"We hired MNBE to build our ADU in Bellevue, and the entire experience was amazing. They handled everything from foundations and framing to kitchen, siding, windows and HVAC."
Zena Heywood
Bellevue, WA · Attached ADU
4.8 STAR RATED40+ CUSTOMER REVIEWS
LICENSED · BONDED& FULLY INSURED
Detached ADU (DADU) construction for Seattle.
MNBE designs, permits, and builds detached ADUs end to end across Seattle, Bellevue, Kirkland, Redmond, Mercer Island, Sammamish, and the Eastside, one team, one fixed price contract. King, Snohomish & Pierce County.
Free DADU feasibility visit
HB 1337 fluent
Pre-approved plans
What A DADU Is
A detached, fully independent second home on your lot.
A DADU is a Detached Accessory Dwelling Unit: a small, fully independent home built on the same lot as your primary residence, with its own front door, its own kitchen, its own bathroom, and its own utility connections. No shared walls, no shared roof, a separate structure designed to function as a real second home. We are a detached ADU builder serving Seattle and the Eastside, from Magnolia and Green Lake to Bellevue, Kirkland, Redmond, Mercer Island, Sammamish, Issaquah, and Newcastle, and we handle the entire process from the first sketch to final inspection.
ADU is the umbrella category that also includes the attached ADU (AADU), the basement ADU, and the junior ADU. The detached DADU is the freestanding flavor, and across our Puget Sound ADU projects it is the version homeowners ask for first, because the privacy and rental value are the reason. Under Washington's HB 1337 rules you can add up to two units on most lots, with no owner occupancy requirement and no added off street parking. Start with the ADU and DADU overview, and after a free feasibility visit we tell you in writing whether a DADU is buildable on your lot.
Schedule Free Estimate
4.8 STAR RATED40+ CUSTOMER REVIEWS
LICENSED · BONDED& FULLY INSURED
Seattle DADU Rules · 2026
The numbers behind a detached unit.
Washington's HB 1337 reshaped what you can build detached on a Seattle lot.
1,000sq ft max
DADU footprint
Seattle base, up to 1,200 with a bonus floor on qualifying lots.
6 to 10months typical
Build window
Signed contract to certificate of occupancy on a typical lot.
5ft min setback
HB 1337 floor
The rear and side minimum most Seattle and Eastside cities apply.
20+
DADUs delivered
Detached units permitted and built across Puget Sound.
What does a DADU cost in Seattle?
Priced to your lot.
We do not publish a per square foot number because the average never matches your lot. Six factors move a DADU bid the most: lot access, whether a concrete truck can reach the site or we have to pump; soils and foundation, since a flat well drained lot takes a slab while a steep Magnolia or Mercer Island slope may need stem walls or piers; utility distance from your existing services; finish level, from a durable mid tier rental to a premium family unit; design complexity, where a pre-approved Seattle plan carries no surprises and a custom layout adds engineering; and critical area review on slopes, wetland buffers, or tree retention. After a free site visit you get a written fixed price that breaks out every line item, and the number we sign is the number we build to.
Every MNBE DADU includes
- Free written feasibility before any design contract
- Architectural drawings, including pre-approved DADU sets where they fit
- Permits, plan check corrections, and inspections
- Full construction by our own licensed crew, founder supervised
- One fixed price contract plus a one year workmanship warranty
How It Works
From feasibility to keys, one team.
No handoffs and no surprises. Here is exactly how your DADU goes from a buildable lot to a finished, rentable detached home.
01
Free written feasibility
We walk your lot, run the zoning code, check critical areas, and confirm HB 1337 in writing before any design contract.
Week 1
02
Fixed price contract
A written bid with every line item visible: permits, design, foundation, framing, mechanicals, finishes, and warranty.
Pre build
03
Permits
We prepare and submit to your city, use pre-approved DADU sets where they fit, and answer every correction ourselves.
We handle it
04
Build
One licensed crew, founder supervised, from foundation to finishes, with weekly homeowner updates.
Founder led
05
Keys & warranty
Final inspection, certificate of occupancy, and a finished DADU handed over with a one year workmanship warranty.
Move in ready
Reviews
What Seattle homeowners say about building with MNBE.
Verified five star reviews from owners who built their ADU, DADU, or renovation with us.
"We hired MNBE for a full renovation of our 100 year old home and the results exceeded expectations, structural upgrades, new insulation, a luxury bathroom, a high end kitchen, a new roof and mini split AC."
Dave Gierok
Sammamish, WA · Whole home renovation
"We hired MNBE for a major exterior renovation: a 900 sq ft custom deck with metal railings, full exterior painting and new siding. From start to finish the experience was exceptional, responsive, meticulous and patient."
Santosh S.
Redmond, WA · Deck & exterior
Schedule Free Estimate
4.8 STAR RATED40+ CUSTOMER REVIEWS
LICENSED · BONDED& FULLY INSURED
FAQs · What Clients Ask Us
DADU questions Seattle homeowners ask before they hire.
Practical answers from a builder who runs DADU permits and DADU job sites every week. Call us if yours isn't here. We answer the phone Monday through Saturday.
A DADU is a Detached Accessory Dwelling Unit, a fully separate small home on the same lot as the primary residence. ADU is the umbrella term covering attached units (AADUs), basement conversions, and junior interior conversions; the DADU is the freestanding version. In Seattle and the Eastside it's the most popular type for privacy, rental value, and clean separation.
On almost every single family lot, yes. Since HB 1337 took effect in 2023, every Seattle residential lot must allow at least two ADUs, and a detached unit is one valid option. Exceptions are pure rural residential zoning, lots where critical areas consume the buildable footprint, and a few historic overlay lots. We confirm yours with a free feasibility visit.
Seattle caps DADU size at 1,000 sq ft of gross floor area, with heights of 18 to 22 feet depending on lot configuration. Some lots qualify for a 1,200 sq ft envelope under bonus floor rules tied to tree retention or affordability. Bellevue, Kirkland, Redmond, and Mercer Island also allow 1,000 sq ft, and two story DADUs are permitted in most zones.
Plan on 6 to 10 months from signed contract to certificate of occupancy for a typical Seattle DADU: roughly 3 to 5 weeks of design, 2 to 4 months of plan-check at Seattle DCI, and 3 to 5 months of construction. Eastside cities like Redmond and Kirkland often run faster on permits, and Seattle's pre-approved DADU plans skip much of the architectural plan-check.
Cost varies lot to lot, so we don't publish a per square foot number that wouldn't apply to your project. The biggest budget drivers are lot access, soil and foundation conditions, utility distance, finish level, and design complexity. After a free site visit we deliver a written fixed price contract covering permits, design, build, and final landscaping, line by line.
We publish every question Seattle homeowners ask us about DADUs, permitting, and construction. Browse the full FAQ library for expert guidance.
View all FAQs
Contact Us · Free Estimate
Tell us about your DADU project.
We'll get back to you within one business day with a clear next step.
Contact information
Thank you for considering MNBE for your detached ADU project. We respond within one business day, Monday through Saturday.
(206) 637 0044
info@mnbe-wa.com
2014 Fairview Ave Unit 2308, Seattle, WA 98121