Shoreline ADU Permit Requirements, in Plain English

The short answer

Can I Build an ADU in Shoreline?

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. 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 to it.

Shoreline rewrote its zoning in early 2025. The City Council adopted the new code on January 13, 2025 with Ordinance 1027, along with a new zoning map. The old rules are gone. Under the old code, a lot could have only one ADU, the unit could not be larger than half the living area of the house, one extra parking space was required, and the owner had to live on site. If you read about Shoreline ADUs more than a year or two ago, or you find an older city handout, a lot of what you read no longer applies.

Today 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 Shoreline Is Your Permit City

A Shoreline mailing address does not always mean the City of Shoreline holds your permit. The 98133, 98155 and 98177 ZIP codes are shared with Seattle, Lake Forest Park and nearby areas, and each of those has its own ADU rules.

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

Know Your Zone

Most of Shoreline's old R4 and R6 single family neighborhoods became Neighborhood Residential 3, called NR3, or Neighborhood Residential 2, called NR2. NR3 is the lower density zone, built around lots of 7,200 square feet. NR2 is denser and sits closer to busy streets and shopping areas. A third zone, NR1, covers the highest density areas. The ADU rules on this page apply wherever a home is allowed, but the setbacks, height and hardscape limits depend on your zone, so find yours before you design. Your plat and any homeowner association covenants can add limits on top of the city's.

Confirmed rules

Shoreline ADU Rules: What Is Confirmed

Zoning and How Many Units You Can Build

Shoreline allows up to two ADUs on a residential lot. You can mix them any way you want. Two attached, two detached, or one of each.

The part that surprises people is the count. In Shoreline, ADUs count toward the total number of homes your zone allows on a lot. That total is generous. NR3 allows at least three homes on any lot, and four within a half mile of a major transit stop. NR2 allows at least four. A house plus two ADUs is three homes, so it fits in either zone. The city also now allows duplexes, triplexes, townhouses and other middle housing in these zones. 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

The maximum size for an ADU is 1,200 square feet, attached or detached. For reference, 1,000 square feet is enough for a two bedroom, one bath home, and 1,200 is enough for a comfortable three bedroom.

There is one exception. An ADU inside your house that sits on its own floor and shares the same roof, such as a daylight basement, is not held to the 1,200 square foot cap. If you are converting a full lower floor, the unit can use all of it.

Height Limits

Shoreline does not set a separate height number for ADUs that we could find in the code. A detached ADU follows the base height for your zone. In NR3 that is 23 feet, or 28 feet with a pitched roof. In NR2 it is 30 feet, or 35 feet with a pitched roof. State law also bars a city from limiting an ADU roof height to less than 24 feet, or to less than the height of the main house if that is lower. Ask the city which number it will apply to a detached unit on your lot before you lock the design.

Setbacks

A setback is the minimum distance between a building and your property line. In both NR3 and NR2, the standards are the same.

If your lot touches an alley, a detached ADU can sit right on the side or rear property line on the alley side. Some arterial streets and the corridors around the light rail stations carry different front setbacks, so check your street.

The 10 foot rear setback matters. On a shallow backyard, 10 feet from the back line plus the distance the building code asks you to keep from your house can squeeze the space for a detached unit fast. A survey tells you what really fits.

Shoreline's older ADU handout said a nonconforming garage or shed, one that sits closer to the line than today's rules allow, could not be turned into an ADU. State law now protects the conversion of existing structures in many cases, but we could not confirm how Shoreline applies it. If a garage conversion is your plan, ask the city in writing.

Owner Occupancy

Shoreline does not require you to live on the property. The old rule that the owner or a close family member had to live in one of the units is gone, and Washington state law bars cities from requiring it. The city's current ADU handout lists no owner occupancy rule. Older city documents and many websites still show the old rule, so do not rely on them.

Parking

Shoreline asks for one extra off street parking space for an ADU. There is a big exception. No parking is required when your property is within a half mile of a major or frequent transit stop, and the city can also waive parking when your property is near transit and has on street parking out front. Much of Shoreline sits inside that distance, especially near the light rail stations and the busy bus lines. Standard spaces are 8 feet by 20 feet, and up to half of a property's spaces can be compact at 8 feet by 16 feet. Check your address on the city's map or ask the Permit Center.

Renting or Selling

You can rent your ADU, and you do not have to live next door. State law lets cities regulate short term rentals, and we found nothing in Shoreline's ADU rules that addresses them, so if nightly rentals are part of your plan, ask the city directly before you count on them. State law also lets an ADU be sold separately as a condominium. Shoreline's older code barred selling an ADU apart from the house, so confirm how the city handles a sale before you plan around it. Check your plat and any homeowner association covenants too.

Fees

Shoreline charges less for ADUs than for a new house, but not nothing. 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 fire service as it grows. Shoreline charges transportation, park and fire impact fees on new homes, including ADUs, at reduced amounts. State law caps ADU impact fees at half the fee for the main house. For the park fee, the city charges the lesser of half the main house fee or a rate based on the ADU's square footage. The fees are due after the city finishes reviewing your building permit and before the permit is issued.
• Building permit and review fees. A building permit is required for every ADU, along with plumbing, mechanical and electrical permits where the work calls for them. The city's fee schedule sets the amounts, which depend on the value of the work.
• Tree fees. A per tree fee applies to significant trees 24 inches across or larger. The tree section below covers when a permit is needed.

The exact impact fee for your unit depends on its size and the rates in effect when you apply. Ask the Permit Center for a written estimate, or use the city's fee page, before you set your budget.

The larger costs often come from utilities. Your water provider, the city's wastewater utility and the power company each have their own connection rules and charges. The utility section below covers who to call.

How You Apply

Shoreline takes building permit applications online through MyBuildingPermit.com. The city's permit pages list the submittal checklists for each permit type. Use the current ones, because older ADU handouts and checklists online show rules that no longer apply. Your plans have to show how the unit meets zoning, building, fire and other codes, and the site plan must show every existing and new building, parking, driveways, setbacks, hardscape and height.

• A new detached ADU, or an addition that becomes an ADU, needs a site plan drawn to scale, full floor plans and elevations, structural drawings, energy code documents and a drainage 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.

Shoreline has no pre approved ADU plans, so most homeowners hire a designer or a design build firm. The city also lets you book time with a planner to talk through a project before you apply. Reach the Planning and Community Development team at 206-801-2500 or pcd@shorelinewa.gov.

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. Shoreline 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. Drainage designs for larger projects need an engineer.

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. Shoreline is generous on owner rules and frontage work, and it can be flexible on parking. Its tough spots are hardscape, trees and sensitive areas. The sooner you know which ones apply to your lot, the fewer surprises you get later.

Hardscape: The Math That Decides How Much You Can Build

Shoreline limits how much of your lot can be covered by hardscape. Hardscape is everything on your lot that rain cannot soak through, and in Shoreline that includes buildings as well as paving: the house, garage, new ADU, driveway, walkways, patios and gravel. The base limit is 50 percent of the lot. Once your lot has two or more homes, which an ADU makes true, NR2 lots can go up to 60 percent. NR3 lots stay at 50 percent. Here is how the math works.

In that example, a 750 square foot cottage with a short path fits with room to spare. A 1,200 square foot unit with a new parking pad would be tight. A basement or garage conversion adds no new hardscape at all. This is also where the parking exception pays off. If your property is close enough to transit that no parking is required, you do not have to pave a space just to meet a rule.

County records are often fuzzy about your existing footprint. They may not show the driveway, the patio or the true outline of the house. A real site plan or survey is what settles it.

Trees and Roots

Shoreline treats trees seriously, and this is where many projects slow down. The city calls any tree 6 inches across or larger, measured 4.5 feet above the ground, a significant tree. The rules are simple to state and harder to live with.

• Retention. At least 35 percent of the significant trees on a property must be kept. On a site with a critical area or its buffer, the number is 30 percent.
• Permit. A permit is required to remove a significant tree. Trees under 6 inches can come out without one, unless they sit in a critical area or buffer or the work clears more than 1,500 square feet.
• The removal allowance. You can remove trees up to 24 inches across without permit review, retention or replacement, within any 36 month period. The limit is 3 trees on a lot up to 7,200 square feet, plus 1 more for each additional 7,200 square feet. You still have to tell the city. The allowance does not apply inside critical areas.
• Replacement. Removed trees must be replaced. A tree 6 to 8.9 inches across needs 1 replacement. A tree 9 to 11.9 inches needs 2. A tree 12 inches or larger needs 3.
• Large trees. A per tree fee applies to significant trees 24 inches across or larger, and the fines for removing a protected tree without a permit are steep, up to $15,000 for a tree that size.

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

Streams, Slopes and the Puget Sound Shoreline: Critical Areas

Critical areas are places the city treats as sensitive: streams, wetlands, steep slopes and unstable soil. Shoreline has several creeks, including Boeing Creek and Thornton Creek, and steep bluffs along Puget Sound. Each critical area comes with a buffer, which is a no build zone around it. The city's critical areas code is SMC Chapter 20.80.

A critical area changes the plan in a few ways. The buffer takes ground you cannot build on. The tree retention number drops to 30 percent and the removal allowance goes away. And the state rules that make ADUs easier to permit do not reach lots with mapped critical areas or buffers, so the city can apply stricter rules there. A stream you have never noticed at the back of your lot can decide where the unit goes.

Lots near Puget Sound, such as parts of Richmond Beach and Innis Arden, can also fall under the city's Shoreline Master Program, which adds its own review for work close to the water. 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. Shoreline does not publish a typical turnaround for these reports, 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. Shoreline reviews how a project handles it, and the amount of new hard surface decides how much review you get. A small addition usually gets a simpler review. A larger unit with a new driveway or a long walkway can trigger a full drainage design by an engineer. The city's drainage thresholds sit in its engineering standards, so ask the Permit Center which tier your plan lands in. A real site plan with the driveway and walkways drawn in is how you know for sure.

Fire Access and Sprinklers

Shoreline's building and fire codes look at how a home is protected from fire. For ADUs, the city's handout says a detached ADU needs to meet fire separation standards and have fire sprinklers. An attached ADU needs a fire wall between the units, or hardwired smoke alarms together with fire sprinklers. Sprinklers are real construction work and add to the investment in the project, so find out early which path applies to your unit. Ask the city's fire reviewer if you are unsure.

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, unless you take the alarm and sprinkler path above. 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

Each unit also needs unrestricted access to its own utility shutoffs for water, electricity and fuel gas, either inside the unit or in a shared area. Plan where the meters and panels go early.

• Water. Two providers serve Shoreline. Seattle Public Utilities serves the part of the city generally west of Interstate 5, and North City Water District serves the part generally east of it. Ask your provider for a water availability and fire flow certificate, which shows the distance to the nearest hydrant and the flow rate. Seattle Public Utilities is at 206-684-5800 and North City Water District is at 206-362-8100. Ask each whether your ADU can share the existing water service or needs its own, and what connection charges apply.
• Sewer. The City of Shoreline took over the Ronald Wastewater District in 2021 and now runs sewer service for most of the city. The Highlands Sewer District serves a small part of the Highlands neighborhood, and a few lots still use septic systems. Ask your sewer provider whether your ADU can share the existing side sewer and whether any capacity or connection charge applies.
• Power. Seattle City Light serves most of Shoreline. Ask for a quote on a new meter or a subpanel feed from your house.
• Gas. Only if you want it. Puget Sound Energy provides gas service. Confirm there is a gas main on your street.
• Pre approved plans. Shoreline does not have a pre approved ADU plan program. Plan on a custom set of drawings.

Timeline

How Long Does a Shoreline ADU Permit Take?

Shoreline posts typical permit review times on its permit information page, and the Permit Center can give you a current estimate for an ADU. 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 Shoreline city limits, which zone it carries, and who provides your water and sewer.
2. Lot review. Your property lines, hardscape, slopes, streams and large trees get measured on the ground, not pulled from records. The hardscape total gets built here.
3. Design. Unit sizes and locations get tested against the setbacks, the hardscape 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 significant trees are involved. Neither has a published turnaround, so get real schedules from local firms before you commit to a date.
5. Utility items. These run in parallel with design. The water certificate 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 drainage 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. Impact fees and permit issued. The impact fees and remaining permit fees are paid, the permit is issued, and construction can start.

The biggest swing factors in Shoreline are trees, critical areas and the hardscape math. A flat lot with no large trees and plenty of room under the hardscape cap can move fast, because there are no owner rules or frontage work to deal with. 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.