Kenmore ADU Permit Requirements, in Plain English

The short answer

Can I Build an ADU in Kenmore?

An ADU is an accessory dwelling unit. It is a second, smaller home on the same lot as your house. It can be attached, like a basement apartment or an addition. Or it can be detached, like a backyard cottage. Kenmore calls a detached one a detached ADU. Backyard cottage, in law suite, granny flat, mother in law unit, guest house: if it is a second home on your lot, it is an ADU, and the rules on this page apply.

Kenmore rewrote its ADU rules in 2025. The City Council adopted the changes on June 23, 2025, and they took effect July 1, 2025. The old limits are gone. You no longer have to live on the property. The old one ADU per lot limit is gone. The old 600 square foot cap on small lots is gone. If you read about Kenmore ADUs more than a year or two ago, or you are looking at the city's older ADU checklist, most of what you read is out of date.

Today, on any lot where a single family home is allowed, you can build up to two ADUs in any mix of attached and detached. This page walks through the current rules and the things that actually shape a project.

First, Make Sure Kenmore Is Your Permit City

A Kenmore mailing address does not always mean the City of Kenmore holds your permit. The 98028 ZIP code is shared with neighbors, and some homes with a Kenmore address sit in nearby cities or in unincorporated King County. Each has its own ADU rules.

Before you plan anything, look up your parcel on the city's zoning map or call Development Services. If the City of Kenmore holds your parcel, the rules on this page apply to you.

Know Your Zone

Most single family neighborhoods in Kenmore are zoned R4 or R6. The number is the target density, in homes per acre. Some larger lots and rural feeling pockets are R1. Multifamily areas use R12 and higher. The ADU rules on this page apply wherever a single family home is allowed, but the setbacks, height and hard surface limits depend on your zone, so find yours before you design. Your plat, your old permits and your tax record may all show the zone, but the city's current zoning map is the one that counts.

Confirmed rules

Kenmore ADU Rules: What Is Confirmed

Zoning and How Many Units You Can Build

Kenmore allows up to two ADUs on any lot where a single family home is allowed. You can mix them any way you want. Two attached, two detached, or one of each. There is no minimum lot size for an ADU beyond what your zone already requires for the house.

Kenmore also allows middle housing, such as duplexes, triplexes and townhouses, in its R4 and R6 zones, with exceptions for lots next to streams and rivers. That is a different path with different rules. If you are weighing an ADU against a bigger project on your lot, it is worth asking about both.

Size Limits

Size depends on whether the unit is attached or detached, and on your lot.

An attached ADU can be up to 1,000 square feet. The exception is a conversion. If you are turning an existing floor of your house into an ADU, such as a daylight basement, the unit can be the full size of that floor.

A detached ADU on a lot of 6,000 square feet or more can be 17 percent of the lot area, up to a cap of 1,500 square feet. On a 10,000 square foot lot, that is 1,500 square feet. On a 7,000 square foot lot, it is 1,190 square feet. On a lot under 6,000 square feet, the cap is 1,000 square feet. For reference, 1,000 square feet is enough for a two bedroom, one bath home, and 1,200 is enough for two bedrooms and two baths.

Height Limits

A detached ADU can be up to 35 feet tall. The code also limits the number of stories. You can build one story over a detached garage, or two stories if the unit sits at ground level. An attached ADU follows the height limit for your zone, which is 35 feet in most single family zones. In R6, buildings on slopes over 15 percent can go higher, so a sloped lot may have extra room.

Setbacks

A setback is the minimum distance between a building and your property line. Kenmore applies the main house standards to ADUs, so the setbacks are the same for an attached ADU and a detached one.

A garage, carport or fenced parking area needs a driveway at least 20 feet long between it and the street line, so a car can park in the driveway without hanging into the sidewalk. A detached ADU also has to keep a gap from your house. The city measures that gap, 5 feet, from eave to eave. If your lot touches a public alley, a detached ADU can sit right on the property line on the alley side.

The R4 and R6 rear setback of 20 feet matters. On a narrow backyard, 20 feet from the back line plus 5 feet from the house can squeeze the space for a detached unit fast. A survey tells you what really fits.

If you are converting an existing structure, such as a garage, it can become an ADU even if it sits closer to the line than today's rules allow, as long as it meets the building code for living space. State law backs this up.

Owner Occupancy

Kenmore does not require you to live on the property. The old rule that the owner had to live in one of the units for six months a year is gone, and state law now bans it. You do not have to live on site to build or rent an ADU.

Parking

No off street parking is required for an ADU. You can still build a space if you want one.

Renting or Selling

You can rent your ADU, and you do not have to live next door. Kenmore also lets you sell an ADU separately from the main house, including as a condominium, which many Eastside cities still do not. The code limits the number of people who can live in each unit to the same limit that applies to any single family home. Kenmore's ADU section does not address short term rentals, so if nightly rentals are part of your plan, ask the city directly before you count on them. Check your plat and any homeowner association covenants too.

Fees

Kenmore is easier on fees than most cities. Here is what the published rules say.

• Impact fees. An impact fee is a one time charge that helps a city pay for roads, parks and schools as it grows. Kenmore's impact fee code exempts ADUs from all of them. If the unit is later converted to another use, fees apply at the rates in effect then.
• Building permit fee. The City Council waived it for new ADUs in 2023. The city's 2026 fee schedule also says its Development Services fees do not apply to new ADUs, and the stormwater capital facilities charge does not apply to the new hard surface for an ADU.
• Address assignment. The 2026 schedule lists $128 for a residential address. Confirm that is the ADU rate.
• Tree removal permit. About $50 for a tree 6 inches across or larger.

The waiver covers the building permit. Ask the city exactly which other lines it covers, such as plumbing, mechanical and electrical permits, before you set your budget.

The larger costs come from utilities. King County charges a sewer capacity charge on every new ADU, $46.01 a month in 2026 for 15 years, about $8,300 in total. Your water and sewer utility may add its own connection charges, and the power company will quote any new meter or panel work. The utility section below covers who to call.

How You Apply

Kenmore takes ADU applications online through MyBuildingPermit.com. The city's ADU page links to two checklists: #403 for a detached ADU and #407 for an attached ADU. Use those. An older ADU checklist, #220 from 2021, is still online and shows rules that no longer apply.

• A new detached ADU, or an addition that becomes an ADU, needs a site plan showing setbacks, the 5 foot gap from the house, hard surface totals and fire access, full floor plans and elevations, structural drawings, energy code documents and a stormwater submittal sized to the project.
• An ADU created inside your existing house, like a basement conversion, needs floor plans showing the existing and proposed layout, ceiling heights, egress windows and alarm locations. It is a lighter review.

One step catches people by surprise. Before the city approves the permit, you must record a notice with King County Records and Elections that identifies the unit as an accessory dwelling unit. The notice runs with the land, and you hand the city proof it was filed.

Do I Need to Hire an Architect?

No, not by law. Washington state does not require a licensed architect for homes with one to four units, and an ADU falls under that rule. Kenmore does not add an architect requirement of its own. A homeowner, a designer or a design build firm can prepare the drawings. You can read the state rule yourself at RCW 18.08.410.

That said, the drawings have to be right. Drawings that miss what the city asks for come back with comments, and every round of comments adds time. Some parts of the project do need a licensed professional. A geotechnical report must come from a licensed engineer. Structural calculations are needed for anything not sized from the prescriptive code tables. Stormwater features such as a rain garden need a letter from a qualified professional after they are built.

Watch for these

What Can Complicate Your Project

None of these usually kill a project. They change where the unit goes, what it costs, or how long it takes. Kenmore is generous on parking, fees and ownership. Its tough spots are trees, sensitive areas and drainage. The sooner you know which ones apply to your lot, the fewer surprises you get later.

Hard Surface: The Math That Decides How Much You Can Build

Kenmore has no separate lot coverage cap in its single family zones. The one lot limit is hard surface, which the code calls impervious surface. Hard surface is everything on your lot that rain cannot soak through: roofs, driveways, walkways, patios and decks. In R6, the base limit is 60 percent of the lot, and the city can approve up to 70 percent when you use low impact design, such as a rain garden. In R4 it is 45 percent, up to 55 percent. In R1 it is 30 percent. Lots under 9,076 square feet in R4 follow the R6 standard. Here is how the math works.

In that example, a 750 square foot cottage with a short path fits with room to spare. Many Kenmore R6 lots are in this position. A basement or garage conversion adds no new hard surface at all.

County records are often fuzzy about your existing footprint. They may not show the driveway, the patio or the true outline of the house. The city keeps its own yearly measurement of hard surface on each parcel, which is a better starting point, but a real site plan or survey is what settles it.

Trees and Roots

Kenmore cares a lot about trees, and this is where many Kenmore projects slow down. You need a tree permit to remove any tree 6 inches across or larger. A standard permit costs about $50 and takes about two weeks to review. Exceptional trees get much tougher treatment. These include any tree over 48 inches across, and large Douglas firs, western hemlocks and western red cedars at smaller sizes. An exceptional tree permit costs far more, can take months, and the penalties for removing a protected tree without one are steep. Trees inside a stream or wetland buffer can only be removed if they are hazardous.

The state ADU law says a city cannot hold an ADU to stricter tree retention rules than it applies to the main house, but Kenmore's tree permit still applies to any tree you want to remove. Roots also matter even when the tree stays. Heavy roots can decide where a foundation, a trench for utilities or a driveway can go. Walk your lot and note anything large before you fall in love with a location.

Streams, Wetlands and Slopes: Critical Areas

Critical areas are places the city treats as sensitive: streams, wetlands, steep slopes and unstable soil. Kenmore sits on the north end of Lake Washington, with Swamp Creek and several smaller streams running through it, so many lots have one nearby. Each critical area comes with a buffer, which is a no build zone around it. The city's critical areas code is KMC Chapter 18.55.

A critical area changes the plan in two ways. First, the buffer takes ground you cannot build on. Second, the state rules that make ADUs easier to permit do not apply to lots with mapped critical areas or buffers, so the city can apply stricter rules. A stream you have never noticed at the back of your lot can decide where the unit goes.

If your lot has a landslide or erosion hazard, plan for a geotechnical report. A geotechnical report is a soil and slope study done by a licensed engineer. It tells the city whether the ground can safely hold a new building. The city's map layers show most hazards before you spend a dollar, but they are a screening tool, not an assessment. A site visit can find a condition the maps miss. Kenmore does not publish a list of approved firms or a typical turnaround, so get schedules from local firms before you commit to a start date.

Stormwater and Drainage

Stormwater is rain that runs off roofs and paving instead of soaking into the ground. Kenmore follows the 2021 King County Surface Water Design Manual with its own addendum. The size of the new hard surface decides how much review you get.

Many ADUs add somewhere around 750 to 1,000 square feet of new hard surface, which lands in the middle row. Kenmore is a conservation flow control area and a basic water quality area, so the city expects the project to manage its own runoff on site. If you use a rain garden or other low impact feature, a qualified professional has to inspect it and send the city a letter. A bigger unit with a new driveway or a long walkway can cross the 2,000 line. A real site plan with the driveway and walkways drawn in is how you know for sure.

Fire Access and Sprinklers

Kenmore's fire code looks at how close a fire truck can get. The city uses a 150 foot walking distance rule, so a hose crew should be able to reach every part of a new home from the nearest place a truck can park. On a deep lot, or one with a long private driveway, a backyard cottage can fall outside that distance. The usual fix is a fire sprinkler system or a wider access path.

Whether your ADU needs sprinklers depends on the unit, the lot and how the city's fire code amendments apply to it. Ask the city's fire reviewer early, because the answer can change the investment in the project by thousands of dollars.

Fire Separation for Attached Units

Once part of your house becomes its own legal home, the two units need a fire rated wall and floor between them. A fire rated assembly is built with materials that slow a fire down, so a fire in one unit cannot spread fast into the other. Any door between the two units has to be a fire rated, self closing door. For a basement ADU, that usually means upgrading the ceiling between the basement and the main floor.

Egress and Basement Conversions

Egress means a safe way out in an emergency. Every bedroom in an ADU needs its own emergency escape window, and the unit needs a clear path to an outside door. In a basement, that often means cutting a larger opening into the foundation and digging a window well outside. This is real construction work, not paperwork.

Basement conversions have a few other checks too:

• Ceiling height. The space needs at least 6 feet 8 inches of ceiling height in habitable rooms. Measure it before you plan anything else.
• A full kitchen. A kitchenette with a sink and a fridge does not count. A legal ADU kitchen needs a permanent cooking appliance, plus the gas or electrical work to run it.
• The separate entrance. A walkout or outdoor stairway still has to be checked against your foundation and your drainage.

Water, Sewer, Power and Other Utilities

• Water and sewer. Most Kenmore homes are served by Northshore Utility District. Start with a water and sewer availability letter, which costs $135 and takes about 2 to 4 weeks. The district decides whether your ADU can share the existing water service and side sewer or needs its own, and whether its connection charges apply. Get that answer in writing before you budget.
• King County sewer capacity charge. $46.01 a month in 2026 for 15 years, about $8,300 in total, for an ADU that connects to sewer.
• Power. Puget Sound Energy publishes no standard fee for a residential service. Ask for a quote on a new meter or a subpanel feed from your house.
• Gas. Only if you want it. Puget Sound Energy gives a custom estimate and 6 to 12 weeks is typical. Confirm there is a gas main on your street.
• Address assignment. The new unit needs its own address, $128, before the city moves forward on the permit.
• Pre approved plans. Ask the city whether it has a pre approved ADU plan program. Do not assume it does.

Timeline

How Long Does a Kenmore ADU Permit Take?

Kenmore does not publish a review target for ADU permits. The city's Development Services line is 425-398-8900, and questions about fees and process can go to permittech@kenmorewa.gov. They can give you the current estimate. What you can control is the list of things that have to happen before the city accepts your application, and those are where most timelines slip.

Most projects go through more than one round of city comments. A clean, complete first submittal is the single best way to keep that number low.

Here is the order things happen in, and where the delays come from.

1. Jurisdiction and zone check. Confirm the parcel is inside Kenmore city limits, which zone it carries, and who provides water and sewer.
2. Lot review. Your property lines, hard surfaces, slopes, streams and large trees get measured on the ground, not pulled from records. The hard surface total gets built here.
3. Design. Unit sizes and locations get tested against the setbacks, the 5 foot gap from the house, the hard surface cap, the trees and your yard. You should see options before anything is drawn for the city.
4. Reports, if required. A geotechnical report on lots with a mapped hazard. A tree plan if protected trees are involved. Neither has a published turnaround, so get real schedules from local firms before you commit to a date.
5. Address, utility and notice items. These run in parallel with design. The utility letter is the one to start earliest.
6. Permit submittal. The application goes in online through MyBuildingPermit.com with the site plan, floor plans, elevations, structural and energy documents, the stormwater submittal and the items above.
7. City review. The city reviews the plans and sends comments. The design team answers them and resubmits as needed.
8. Permit issued. Remaining permit fees are paid, and construction can start.

The biggest swing factors in Kenmore are trees and critical areas. A flat lot with no protected trees and plenty of room under the hard surface cap can move fast, because there are no parking, owner or impact fee issues to work through. A lot with a stream, a slope or a large Douglas fir in the way may wait on a redesign, a tree permit or a soil report before the drawings can be locked. Settling those early is the best way to keep your timeline from slipping.