"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
FIVE-STAR RATEDRATED ON GOOGLE
LICENSED · BONDED& FULLY INSURED
What Drives the Cost of an ADU in Seattle
There is no honest per square foot price for an ADU or DADU. Your lot, the design and the city set most of the number. Here is what moves the price, and how MNBE turns it into one written fixed price after a free site visit. Seattle & the Eastside.
Priced to your lot
One fixed price
Founder supervised
What Moves The Price
Eight things that set the cost of an ADU.
Floor area is only one of them. These are the factors we look at on every lot before we price a DADU, an attached ADU or a basement conversion.
01
Your lot
Slope, soil and the room crews and equipment have to work set the foundation and site work. A flat, open backyard and a steep or tight one are very different jobs.
Set by your lot
02
Sewer, septic and utilities
Most ADUs connect to water, sewer and power through the main house's existing lines. When the ADU needs its own connections to the city utilities, the price goes up. If the house is on septic, the ADU usually needs a larger septic system, or a second one where the lot has room, and that is one of the biggest costs an ADU can carry.
Set by your lot
03
Detached, attached or conversion
A detached DADU is a full new building. An attached ADU shares a wall with the house and connects to it. A basement conversion works inside an existing structure.
Set by the ADU type
04
Size, stories and layout
Bedrooms, bathrooms and a second story change structure, plumbing and stairs. A simple footprint builds more efficiently than a complicated one.
Set by the design
05
Foundation and structure
Soil conditions and the design decide the foundation and the engineering. Large windows and wide openings leave less wall to brace the building, so the structure needs stronger and more costly support. A second story adds structural work too.
Set by the engineering
06
City requirements
Each city has its own review. Trees on or near the site can require an arborist and tree protection, and some lots need stormwater or drainage work.
Set by the city
07
Existing structures
Taking down an old garage or shed, or rebuilding an old structure on its footprint, adds work before the new build starts.
Set by what is there
08
Finish level
Cabinets, counters, flooring, windows, fixtures and the exterior cladding are the part you choose. The same plan can be built at very different finish levels.
Set by you
How MNBE prices your ADU.
Priced to your lot.
We do not quote from a price list. We walk your property, confirm what the lot supports, and look at every factor above with you. Then you get a written fixed price that covers design, permits and construction, and the number we sign is the number we build to.
“The three things I see raise the cost of an ADU most often: a house on septic, which usually means a larger septic system or a second one; an ADU that needs its own connection to the city utilities instead of tying into the main house; and large windows and openings, which leave less wall to hold up the structure. We check all three at the first site visit.”
Aharon Ben Elisha, Founder & Builder
Every MNBE fixed price includes
- Architectural drawings and design
- Structural engineering coordination
- Permits, plan check corrections, and inspections
- Full construction by our own licensed crew
- One fixed price contract, founder supervised
How It Works
From feasibility visit to keys, one team.
No handoffs and no surprises. Here is exactly how your ADU goes from idea to a finished, rentable home, typically 6 to 10 months end to end.
01
Free feasibility visit
We walk your lot, confirm it supports an ADU, and talk through your goals before you commit to design.
No cost
02
Design & feasibility
Architectural drawings, structural coordination, and a written bid, so you know the number before permits.
3-5 weeks
03
Permits
We submit to Seattle DCI or your Eastside city, answer every plan check correction ourselves, and schedule inspections.
2-4 months
04
Build
One licensed crew, founder supervised, from foundation to finishes, on the fixed price we signed.
3-5 months
05
Keys
Final inspection, certificate of occupancy, and a finished ADU ready to live in or rent.
Move in ready
Reviews
What Seattle homeowners say about building with MNBE.
Verified five star reviews from owners who built their ADU, DADU or new home 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
Redmond, WA · DADU
"My mom hired MNBE Construction for her two-bedroom DADU in Seattle, and watching the process up close was impressive. They did it all: design, architectural plans, the building permit, and the full construction. … The communication was excellent and there were never any surprises."
Maryam Z.
White Center, WA · ADU
Schedule Free Estimate
FIVE-STAR RATEDRATED ON GOOGLE
LICENSED · BONDED& FULLY INSURED
FAQs · What Clients Ask Us
ADU cost questions homeowners ask us.
Straight answers about pricing from a builder who prices ADUs on real lots every month. Call us if yours isn't here.
Because floor area is not what sets most of the price. The lot, the utility connections, the foundation, the city requirements and the finish level move the total far more than square footage does. Two ADUs of the same size can be very different jobs, so we walk your property first and price your project, not an average.
After a free feasibility visit at your property. We confirm what your lot supports, talk through your goals and the design, and then give you a written fixed price that covers design, permits and construction. The number we sign is the number we build to.
Architectural drawings and design, structural engineering coordination, permit submittal, plan check corrections and inspections, and full construction from foundation to finishes, founder supervised.
Usually, because a detached DADU is a complete new building with its own foundation, roof and utility runs. An attached ADU shares a wall and some systems with the house. The lot and the design still decide which option makes more sense for you, and we compare both at the site visit when your lot allows both.
Start with MNBE's free site visit before you finalize plans. Choose a simple layout and a spot on the lot that limits excavation, tree impacts and long utility runs. Check whether the house's existing water, sewer and power can serve the ADU, and if the house is on septic, find out early whether it needs a larger system. Compare attached, detached and conversion options, balance large windows and doors with the structure, and choose finishes early.
Contact Us · Free Estimate
Tell us about your 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 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