Many owners first meet backyard cottages through a gallery of ready made designs. The appeal is clear, since part of the work already looks done. A Seattle preapproved DADU plan does shorten some steps, but it does not replace every review.

This guide explains what the city has already checked, what it still checks on your lot and what you still need to submit. It also clears up a common mix up about plans you can buy online.

What a Seattle Preapproved DADU Plan Is

Seattle uses the term standard plan for a set of construction plans that the city has approved ahead of time. According to SDCI, these plans comply with the building and energy codes and suit use on more than one site. The city’s preapproved cottage designs follow this standard plan process.

The designs appear on ADUniverse, the city’s accessory dwelling unit website. Each one has a standard plan number, and the application must reference that number.

What the City Already Reviewed

The city reviewed the cottage structure itself before it added each design to the gallery. That review covered the Land Use Code, the Residential Code and the Energy Code for the building.

As a result, SDCI lists several benefits. You know the construction requirements before you apply, permit fees drop and plan review runs faster. Our guide to Seattle ADU permit fees explains how fees add up in general.

Site Checks Every Project Still Needs

A plan cannot know your lot. So SDCI still checks that the plan set matches the standard plan on file. Then it reviews site factors, such as zoning fit, foundation design, utility design and drainage.

Electrical permits also stay site specific. In addition, protected trees or critical areas on a site can add review and time. Our guides on DADU lot eligibility and Seattle DADU trees cover those early site questions.

Who Can Use a Seattle Preapproved DADU Plan

The city’s current help article sets clear limits for the preapproved path. You can use it only when the project meets each of these terms.

• Zone. The lot sits in a Neighborhood Residential zone.
• Critical areas. No environmentally critical areas affect the site.
• Ground disturbance. Earth work stays under the city’s limit.
• Design. You use one of the designs on ADUniverse and cite its plan number.
• Completeness. Your package is ready for review.

If your lot does not meet these terms, you may still build a similar cottage. However, it would follow the regular review path instead.

Ground disturbance often decides the question. For example, a long new sewer trench or a deep foundation on a slope can move more soil than the program allows. So ask your designer to estimate earth work early, before you commit to a design.

Design Ownership and Licensing

The city does not own these designs. When it launched the program, the city stated that designers retain ownership of their plans. To use one, a homeowner pays the designer a royalty and connects with the designer to move forward.

Owners then have choices. For example, they can hire the original designer to prepare the site plan or help with the permit. Otherwise, the designer can ask the owner to sign a liability release before using the plan with other professionals. Our post on DADU design cost explains why site work still needs design time.

Limits on Changing a Seattle Preapproved DADU

The value of a standard plan comes from its sameness. Each later application must use a plan set identical to the one on file. SDCI asks applicants to mark the options they use and strike through the rest.

Options exist, but only within limits. A designer can include reversals, alternate roof lines and similar choices without big structural changes. A larger change means the plan no longer matches, so the project would likely need a regular review. Also, when the city adopts new building or energy codes, a standard plan needs a new approval.

What You Still Submit

A preapproved design still needs a full application. The city’s help article lists the uploads.

• Site plan with the legal description and parcel number
• Statement of Financial Responsibility form, if required
• Rat abatement declaration when you remove an accessory structure
• King County capacity charge form
• Plan set that shows existing buildings, the new cottage, a pedestrian path and the approved standard plans

You can read the full steps in the city’s guide on applying with a preapproved standard plan.

Why Commercial Plans Differ From City Plans

Many companies sell cottage plans online, and some call them predesigned or ready to build. That label does not mean the city has reviewed them. Only designs in the city program carry a standard plan number.

A purchased plan can still work well, and many owners use them as a starting point. Even so, it goes through the regular review like any custom design, and it may need changes to meet local codes. So ask any seller whether the plan holds a Seattle standard plan number.

Before you choose, compare a few gallery designs with your lot survey. Check the footprint against setbacks and the height against the limit for your zone. That quick test shows whether a design fits before you pay for it.

Overall, a Seattle preapproved DADU plan removes some review of the building, but your lot still needs its own checks. The current city help pages remain the best guide to each step.