ADU rules in Bellevue

Bellevue's zoning ordinance has no accessory dwelling unit use, and every residential district allows "only one building for living purposes" per zoning lot. Guest houses "not rented or otherwise conducted as a business" are a permitted accessory use in AG, RA, RE, RS-120, RS-84, RS-72, RD-60 and the RG districts, but the term is undefined; the code's defined term for living quarters in an accessory building, "accessory living quarters", must have no kitchen facilities and may not be rented or used as a separate dwelling unit. A detached backyard home with its own kitchen is therefore not allowed; a kitchenless guest house for visiting guests is.

In the single-family districts (RS-120, RS-84, RS-72, RE, RA) a single-family dwelling is defined as a building with one dwelling unit, so no internal or attached second unit is allowed. The only route to a second attached unit is a two-family dwelling (duplex), a permitted use by right in RD-60 on lots of at least 12,000 sq ft and 80 ft wide, and in RG-50, RG-28, RG-20 and RG-8 on lots of at least 10,000 sq ft. That is a duplex conversion or build, not an accessory unit, and most single-family lots in those districts are 5,000 to 6,000 sq ft.

Because no ADU use exists, the only size rules that reach a guest house are the general accessory-building limits. On lots of one acre or smaller the footprint may be no larger than the greater of 750 sq ft or 50 percent of the principal building's footprint, never more than 1,200 sq ft; on larger lots the cap is 1,200 sq ft. Accessory buildings are 15 ft tall at most (one more foot per two feet of extra setback, never taller than the house), sit 5 ft from side and rear lines, stay out of the front yard, and count toward district ground coverage (30 percent in RS-72). A two-family dwelling in RD-60 or RG has no unit-size cap beyond the district floor area ratio and coverage limits.

No owner-occupancy rule appears anywhere in the zoning ordinance. The two-family dwelling route has no owner-residency condition, and the code's definition of a dwelling unit contemplates "owner occupancy or lease on a weekly, monthly, or longer basis". A guest house is tied to the household only through the bar on renting it.

The Group A parking table requires off-street parking for "Dwellings: One (1) for each" (the row is printed truncated in the ordinance), read as one space per dwelling unit, so a two-family dwelling needs two spaces. Each district also requires off-street parking for all uses established in it. No parking standard is written for guest houses. Parking areas must be hard-surfaced (concrete or asphalt).

Guest houses are a permitted accessory use and two-family dwellings a permitted principal use in their districts, so either needs only a building permit, with Planning Department zoning review and no hearing. Nothing ADU-like is listed as a conditional use (which in Bellevue needs a Planning Commission recommendation and City Council approval). A self-contained second unit in a single-family district would need a rezoning or a text amendment.

Every residential district limits guest houses to those "not rented or otherwise conducted as a business", and accessory living quarters may not be "rented or otherwise used as a separate dwelling unit". A unit in a two-family dwelling may be leased; the dwelling unit definition covers lease "on a weekly, monthly, or longer basis". The Bellevue City Code (American Legal, 2026 S-12) has no short-term rental licensing or registration chapter, and bed and breakfasts are a conditional use in residential districts.