,000 square feet, and one with three or more can reach 1,200. Underground space and some garage area do not count.

Neighborhood Residential lots can cover up to 50 percent with structures, and a backyard cottage counts toward that cap. Low decks, eaves and underground space get exclusions.

In Seattle’s Neighborhood Residential zones a backyard cottage follows the same 32 foot base height as a house, with pitched roof allowances. Grade and setbacks still shape the real envelope.

In Neighborhood Residential zones a backyard cottage can sit 5 feet from most lot lines and right on an alley line. Here is how setbacks shape footprint, windows and entries.

Most Seattle residential lots allow a backyard cottage. Whether yours can fit one comes down to setbacks, coverage, access, utilities, trees, easements and critical areas.