If you are serious about building a backyard cottage in Seattle, pre-approved standard plans are one of the smartest places to start your research. Seattle's Department of Construction and Inspections says these plans can offer a faster, easier, and more predictable permitting process, and that many eligible projects can receive permits in about two to six weeks. That is dramatically different from a fully custom path that can involve more site-specific drawing work, more correction cycles, and more consultant coordination.
But there is a catch that most homeowners miss:
Pre-approved does not mean automatically buildable on your property. Seattle has pre-reviewed the building package — not your setbacks, trees, utilities, drainage, or lot geometry.
Seattle still requires a site plan, parcel information, a pedestrian path from the right-of-way, sewer paperwork, and full compliance with current code. Seattle Public Utilities may still require a Water, Drainage, and Wastewater Availability Certificate. Stormwater review can still trigger. Trees can still block or reshape your preferred footprint. Side-sewer work still has to be permitted through SPU.
That is exactly why a homeowner should evaluate lot readiness before buying a plan license — not after.
The $55 Seattle DADU Pro Guide helps you check setbacks, trees, utilities, drainage, and access first — so you do not license a plan your lot cannot support.
How Seattle's expedited standard plan path works
Seattle's Services Portal guidance (updated May 14, 2026) confirms the expedited standard-plan path is active for DADU projects that meet four conditions:
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Use a pre-approved DADU plan from the ADUniverse gallery
The application must include the specific standard-plan number. Seattle has pre-reviewed these plans for code compliance, which compresses design review time significantly.
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Build on an eligible Neighborhood Residential lot
A practical note: Seattle's One Seattle implementation made permanent Neighborhood Residential changes effective January 21, 2026, but the DADU portal article updated in May 2026 still uses the older NR-1/NR-2/NR-3 terminology. Verify current lot eligibility against the latest city guidance at the time of your application — the program appears live, but the portal language may lag the newest zoning nomenclature.
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No environmentally critical areas on the property
If your lot has any mapped ECA condition — steep slopes, landslide hazard, wetlands, peat settlement, or shoreline overlay — the expedited path is not available under current portal guidance. The project reverts to standard review.
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Keep total ground disturbance under 750 square feet
This is a stricter threshold than the general stormwater review trigger (750 sq ft of hard surface or building area). Staying under it is part of what qualifies the project for expedited review.
Even on the standard-plan path, homeowners must still upload: a site plan with legal description and parcel number, a pedestrian path from the right-of-way to the proposed DADU, sewer-capacity paperwork, and the standard-plan set. The design is pre-approved. The site is not.
The right order is: confirm the lot can work — then choose the best-fitting standard plan — then license the design. Most homeowners do this in reverse and pay for it.
Permit timeline: pre-approved vs. custom paths
The timelines below are based only on durations Seattle and SPU publicly state. The custom DADU review timeline is shown as variable because Seattle does not publish a universal duration for custom projects — it depends on corrections, consultants, and site complexity.
- 1Lot feasibility screen — zoning, trees, utilities, drainage, access
- 2WAC if triggered — SPU, typically ~15 business days, no charge
- 3Seattle Services Portal intake with standard-plan number + site documents
- 4City review — typically 2 to 6 weeks on eligible lots
- 5SPU side sewer permit — issued after construction permit
- 1Lot feasibility screen — zoning, trees, utilities, drainage, access
- 2WAC if triggered — SPU, typically ~15 business days, no charge
- 3Full custom plan set — architect, site-specific drawings, consultant coordination
- 4City review — variable; Seattle does not publish one universal duration
- 5SPU side sewer permit — issued after construction permit
Both paths require the same lot-readiness work at step one. That is the step the plan purchase cannot skip.
Current plan options to evaluate first
Seattle's ADUniverse gallery currently includes six named pre-approved designs from six architecture firms. All six are listed below with the specs published in the program.
Important: The City of Seattle does not make any representations or warranties regarding these construction plans, including their quality, safety, compliance with building codes or state or federal laws, or suitability for a homeowner's property. Homeowners using a pre-approved plan rely solely upon the designer, architect, or contractor for any representations, warranties, and assurances with respect to the DADU design and construction plans.
| Firm / Plan | Size | Bed / Bath |
|---|---|---|
| CAST Architecture — Cedar Cottage | 467 sq ft | 1–2 bed / 1 bath |
| Fivedot Architects — Schooner | 1,000 sq ft | 2 bed / 2 bath |
| Ahouse Studio — The Family | 808–964 sq ft | 2–3 bed / 2 bath |
| Haas Architectural — Two Story, One Story & Studio | 288 / 432 / 576 / 940 sq ft | Studio, 1 bed, 2 bed |
| Artisans Group — Seattle DADU | 600 sq ft | 1 bed / 1 bath |
| Mobile Office Architects — MOA Family ADU /// 16x26 | 850 sq ft | 2 bed / 1 bath |
Additional design submissions may be included in the live ADUniverse gallery. Verify current plan availability and full spec sheets directly with SDCI before making any design or permitting decision.
CAST Architecture — Cedar Cottage
At 467 square feet, the Cedar Cottage is a compact and efficient one- or two-bedroom, one-bath plan. CAST Architecture describes it as an extremely efficient footprint that provides well day-lit space for living and necessary storage. The plan offers flexibility on many sites, including sloped ones, covered outdoor porch space, and easy expandability for families or roommates as a two-bedroom model.
Fivedot Architects — Schooner
The Schooner is a 1,000-square-foot, two-bedroom, two-bath plan — the largest in the current pre-approved catalog and the maximum allowable DADU size under Seattle's code. Fivedot Architects describes it as a family-friendly, low-cost design that can house a family of four or more. The plan can be mirrored or rotated and is easily adaptable to sloping sites.
Ahouse Studio — The Family
The Family offers a flexible layout ranging from 808 to 964 square feet with two to three bedrooms and two baths. Ahouse Studio designed this two-story plan to fit up to three bedrooms and serve a variety of family sizes. It is just under the maximum allowable square footage for a backyard cottage in Seattle and may be built on lots starting at 30 feet wide.
Haas Architectural — Two Story, One Story & Studio
Haas Architectural offers the widest range of any plan family in the program: a studio at 288 square feet, a one-bedroom at 432 square feet, a two-bedroom at 576 square feet, and a two-story unit at 940 square feet. Each plan is adaptable to site conditions and is constructed from a "kit of parts" that allows homeowners to self-construct substantial portions of the project if desired.
Artisans Group — Seattle DADU
The Seattle DADU is a 600-square-foot, one-bedroom, one-bath plan designed for aging-in-place and energy efficiency. Artisans Group describes it as capable of being an accessible home, aesthetically flexible to work with varied neighborhood styles. Published specifications include gable or shed roof versions, insulated slab-on-grade foundation, three-foot-wide doorways, stairless entry option, and curbless shower option. For buyers prioritizing accessible design and a single-level rental footprint, this plan is a strong starting point to compare against your lot.
Mobile Office Architects — MOA Family ADU /// 16x26
The MOA Family ADU is an 850-square-foot, two-bedroom, one-bath plan. Mobile Office Architects describes it as inspired by the Swedish philosophy of lagom — living with just the right amount — offering a fully functioning family dwelling in a small package. The 16x26 footprint is a practical consideration when evaluating rear-yard clearance against your setback envelope.
The $55 Seattle DADU Pro Guide helps you check the conditions that actually kill DADU projects before you license a $1,000 plan set.
The checklist every homeowner should run before buying a pre-approved plan
Use this as your decision gate. If you cannot clear these questions, do not pay a designer yet.
- Is the parcel in a zone category Seattle currently accepts for the standard-plan path?
- Given the January 2026 NR zoning changes, have you verified eligibility against the newest city guidance rather than older NR-1/2/3 terminology?
- Can the project stay within the current portal workflow requirements?
- Does the plan footprint fit within the buildable area after applying front, side, and rear setbacks?
- Can you show a clear pedestrian path from the right-of-way to the DADU on a site plan?
- Does the existing house placement leave enough rear-yard space for the chosen plan?
- Has the property been checked for mapped ECA conditions (slopes, landslide, wetlands, peat, shoreline)?
- If any ECA is present, have you confirmed the expedited path is still available?
- Are there large trees near the build area? (Tier 1: heritage trees; Tier 2: 24"+ DSH; Tier 3: 12–24"; Tier 4: 6–12")
- Could any protected tree block the chosen plan footprint or utility routing?
- Is arborist review likely to be required?
- Has a Water, Drainage, and Wastewater Availability Certificate (WAC) been requested or reviewed? (SPU says WAC required for most development projects; typically ~15 business days, no charge.)
- Are electrical service changes or new services needed?
- Is the existing water line adequate?
- Has the side sewer been scoped for condition, capacity, and routing?
- Are you aware that as of October 1, 2025, SPU handles all sanitary/wastewater plan review and side-sewer permitting, and cannot issue a side sewer permit until the construction permit is issued?
- Are side-sewer legal documents likely to be required?
- Will total ground disturbance stay under 750 sq ft? (Required for expedited-path eligibility.)
- Will new hard surface (patios, walkways, driveway) stay under 750 sq ft? (General stormwater review trigger.)
- Is there a workable stormwater discharge path?
- Can equipment reach the build area via alley, wide side yard, or rear access?
- Is there room for material staging?
- SPU recommends calling 811 two business days before digging to locate utilities — is that factored into the schedule?
Why the Seattle DADU Pro Guide is the smarter first buy
A pre-approved plan is appealing because it compresses design risk. It does not compress lot risk. And lot risk is where Seattle homeowners burn money.
Consider the stack: one current documented plan sells for $1,000 to Seattle residents before any site-specific work begins. Typical Seattle DADU construction costs commonly run $300,000 to $500,000 or more depending on design, size, and finish level. Against those numbers:
The $55 Pro Guide is the cheapest risk-reduction step in the entire project stack.
It is not more reading. It is pre-design due diligence — the step that tells you whether your lot can support any plan before you spend a dollar on design, permitting, or consultants.
The City pre-approves the building package. It does not pre-clear your setbacks, your trees, your drainage triggers, your utility capacity, or your construction access. Those are lot-specific — and they are exactly what the Pro Guide helps you evaluate first.
Frequently asked questions
What is a Seattle pre-approved DADU standard plan?
A detached ADU building plan that Seattle has pre-reviewed for a faster, more predictable permit path on eligible lots. Seattle's SDCI ADU page says many standard-plan projects can be permitted in about two to six weeks.
How fast can Seattle permit a pre-approved DADU?
Seattle says that in most cases homeowners can get a permit in two to six weeks when using a pre-approved standard plan on an eligible site — significantly faster than a custom DADU path, where review timelines vary by corrections, site complexity, and consultant coordination.
Who qualifies for the expedited standard-plan path?
Under the current Seattle Services Portal article (updated May 14, 2026): the project must use a pre-approved DADU standard plan, be on an eligible Neighborhood Residential lot, have no environmentally critical areas on the property, and keep total ground disturbance under 750 square feet.
Does pre-approved mean my lot is automatically approved?
No. You still need a site plan, parcel information, the standard-plan number, sewer paperwork, and compliance with current land use, stormwater, tree, and utility requirements. The City pre-approves the building package — not your lot.
Do I still need a WAC or side sewer permit?
Often yes. SPU says a WAC is required for most development projects in Seattle, typically issued in about 15 business days at no charge. As of October 1, 2025, SPU also handles all sanitary and wastewater side-sewer permitting, and cannot issue a side sewer permit for new construction until the related construction permit is issued.
How big can a Seattle DADU be?
Seattle's DADU tip sheet says a detached ADU in Neighborhood Residential zones cannot exceed 1,000 gross square feet, subject to certain code exclusions. Pre-approved standard plans currently in the ADUniverse gallery range from 288 sq ft (Haas Architectural studio) up to 1,000 sq ft (Fivedot Architects Schooner).
Can I build more than one ADU in Seattle?
Current Seattle ADU materials indicate up to two ADUs may be allowed on a lot with a principal dwelling unit, including the option of two detached ADUs, subject to applicable code standards. Verify current limits with SDCI at the time of your application.
Why buy a feasibility guide before buying a pre-approved plan?
Because the City pre-approves the building package — not your lot. Site-specific risks like trees, drainage, utilities, setbacks, and ECAs can stop or reshape the project even on the expedited path. The Pro Guide is the low-cost way to screen those risks before you spend on plans, permitting, or consultants.
This article is educational and preliminary. It is not legal advice, architectural advice, engineering advice, surveying advice, or an official determination by the City of Seattle. Zoning rules, permit requirements, and program eligibility can change. Verify all information against current SDCI and SPU guidance at the time of your application, and consult qualified professionals before making financial, design, permitting, or construction decisions.