Greater Seattle Area

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What type of ADU are you considering?

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Size

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Seattle caps a detached unit at 1,000 sq ft. Select one to continue.

Layout

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Your lot

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Timing

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Permits alone take 8–16 weeks in Seattle, so “ASAP” still means a spring start.

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Your range is calculated. Add your details to see it right away. Not a sales call: we also check setbacks, utilities and slope on your property and send you a written range you can plan with.

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Your information is used only to respond to your request. Your instant estimate is a planning range from our 2026 Seattle ADU cost guide, not a quote. Every BB-Builders Pro project gets a line-item scope and a fixed price after a site visit.

Instant cost rangeNo obligationLine-item scope, fixed priceLicensed, bonded & insuredDesign-build: one team

Planning → Permits → Construction All handled by BB-Builders Pro.

Explore your options

Seattle's pre-approved DADU plans

These are the ten backyard-cottage designs currently pre-approved by the Seattle Department of Construction and Inspections. Homeowners have permitted them 199 times since 2020, and the City reports they clear permitting in about 80 days on average against 133 days for a custom DADU. We build any of them, or a custom design. Plan facts and designer details come from the City's ADUniverse gallery; photos are illustrative renderings, not the designers' drawings.

10plans pre-approved by SDCI

199permits issued on these plans since 2020 (38 in 2024)

80 vs 133 daysaverage permit time, pre-approved vs custom DADU

illustrative rendering of a one-level cedar cottage with a covered patio

1 bed · 2-bed optionIllustrative rendering

01 · CAST Architecture

Cedar Cottage

467 sq ft · 1 bed · 1 bath · plan licence $1,000

A one-level cottage with a flush entry, galley kitchen and a covered patio as the focus of the living space. Standard wood framing and a vented shed roof keep the cost down; a two-bedroom version is available for families.

Living on one level, accessible entry
Works on sloped and tree-filled sites
Targets Built Green 4-Star, all-electric

2D floor plan

Drawing from the designer's City of Seattle submission. Full plan set (PDF)

Plan details on the City's ADUniverse ›

illustrative rendering of a one-story traditional cottage

1 bed · accessibleIllustrative rendering

02 · Magellan Architects

MADADU

527 sq ft · 1 bed · 1 bath · plan licence $1,000

A 14'8" by 36' one-story unit that meets Seattle's accessible-DADU requirements, with a bedroom, full bath and kitchen. Common materials and a flexible roof type let it match almost any neighborhood.

Accessible single-story layout
Flexible roof and exterior materials
Rain-garden option, insulated walls

2D floor plan

Drawing from the designer's City of Seattle submission. Full plan set (PDF)

Plan details on the City's ADUniverse ›

illustrative rendering of a simple two-story rectangular cottage

2 bedIllustrative rendering

03 · Fivedot Architects

Schooner

1,000 sq ft · 2 bed · 1.5 bath · plan licence $1,000

A two-story family cottage: open living below, two bedrooms above, the larger one big enough for a home office. A simple rectangle on a heated slab, it can be mirrored or rotated and fits lots at least 30 feet wide.

Room for a family of four
Heated slab, ducted mini-split, solar-ready
Adapts to sloping sites

2D floor plan

Drawing from the designer's City of Seattle submission. Full plan set (PDF)

Plan details on the City's ADUniverse ›

illustrative rendering of a two-story cottage with a steep gable roof

2–3 bedIllustrative rendering

04 · Ahouse Studio

The Family

808–964 sq ft · 2–3 bed · 2 bath · plan licence $1,000

Bathrooms and kitchen sit in the middle of the plan so the rooms on either side can flex: the living room can become a third bedroom, the dining area a double-height space. Just under the size limit, buildable on lots from 30 feet wide.

Up to three bedrooms and two baths
Symmetrical plan, flexible entry location
Steep roof to limit view blockage

2D floor plan

Drawing from the designer's City of Seattle submission. Full plan set (PDF)

Plan details on the City's ADUniverse ›

illustrative rendering of a compact two-story wood-clad cottage

Studio – 2 bedIllustrative rendering

05 · HAAS Building

Urban Cottage

288 sq ft base · studio, 1 or 2 bed · plan licence from $900

A panelized "kit of parts" cottage that starts as a 288 sq ft studio and grows to one or two bedrooms, or a 940 sq ft two-story. Pre-cut structural insulated panels make the shell fast to assemble; several rooflines and finishes are included.

Start small, add bedrooms later
SIP panels: fast build, high insulation
Choice of roof and exterior styles

2D floor plan

Drawing from the designer's City of Seattle submission. Full plan set (PDF)

Plan details on the City's ADUniverse ›

illustrative rendering of a single-story gable cottage

1 bed · accessibleIllustrative rendering

06 · Artisans Group

Seattle DADU

600 sq ft · 1 bed · 1 bath · plan licence $1,000

A one-bedroom unit designed for aging in place: stairless entry, curbless shower and three-foot doorways are all options, with 9-foot walls, an open plan and a full cook's kitchen. Choose a gable or shed roof.

Accessible bath and entry options
Gable or shed roof to match the house
Insulated slab, energy-efficient envelope

2D floor plan

Drawing from the designer's City of Seattle submission. Full plan set (PDF)

Plan details on the City's ADUniverse ›

illustrative rendering of a tall gable cottage with living space upstairs

2 bedIllustrative rendering

07 · Yes Architecture

Sky House

600 sq ft · 2 bed · 1 bath · plan licence $1,000

Two bedrooms and a bath on the ground floor, the living space upstairs for privacy and longer views over the fences, plus a sleeping nook and deck in the gable. A 300 sq ft footprint keeps foundation work small; a corner entry lets the plan rotate to fit setbacks.

Upstairs living, high gabled ceilings
Cedar shake, lap or metal cladding
Options for 30- and 50-foot lots

2D floor plan

Drawing from the designer's City of Seattle submission. Full plan set (PDF)

Plan details on the City's ADUniverse ›

illustrative rendering of a compact two-level family cottage with an entry porch

2 bedIllustrative rendering

08 · Mobile Office Architects

MOA Family ADU

850 sq ft · 2 bed · 1 bath · plan licence $1,000

"Just the right amount": two separate bedrooms, a living room and a kitchen-dining space opening to a private patio, on a 16 by 26 foot footprint that fits tight sites. Built-in seating and storage do the work of extra square footage.

Two levels, family of four
Private patio off the living space
Choice of exterior finishes

2D floor plan

Drawing from the designer's City of Seattle submission. Full plan set (PDF)

Plan details on the City's ADUniverse ›

illustrative rendering of a minimal single-level pavilion with large windows

1 bed · flexibleIllustrative rendering

09 · Bohlin Cywinski Jackson

Edge House

432 sq ft · 1 bed · plan licence $1,000

A minimal, place-specific dwelling on a quick-ship bolted steel frame, with a utility "bar" holding the kitchen and bath. Owners choose the finishes, and movable interior components turn a live-work pavilion into sleeping space for up to four adults.

Bolted steel frame, fast to erect
Any exterior material to suit the site
Interior can change over time

2D floor plan

Drawing from the designer's City of Seattle submission. Full plan set (PDF)

Plan details on the City's ADUniverse ›

illustrative rendering of a one-bedroom unit above a garage with an exterior stair

1 bed · above garageIllustrative rendering

10 · Shape Architecture

Willow Creek DADU

650 sq ft · 1 bed · 1 bath · plan licence $750

Living space above a ground-floor garage or workshop: open kitchen, living and dining, a full bath, bedroom, laundry and pantry upstairs, with an exterior stair and landing that double as outdoor space and covered storage below.

Keeps the garage or workshop below
Exterior stair and private deck entry
Rent the unit, keep the garage

2D floor plan

Drawing from the designer's City of Seattle submission. Full plan set (PDF)

Plan details on the City's ADUniverse ›

ADUniverse 2.0 is coming. The City selected 15 new ADU and middle-housing designs from 110 submissions and expects the new pre-approved plans to be available from January 2027. If your timeline is next year, we'll walk you through both catalogs.

Usage and timing figures are from the City of Seattle 2023 and 2024 ADU Annual Reports. Pre-approved plans are licensed directly from their designers ($750–$1,325 per the City's gallery); BB-Builders Pro is not affiliated with them. Pre-approved does not mean automatic approval: every lot still needs a site plan and a review of setbacks, utilities, drainage and slope, which is the part we handle.

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A better use of space

Turn unused space into something more

Space for family

A parent close enough to help, with their own kitchen, bath and front door.

Rental income

A finished Seattle backyard cottage rents for about $2,000–$3,500 a month.

Flexible living

A home office, a guest suite, or a place for adult kids to land.

Designed for your lot

Setbacks, trees, slope and the sewer line decide the design. We check them first.

The BB-Builders Pro approach

Planning, permits & construction

One team from the first site visit to the final walkthrough, with everything in writing.

Planning

We walk the lot, confirm what it allows, and turn the idea into drawings and a line-item scope you can react to before anything goes to the city.

Permits

Seattle's permit office takes about 8–16 weeks to review an ADU. We prepare the set, answer the city's comments and keep you posted on where it sits.

Construction

Same crew, same project manager, weekly updates in writing, and every change order signed before the work happens. The number you sign is the number you pay.

Why BB-Builders Pro

Build your ADU with confidence

Line-item scope, fixed price

You see exactly what's included before we start. A bid that's 30% cheaper is usually missing 30% of the scope.

Design-build, one team

Planning, permits and construction under one roof, so nothing falls between an architect and a builder.

Everything in writing

Detailed scope, schedule, signed change orders and weekly progress updates. You always know what comes next.

Licensed, bonded & insured

Washington State licensed and bonded, with full general liability coverage, and hundreds of local reviews to check.

Your next chapter starts here

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