Detached ADU
DADU builder for Seattle and the Eastside.
Detached ADUs designed, permitted, and built end to end. Built by Aaron Elisha across Seattle, Bellevue, Kirkland, Redmond, Mercer Island, Sammamish, Issaquah, and Newcastle.
Written by Aaron Elisha, founder of MNBE Construction & Development. WA license MNBECCD770R9. Updated 2026.
What a DADU actually is.
A DADU is a Detached Accessory Dwelling Unit. A small, fully independent home built on the same lot as a 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.
ADU is the umbrella category. It also includes Attached ADUs, basement ADUs, and Junior ADUs. The DADU is the freestanding flavor and, across roughly 20 Puget Sound ADU projects, it is the version homeowners ask for first. The privacy is the reason.
How a DADU compares.
| Type | Detached? | Max sq ft (Seattle) | Build window | Best for |
|---|---|---|---|---|
| DADU | Yes, freestanding | 1,000 (1,200 bonus) | 6 to 10 months | Privacy + rental income |
| AADU | No, shares a wall | 1,000 | 5 to 8 months | Tighter lots, lower cost |
| Basement ADU | No, basement conversion | ~800 | 4 to 7 months | Existing finished basement |
| Junior ADU | No, interior conversion | Under 500 | 2 to 4 months | Smallest unit, fastest path |
Note · Build windows are MNBE crew pace on a typical Seattle lot. Critical-area constraints, custom design, and city-specific permit speeds shift the numbers.
Chapter 02 · Why Detached
Four reasons a DADU outperforms every other ADU type.
These are the practical advantages that show up across nearly every Seattle and Eastside DADU project we deliver.
Rental income that pays the mortgage
A 1,000 sq ft DADU in Magnolia, Green Lake, Bellevue, or Kirkland rents quickly because inventory is tight and the demographic is right. Long-term rents in central Seattle and central Eastside neighborhoods regularly carry the principal and interest on the primary mortgage.
Privacy that attached units cannot match
An aging parent or adult child has their own front door, their own kitchen, their own quiet. A renter has their own address, their own mail slot, and no overlapping HVAC noise. Detached buys the kind of flexibility that attached and basement units simply cannot.
Lot value that survives a market cycle
Two legal dwellings on a single lot is a fundamentally different asset than one. Appraisers price it differently. Lenders treat it differently. When the market turns and single-family sales slow, lots with a finished DADU keep moving.
Pre-approved plans pull months out of the calendar
Seattle's pre-approved DADU program is the fastest legal path to a finished detached unit inside the city. We have built from multiple pre-approved sets and know which plans fit which lots and which finish packages match which budgets.
Six factors that move every DADU bid.
We don't publish per-square-foot pricing because the average never matches your lot. Bigger bars mean a larger swing on the final number.
Get a written fixed price →01Lot access
high impactCan a concrete truck reach the site, or do we pump? Tight Seattle infill and steep Eastside hillside lots can add five-figure access cost alone.
02Soils + foundation
high impactFlat well-drained lot takes a slab. Steep Magnolia or Mercer Island slope may require stem walls, piers, or a grade beam. Engineered to what soils say.
03Utility distance
mediumRunning electrical, water, sewer 25 feet from existing services is one cost. 80 feet across finished landscape is another. Panel upgrade adds a line.
04Finish level
high impactSame 1,000 sq ft DADU can be a durable mid-tier rental or a premium family unit. Cabinets, appliances, tile, plumbing, lighting move the budget more than people expect.
05Design complexity
medium-highPre-approved Seattle plan or stock layout: no surprises. Custom design with cantilevers or stepped foundations: more engineering, more sequencing.
06Critical-area review
medium-highSteep slopes, wetland buffers, tree retention, stream corridors. Zoning untouched under HB 1337 but the review still applies. CAR study + mitigation is real time and budget.
DADU rules across the Eastside and Seattle.
The state floor under HB 1337 is the same everywhere. Local execution is not. Eight cities MNBE works in most often, side by side.
- Seattle
Pre-approved DADU program available. Up to 1,000 sq ft, 1,200 with bonus floor. SDCI 3 to 6 month permit window.
- Bellevue
Code updated 2024. Two ADUs allowed per lot. Critical-area review common in older neighborhoods.
- Kirkland
Fastest Eastside permit timelines. ADU and DADU permits typically issue in 8 to 14 weeks.
- Redmond
HB 1337 fully implemented. Strong DADU demand from tech families. Permit office moves 30 to 50 percent faster than Seattle.
- Mercer Island
Two ADUs now allowed (was one). Critical-area review tightly enforced. Expect a CAR study on most lots.
- Sammamish
Lower DADU volume than central Eastside. Larger lots common, which means larger buildable envelopes.
- Issaquah
Older HOA covenants common. Covenant review part of feasibility. Two ADUs allowed in most residential zones.
- Newcastle
Hillside lots common. Engineering scope drives more of the budget than zoning. Two ADUs allowed under HB 1337.
Note · Status as of 2026. Codes change. Verify with a feasibility study before commissioning design.
What we commit to on every DADU build.
Four commitments that show up before, during, and after the build. Same on every DADU we deliver.
- Week 1
Free written feasibility
Before any design contract, we walk your lot, run the zoning code, check critical areas, confirm HB 1337 application, and tell you in writing whether a DADU is buildable. We do not sell design work on lots that cannot finish a permit.
- Pre-build
Fixed-price contract, line by line
After feasibility, you get a written fixed-price bid with every line item visible: permits, design, foundation, framing, mechanicals, finishes, landscaping, warranty. Compare apples to apples against any other contractor.
- End to end
Aaron on the job site
The license holder is on the build. Weekly homeowner updates. Same phone number from consultation through final inspection. Saturday calls answered by the person who knows your project, not a dispatcher.
- After handover
1-year warranty + 25-year docs
One year full workmanship warranty on the entire DADU. Major systems carry their manufacturer warranties on top. We hand over a full warranty packet at completion with every paper you need for the next 25 years.
Recent MNBE Work
Four projects MNBE has delivered across Seattle and the Eastside.
Every project below was permitted, supervised, and delivered by the MNBE team. Walkthrough videos and full project pages coming soon.
DADURedmond DADU
Detached · 100-year structure rebuilt to studs · 2025
AADUBellevue Attached ADU
Attached · Navy lap siding · Verified Google review · 2024
DADUIn ProgressMagnolia DADU
Detached · Seattle · In finish phase · 2026
New BuildLake Washington Custom Build
Addition + full rebuild · Premium leaded-glass entry
"On the Redmond DADU we took a 100-year-old structure that had been sitting unused on the lot and rebuilt it to the studs. New foundation, new framing, new roof, new windows, new mechanicals, new everything. Same MNBE process on a new ground-up DADU as on a structure conversion. Same craftsmanship either way."
Aaron Elisha · Founder, MNBE Construction & Development
Keep Reading
The decisions a DADU build touches.
The Law
HB 1337 Explained
The 2023 Washington law that unlocked DADUs across Seattle and the Eastside.
Read the guide →The Sibling
Attached ADU (AADU)
When attached beats detached on cost, lot fit, or schedule.
Compare AADU vs DADU →Faster Path
Seattle Pre-Approved DADU Plans
The program that compresses DADU permits by months.
See the program →Frequently Asked
DADU questions Seattle homeowners ask before they hire.
Twelve practical answers from a builder who runs DADU permits and DADU job sites every week. If yours is not here, call us. Two minutes on the phone usually clears it up.
Still have questions?
We answer the phone Monday through Saturday. Two minutes on the call usually gets you further than an hour online.
A DADU is a Detached Accessory Dwelling Unit, a fully separate small home built on the same lot as a primary residence. ADU is the umbrella term for any accessory dwelling, which also includes attached units (AADUs) sharing a wall with the main house, basement conversions, and junior interior conversions. The DADU is the freestanding version. In Seattle and the Eastside, it is by a wide margin the most popular ADU type because it preserves privacy, builds the most rental value, and triggers the cleanest separation between the primary home and the second unit.
On almost every single-family lot, yes. Since HB 1337 took effect in 2023, every Seattle residential lot must allow at least two ADUs in some combination, and a detached unit is one valid option. The exceptions are lots in pure rural-residential zoning, lots with critical-area constraints that consume the buildable footprint, and a small number of historic-overlay lots. We confirm your specific lot during a free feasibility visit before any design work starts.
Seattle's current code caps DADU size at 1,000 sq ft of gross floor area, with a maximum height of 18 to 22 feet depending on lot configuration. Some lots qualify for a larger 1,200 sq ft envelope under the bonus-floor rules tied to tree retention or affordability. On the Eastside, Bellevue, Kirkland, Redmond, and Mercer Island all allow up to 1,000 sq ft as well. Two-story DADUs are permitted in most zones, which is how a 1,000 sq ft footprint becomes a comfortable two-bedroom unit with a real kitchen and a full bath.
Plan on 6 to 10 months from signed contract to certificate of occupancy for a typical Seattle DADU. The breakdown is 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 generally run faster on permits, which can compress the total further. Pre-approved DADU plans inside Seattle can compress more by skipping much of the architectural plan-check phase. Aaron's crews build faster than the regional average, and we hold the schedule we put in writing.
Cost depends on factors that vary lot to lot and finish to finish, so we don't publish a per-square-foot number that would not apply to your project. The variables that move the budget most are lot access (whether trucks can reach the build site without crane work), soil conditions (a steep or rocky lot drives up foundation costs), utility distance, finish level (cabinets, appliances, flooring, lighting, and plumbing fixtures), and design complexity. After a free site visit, we deliver a written fixed-price contract that breaks out every line item, including permits, design, build, and final landscaping.
Yes, both are allowed in Seattle and most Eastside cities, but specific rules vary. Seattle requires short-term rental operators to register and limits non-primary-residence STRs. Long-term rentals of 30 days or more are generally unrestricted across the region. Bellevue and Kirkland have their own short-term rental regulations. We walk through the specific rules for your city during the consultation so the income model you want lines up with what your jurisdiction actually permits.
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