Seattle ADU Design and Permits

The governing authority depends on the property. City of Seattle applications use City processes. Other incorporated cities and unincorporated King County maintain their own guidance and portals. Establish jurisdiction before selecting a plan provider or permit strategy.

What happens before drawings?

Complete enough feasibility work to identify the legal parcel, existing development, proposed ADU type, available envelope, access, utilities and known overlays. Decide who obtains missing survey, structural, geotechnical, arborist, fire, historic or other specialist information.

The design brief should state room/size goals, intended use, privacy, accessibility priorities, finish level, budget and items the owner will supply.

What may the drawing package contain?

Project requirements vary, but a complete package commonly draws from:

• cover sheet, scope and code information;
• existing and proposed site plans;
• area and zoning calculations;
• floor and roof plans;
• exterior elevations and building sections;
• door/window and finish information;
• foundation and framing plans/details;
• structural calculations where required;
• mechanical, electrical and plumbing information;
• Washington State Energy Code forms and supporting documents;
• drainage, grading or civil information where required; and
• manufacturer or deferred-submittal documents.

SDCI’s ADU guidance links code resources, permit paths and standard-plan instructions. Individual projects may require fewer or additional documents depending on the property and work.

Who owns and coordinates the design?

Ask for the legal name and role of the architect, engineer, designer, energy consultant, surveyor and permit representative. State whether the construction provider employs them, subcontracts them or expects the owner to contract separately.

The agreement should identify:

• number of concepts and revision rounds;
• who owns/reuses the drawings;
• site visits and measurements;
• consultant fees;
• agency submission and response responsibility;
• redesign triggered by budget or site information;
• construction-phase questions and revisions; and
• what happens if the construction contract is awarded elsewhere.

What does pre-approved mean?

SDCI says ADUniverse pre-approved DADU plans have completed recurring structural and energy review, while the property still needs site-specific zoning, foundation, drainage, utility and other review. Kirkland and Renton operate separate local plan programs; Bellevue says its program is still under development. Check every plan claim against the governing city’s live program.

See standard plans versus custom ADUs.

Plan review is an exchange, not one date

A schedule should identify initial submission, completeness, agency review, correction issuance, consultant response, resubmission, other clearances, permit issuance and conditions before work begins.

Ask the provider to distinguish:

• statutory or agency review periods;
• its own response time;
• time waiting for owner decisions;
• utility or outside-agency work; and
• total calendar duration.

Do not convert a review target into a guaranteed permit date.

How are permit and consultant costs handled?

Separate fixed design fees, consultant estimates, agency fees, utility charges and reimbursable expenses. Mark which values are known, allowances or paid directly by the owner.

If a design-build company advertises one total, ask what happens when plan review requires structural, utility or site changes. The cost guide provides the categories.

What should be complete before construction pricing?

Pricing can begin earlier as a planning exercise, but a firm comparison needs a stable site plan, floor area, structural basis, finish schedule, utility assumptions and external-work scope. Every bidder should receive the same revision.

Require an addendum log when drawings change. A provider should confirm which dated set its price uses.

Permit responsibility belongs in writing

Washington L&I advises homeowners to use a written contract and understand the work and payment terms. The project agreement should also state who obtains permits, attends inspections, answers corrections, supplies deferred documents, pays reinspection charges caused by its work and obtains closeout records.

Use the builder comparison to record these responsibilities.

Control revisions after submission

Keep a drawing register with the sheet date, revision description and recipient. When an owner, agency or field condition changes the design, identify which architectural, structural, energy and building-system sheets are affected before work proceeds.

A proposal should state how ordinary correction responses are included and how owner changes are priced. It should also identify who checks that the construction team is using the current approved set. These controls belong in the complete ADU budget, because a low design fee can become expensive when coordination and revisions are excluded.

Require written distribution of each approved revision to the owner, site supervisor and affected trades.

What should the owner receive at permit issuance?

Permit issuance should produce a usable construction file, not only an approval notice. Ask for the stamped or issued drawing set, permit conditions, approved product or deferred-submittal lists, inspection sequence, correction history and any utility or outside-agency approvals that remain open. Record the permit number and expiry or renewal conditions.

Before signing the construction agreement, compare that issued file with the priced set. Resolve any change in floor area, structure, equipment, finishes or site work in writing. This check prevents a bidder from pricing an older concept while the field team builds from a later permit set.