ADU Rules on the Eastside: Bellevue, Kirkland and Redmond

Three cities, ten miles apart, three different answers. If you are planning a backyard cottage on the Eastside, the city line matters more than almost anything else about your lot.

Kirkland has allowed two ADUs with no owner-occupancy requirement since 2020. Bellevue did not allow a detached ADU at all until July 1, 2025. Redmond has rewritten its ADU chapter twice in eighteen months. The state floor is the same everywhere; everything above it diverges.

Below is what each city actually allows in 2026, which number binds first, and the handful of places where the published code and the published guidance disagree — because on the Eastside they do.

Current as of October 2026, from each city's adopted code. Several recent ordinances were still pending codification when we checked, and those are flagged. Confirm anything load-bearing with the city before you design to it.

What state law guarantees in all three

Washington's ADU statute sets a floor that no city inside an urban growth area can go below. This is the backstop when a city's own page says something more restrictive:

• Two ADUs per lot, and both of them may be detached.
• No owner-occupancy requirement.
• No floor-area cap below 1,000 square feet, and no roof-height cap below 24 feet.
• No ADU-specific setback, lot-coverage, tree-retention, entry-door, aesthetic or design-review standard that is stricter than the one applied to the principal house.
• A detached ADU must be allowed at a lot line that abuts a public alley.
• No parking required within half a mile of a major transit stop, and at most one space per unit on lots under 6,000 square feet.
• Impact fees capped at 50 percent of what the principal unit would pay.
• No ban on selling an ADU as a condominium unit solely because it was built as an ADU.

We cover the statewide picture in more depth in Washington ADU laws explained. The rest of this article is what the three cities do on top of it.

Bellevue: newest to detached ADUs, and the tightest on height

Bellevue's land use code read “shall not be a detached structure” until Ordinance 6851 took effect on July 1, 2025. That single change is why Bellevue has the thinnest track record of the three and the most out-of-date public information.

Which brings up the first practical warning: the City's own ADU web page is stale. When we checked it in October 2026 it still said an ADU may not be in a detached structure, and it claimed a 30-day minimum rental term. Neither matches the adopted code, and we found no current code basis for the 30-day claim. The code governs. If a planner quotes the web page back to you, ask for the code section.

How many, and how big

Two ADUs per lot in any district that allows a single-family dwelling, in any combination of attached and detached. A later 2026 ordinance extends that to middle-housing lots. Each ADU is capped at 1,200 square feet of floor area, plus up to 300 square feet per unit of parking or unheated storage that does not count against the cap. The director can go above the cap for a whole single floor of the house, or for an addition to or conversion of an existing detached accessory structure.

The floor-area-ratio trap

This is the Bellevue rule that surprises people. An attached ADU's floor area is excluded from the lot's FAR calculation. A detached ADU is not — it counts toward FAR, and it counts as a dwelling unit for the purpose of reading the FAR table. On lots of 10,000 square feet or less that moves you from the one-unit row to the two-unit row, so the allowance goes up, but the cottage is spending from the same pool as the house. A DADU also counts toward the maximum number of units on the lot; an attached ADU does not.

On a lot where the house is already large, this is frequently the binding constraint — not the 1,200 square foot cap.

Height: 24 feet

Bellevue caps a detached ADU at 24 feet measured to the highest point, or 28 feet as an addition over an existing accessory structure. That is exactly the statutory floor, and the tightest of the three cities. For contrast, Bellevue's middle-housing buildings get 32 feet flat or 35 feet pitched. The code section setting the 24 feet does not state the baseline grade the measurement runs from, which matters a great deal on a sloped lot — get that confirmed in writing before you draw a roof.

Setbacks, coverage and trees

Other dimensional standards follow the middle-housing table: front setback 25 feet in the least dense district, 20 in the next, and 10 feet in the single-family districts from SR-1 and denser; rear 15 feet in the four least dense districts and 10 beyond that; side 5 feet everywhere. A detached ADU may sit at an alley lot line. Lot coverage runs 40 to 45 percent by district, with separate impervious and hard-surface caps on top of it.

Trees are often the real design driver. Bellevue treats a tree of 6 inches diameter as significant and 24 inches as landmark, with lower thresholds for particular species and alder and cottonwood excluded. Review triggers on any application that changes lot coverage by more than 20 percent or adds more than 20 percent impervious surface — a DADU almost always does. The city then requires a minimum number of tree credits per 1,000 square feet of canopy site area, and because a DADU counts as a dwelling unit the lot is read in the lower “two or more units” column. Retained trees earn 2 credits at 6 to 10 inches up to 10 credits at 24 inches or any landmark tree, with alder, cottonwood and property-line trees at half value. A 2026 ordinance cut the SR-1 requirement from 5 and 4 credits to 2 and 1.5. A fee in lieu is available; the figure we found was around $1,300 per credit, from a code host rather than the city's own schedule, so verify it. An arborist report is required with the permit.

Parking, permits and how long it takes

No parking required for an ADU under 1,000 square feet excluding the garage, none within half a mile of a major transit stop, otherwise one space. Owner occupancy was removed in 2023. There is no minimum lot size.

You apply as a new one- or two-family structure through MyBuildingPermit, with valuation-based fees and plan review at 65 percent of the inspection fee. Credit to Bellevue here: it publishes actuals rather than targets — a median of 164 days for a new single-family permit and 76 days for a single-family addition over the twelve months to October 2026. A pre-approved plan program for DADUs up to 1,200 square feet and 24 feet is in development, discussed at a Council study session in March 2026, with launch tied to the next state building code update. Not available yet.

One genuinely useful Bellevue feature: a unit lot subdivision is available on a lot with an attached or detached ADU, which is a cleaner ownership path than Seattle offers.

Kirkland: the most permissive, and it got there first

Kirkland allowed two ADUs and dropped owner occupancy in 2020, years ahead of the state mandate, and the code reads like a city that has had time to work the kinks out.

How many, and how big

Two ADUs per single-family dwelling, both of which may be detached (the Residential-L shoreline environment is limited to one). The cap is 1,200 square feet of gross floor area, excluding areas with ceilings under 5 feet, uncovered rooftop decks and at-grade patios, plus up to 200 square feet of covered or uncovered exterior elements.

The FAR break that makes Kirkland generous

This is the best provision for an ADU anywhere on the Eastside: the first 500 square feet of a detached ADU is excluded from floor area ratio on lots under 8,500 square feet, and the first 800 square feet on lots of 8,500 square feet or more, provided the structure sits behind the main house. On a lot where FAR is the binding constraint — which, as in Bellevue, is common — that exclusion is worth more than any size cap.

Height and setbacks

Height follows the zone rather than the ADU: 25 feet above average building elevation in RS, 30 feet in RSX and RSA. The old rule capping a DADU at 15 feet above the main roof peak, whichever was less, is gone from the current text — worth knowing, because it still circulates in older guides.

Yards are front 20, rear 10, side 5 minimum with 15 feet combined. There is a useful allowance letting a detached ADU come within 5 feet of the rear line where the portion inside the required rear yard stays at or under 15 feet above average building elevation, and to the line at an alley provided the eaves do not cross it. Lot coverage is 50 percent in RS. Conversions of existing structures, including detached garages, are exempt from current setbacks and coverage as long as the nonconformity is not increased — which makes a garage conversion a genuinely strong play in Kirkland. There is no minimum lot size and no ADU design standards; the old “entrance clearly secondary” requirement is gone.

Parking is the one ambiguous item

Kirkland's parking chapter was amended in April 2026 to exempt ADUs from minimum parking outright. But the codified ADU section still carries the older transit-proximity and on-street-availability language, and a September 2026 ordinance was pending codification when we checked. Our read is that there is effectively no minimum, but this is one to confirm with the city rather than assume. For the Seattle comparison, see Seattle ADU parking rules.

Impact fees changed in July 2026

This one costs money, so note the date. ADUs of 800 square feet or less remain exempt from impact fees, but complete ADU building permit applications received on or after July 1, 2026 are charged, phased in through 2027. If you are over 800 square feet, build the fee into the budget rather than assuming the old exemption.

Trees, ownership and pre-approved plans

Regulated trees start at 6 inches diameter and landmark trees at 26 inches, with a critical root zone of one foot of radius per inch of diameter and a minimum density of 50 tree credits per acre covering the house and accessory structures. Fee in lieu is $450 per credit. Kirkland then does something neither of the other two cities states as plainly: the code says the City will not require retention that would preclude the ability to construct ADUs consistent with the ADU section. On a treed lot that sentence is worth a lot. Compare it with how Seattle handles the same conflict in Seattle's tree protection rules.

An ADU may be segregated in ownership, and non-stacked ADUs may be subdivided within a unit lot subdivision. ADU registration requires a covenant recorded with King County. Kirkland has run a live pre-approved DADU program since March 2023, with the designer fee capped at $1,000 — the named designs include The Schooner, Cedar Cottage, Sedge Cottage and The Family. Published review targets are five weeks for a first review, ten business days on fast track, three business days on express. Targets, not actuals.

Short-term rental is allowed city-wide under its own ordinance: rentals under 30 days with state and city licences, where the owner or agent is in residence at least 245 days a year for unlimited renting with a maximum of two concurrent rentals, otherwise a 120-day annual cap. That is more permissive than most of the region.

Redmond: rewritten twice, with the tightest size cap and a height question

Redmond reorganised its zoning code in June 2025, moving ADUs to a new chapter, then amended that chapter again in 2026. The old rules — one ADU, 1,000 or 1,500 square feet, 25 foot detached height, one parking space, owner occupancy for rentals under twelve months — are gone entirely. Anything you read that cites the old chapter is obsolete.

How many, and how big

Two ADUs or tiny homes per residential lot, attached or detached, with no restriction on both being detached; a tiny home is 400 square feet. The cap is 1,000 square feet — the tightest of the three, and exactly the statutory floor. The Administrator may allow more where the ADU occupies an entire single floor of the house, or where the lot exceeds 10,000 square feet and the unit is affordable or provides a public benefit.

Then there is the rule that binds before the cap does on a modest house: total accessory-structure footprint may not exceed 60 percent of the principal dwelling's ground-floor living area, excluding the garage. On a 1,400 square foot single-storey house that is 840 square feet of accessory footprint for everything — cottage, shed and detached garage combined. Run this number before you run the 1,000 square foot one.

The height trap

Redmond caps accessory structures at 22 feet, but expressly excepts accessory structures containing an ADU, sending them to the zone maximum instead — which in the neighbourhood residential zone is 38 feet. On its face that is far more generous than Bellevue's 24 feet or Kirkland's 25.

We are flagging it rather than celebrating it. A 38 foot backyard cottage would be an outlier in the region, and a reading that generous is the kind of thing a city clarifies in the next amendment cycle. Confirm it with Redmond planning in writing before you design to it, and do not let anyone sell you a three-storey DADU on the strength of a code cross-reference.

Setbacks, coverage and fees

In the neighbourhood residential zone: front 10 feet, street side 10, interior side 3, rear 5, alley 2, with 5 feet of building separation. A detached ADU may sit immediately against a lot line abutting a public alley or right-of-way. Coverage is 50 percent, or 60 on lots of 18,000 square feet or less with three or more units; impervious 70 percent; minimum open space 20 percent; minimum lot size 3,000 square feet. Total gross floor area is capped by unit count, starting at 4,500 square feet for one unit and 6,000 for two, and below-grade area counts toward it — whether an ADU counts as a “dwelling unit” for that table is not stated, which is another question for the city.

Parking for an ADU is zero. And Redmond is the most generous of the three on fees: ADUs are exempt from all impact fees, beyond the 50 percent cap state law requires. For scale, 2026 principal-unit fees run roughly $10,100 transportation, $6,800 parks and $7,300 school — so the exemption is real money. Permit fees themselves are valuation-based with plan review at 65 percent and a 4 percent technology surcharge. Redmond publishes no review-time targets and has no pre-approved plan program.

Two Redmond items that can bite

• Trees: at least 35 percent of significant trees (6 inches and up) must be retained, landmark trees over 30 inches cannot be removed without a granted exception, and structures have to stay at least 5 feet outside the drip line of a protected tree. On a developed single-family lot you need a permit to remove any significant tree, with an annual allowance of 2 to 8 trees depending on lot size. There is no ADU-specific exemption — unlike Kirkland.
• Sprinklers: Redmond’s residential permit page states that sprinklers are required in new homes and in detached ADU units. That is a cost line Seattle does not have, and it is worth confirming with Redmond for your specific design before you budget.

Middle housing in Redmond allows six units per lot, or eight where one is affordable at or below 80 percent of area median income — above the state minimum. Whether the two ADUs sit inside that six is not stated in the code we read. If you are thinking about more than a house plus a cottage, that answer changes the whole plan.

Side by side

• Size cap: Bellevue 1,200 sq ft (plus 300 sq ft of storage or parking); Kirkland 1,200 sq ft with generous exclusions; Redmond 1,000 sq ft, with a 60 percent accessory-footprint ceiling that often binds first.
• Height: Bellevue 24 ft; Kirkland by zone, 25 ft in RS; Redmond reads to the 38 ft zone maximum — confirm before relying on it.
• Floor area ratio: Kirkland excludes the first 500 to 800 sq ft of a detached ADU; Bellevue counts a detached ADU fully; Redmond uses a unit-count GFA table instead.
• Impact fees: Redmond exempt; Kirkland exempt at 800 sq ft or less, charged above that for applications from July 1, 2026; Bellevue at the statutory 50 percent cap.
• Trees: Kirkland protects your ability to build the ADU; Bellevue runs a credit system a DADU almost always triggers; Redmond requires 35 percent retention with no ADU carve-out.
• Pre-approved plans: Kirkland live since 2023; Bellevue in development; Redmond none.
• Published timelines: Bellevue publishes actual medians (164 days new single-family); Kirkland publishes targets; Redmond publishes neither.

Which number actually binds your lot

The size cap is almost never the constraint that decides a project. In our experience the order is:

• Floor area ratio or the accessory-footprint ratio, which is set by how big your house already is.
• Tree retention and critical root zones, which is set by what is growing where you wanted to build.
• Lot coverage and impervious surface, which the driveway and patio have usually already spent.
• Setbacks and building separation, which decide the footprint shape.
• Height, which usually only matters if you want a loft or a second storey.
• The size cap, which you often never reach.

That is why a feasibility check beats a floor plan as a first step. The same logic applies in Seattle, where the binding number is usually floor area rather than the headline size limit — see how big a DADU can actually be in Seattle.

Confirm these before you design

Being honest about the edges is more useful than pretending the code is settled. These are the items we would put in writing to the city on any Eastside project:

• Bellevue: the grade the 24-foot height is measured from, the current codified text after the mid-2026 ordinances, the actual fee-in-lieu rate per tree credit, and whether anything in the city code restricts short-term rental of an ADU.
• Kirkland: whether the parking exemption is now unconditional after the 2026 amendments, and the current building permit fee basis.
• Redmond: whether the 38-foot reading is really intended for a detached ADU, whether an ADU counts as a dwelling unit for the gross-floor-area table and the six-to-eight unit middle-housing count, and whether the sprinkler requirement reaches your specific design.

One planner email, sent before design starts, is worth more than any article — including this one.

Where DIGS fits

DIGS builds ADUs, DADUs and custom homes across the greater Seattle area, including Bellevue, Kirkland and Redmond. We read the code for your specific parcel before anyone draws anything, because on the Eastside the jurisdiction decides the design more than the design decides itself.

If you want to know what your lot will actually carry, start with a feasibility conversation — or look through our floor plans to see what fits inside 1,000 to 1,200 square feet.