Search for shoreline rules near Seattle and you may find two very different topics. One is the City of Shoreline, a separate city just north of Seattle with its own code. The other is a set of environmental rules for land near lakes and the Sound. This guide focuses on Shoreline ADU regulations, meaning the rules of the City of Shoreline, and explains how to keep the two topics apart.

It covers permits, unit counts, size, parking, frontage, fire safety and impact fees. The details reflect official City of Shoreline sources checked in October 2026. Because codes change, confirm every point with the city before you design.

The City of Shoreline Versus Shoreline Environmental Rules

The City of Shoreline runs its own permit office and adopts its own development code. So a lot inside Shoreline city limits follows Shoreline rules, not Seattle rules. For that reason, a Seattle checklist will not tell you what Shoreline requires. Also, a Seattle mailing address does not always match city limits, so check the parcel itself.

Seattle, by contrast, has a Shoreline Master Program that regulates development in the city’s shoreline environments. According to SDCI, development in Seattle’s Shoreline District needs a shoreline substantial development permit or a shoreline exemption. That program applies to waterfront areas inside Seattle and has nothing to do with the separate City of Shoreline.

Where Shoreline ADU Regulations Are Written

The City of Shoreline regulates ADUs in SMC 20.40.210 of its Development Code. Note that this SMC means the Shoreline Municipal Code, not the Seattle Municipal Code. The city also publishes a short ADU handout with plain summaries.

The handout reminds readers that it does not replace the code. Therefore, use it as a starting point and read the code section for exact wording. If the two ever seem to differ, ask city staff which text controls. In addition, state law under RCW 36.70A.681 sets minimum ADU standards for many Washington cities.

Permits and Plans

According to the handout, every ADU in Shoreline needs a Building Permit, including internal remodels and new buildings. In addition, plans must show how the unit meets zoning, building, fire and other code requirements. The city points applicants to its permit applications webpage for checklists and required documents.

The handout also says Shoreline does not offer pre-approved ADU plans like some other cities. As a result, many owners hire a design professional. Seattle runs a different program, as our article on how Seattle preapproved DADU plans work explains.

Unit Count and Size Under Shoreline ADU Regulations

Shoreline’s code allows two ADUs per lot, subject to the city’s maximum density calculations. The handout explains that ADUs count toward the maximum number of houses on a lot. Also, an ADU may sit inside the main structure or in a detached building.

The code caps an ADU at 1,200 square feet. However, an interior unit may exceed that limit when it sits on a separate floor and shares a common roof with the main home, such as a basement unit. For a Seattle comparison, see our guide on whether a property can have two accessory dwellings.

Parking and Frontage Improvements

The handout states that Shoreline requires no off-street parking for an ADU. If you choose to provide parking, it must meet the city’s spacing and design standards. Spaces also need clear access, so one car does not block another.

Frontage improvements include curb, gutter, sidewalk and street trees along the street edge of a lot. According to the handout, you do not have to build frontage improvements when you add an ADU. That can make a real difference for budget planning, since street work can add cost and time. Our article on what parking rules mean for ADU projects covers Seattle’s approach.

Fire Safety and Building Code Points

The handout says an ADU must meet applicable Shoreline building codes. For example, detached ADUs need to meet fire separation standards and have fire sprinklers. Similarly, attached units need a fire wall or hard wired smoke alarms and fire sprinklers.

Every unit also needs unrestricted access to its own utility controls for water, electricity and fuel gas, either in the home or in a common area. Because these points affect layout, share them with your designer at the start. That way, the first draft of the plan already reflects them.

Fees and Impact Fees

First, building permits in Shoreline carry permit fees based on the city’s fee schedule. The city also charges transportation, park and fire impact fees on new homes, and the handout notes that ADUs have reduced fee amounts. According to the handout, owners pay impact fees after review ends but before the city issues the permit.

We do not list fee amounts here, since they change. Instead, check the city’s current fee pages or ask staff for an estimate based on your plans. That way, your budget rests on current numbers.

Next Steps With Shoreline ADU Regulations

First, confirm that your parcel lies inside Shoreline city limits rather than Seattle or unincorporated King County. Next, read the handout and SMC 20.40.210, then list your questions. Then include site features such as slopes, trees and existing structures. Keep the list short and clear so staff can answer it quickly.

Finally, contact the city’s Planning and Community Development team before you design. With the right city, the right code and clear answers, Shoreline ADU regulations become a manageable part of planning. In the end, a little research up front can spare you redesign later.