"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
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Bellevue ADU & DADU rules, in plain English
Bellevue allowed only attached ADUs for three decades. Since July 1, 2025 it allows detached ADUs too. Here is what the code allows now, rule by rule. Written by MNBE founder Aharon Ben Elisha. Checked October 28, 2026.
LUC 20.20.120 DADUs allowed since Jul 1, 2025 2 ADUs per lot, any mix
The 2025 Update
What changed in Bellevue.
From 1993 until mid-2025, Bellevue's Land Use Code allowed only attached ADUs. A 2023 ordinance removed the owner-occupancy requirement, the ban on selling an ADU as a condominium and the registration rules, but still allowed attached units only. Ordinance 6851, adopted June 24, 2025 to carry out Washington's HB 1337 and HB 1110, allowed detached ADUs for the first time, effective July 1, 2025. The rules sit in LUC 20.20.120.
Bellevue's older ADU web page still describes the pre-2025 rules, and some outside sites still say DADUs are not allowed. We work from the code itself. The rules on your lot also depend on its zone, critical areas and trees, so treat this guide as the starting point. We confirm the current code for your address before design begins.
What we saw on our Bellevue attached ADU
We designed our Bellevue attached ADU when the code allowed only attached units: framed against the main house, with its own entry, full kitchen and bath. Watch it go up in the Bellevue ADU film, or see every stage on the project page.
Bellevue · LUC 20.20.120
Bellevue's ADU rules, by the numbers.
The four numbers homeowners ask about first. Check them against your lot with a feasibility study →
2
ADUs per lot
Attached, detached or one of each, including two detached ADUs.
1,200sq ft
Size cap
Per ADU, not counting up to 300 sq ft of parking or unheated storage.
24feet
DADU height
28 feet when built as an addition over an existing accessory building.
No
Owner occupancy
Removed in 2023, and state law now prohibits it.
The Code
Bellevue ADU rules, line by line.
Lots in districts that allow a single-family home or middle housing. Zone-specific numbers vary, so we confirm them for each lot.
| Rule | What Bellevue allows | Source |
|---|---|---|
| ADUs per lot | Up to two ADUs in any combination: two attached, one of each, or two detached. Detached ADUs count toward the lot's unit cap; attached ones don't. No new ADU on a unit lot already developed through a unit lot subdivision. | LUC 20.20.120 |
| Lot coverage | DADUs follow the middle housing standards: structure coverage generally 40% in LL-1 to SR-3 and 45% in SR-4 and denser districts, with separate impervious-surface limits. | LUC 20.20.538 |
| Size | 1,200 sq ft of floor area per ADU. Up to 300 sq ft of parking or unheated storage per ADU isn't counted. The city may allow more for an attached ADU that fills a whole floor, or when converting an existing detached accessory building. | LUC 20.20.120 |
| Floor area | With lot coverage, often the real limit on a DADU. Attached ADUs are exempt from the lot's floor area ratio (FAR); detached ADUs count, with a higher FAR allowed as units are added. | LUC 20.20.390 |
| Height | A detached ADU may be 24 feet tall, or 28 feet when built as an addition over an existing accessory structure. An attached ADU follows the house's height limit. | LUC 20.20.120 |
| Setbacks | Rear: 15 feet in the LL-1, LL-2, SR-1 and SR-2 districts, 10 feet in SR-3 and denser districts. Side: 5 feet. A DADU may sit on the lot line where the lot meets an alley. | LUC 20.20.538 |
| Minimum lot size | No ADU-specific minimum. | LUC 20.20.120 |
| Parking | None if the ADU is under 1,000 sq ft (not counting a garage) or within half a mile of a major transit stop. Otherwise one space per ADU. | LUC 20.20.120 |
| Owner occupancy | Not required. State law prohibits it. | RCW 36.70A.681 |
| Selling separately | An ADU can be sold as a condominium unit through the state condominium process. | RCW 36.70A.681 |
| Address | Bellevue assigns addresses for new units from an addressing site plan submitted with the permit. | Addressing site plan |
| Existing structures | A lawfully built garage or accessory building may become an ADU even if it doesn't meet today's setbacks or lot coverage. | LUC 20.20.120 |
| Design and registration | Bellevue removed its ADU-specific design and registration rules in 2023. ADUs still meet the zoning, building, tree and site standards. | LUC 20.20.120 |
| Home business | A lot can't have both an ADU and a home occupation permit. | LUC 20.20.120 |
| Trees | Significant trees are 6 inches in diameter and up; landmark trees, 24 inches and up. Protection zones and minimum tree credits apply, and a DADU counts as a unit for tree credits. | LUC 20.20.900 |
Checked October 28, 2026 against LUC 20.20.120, LUC 20.20.538, LUC 20.20.390, LUC 20.20.900, Ordinance 6851 and RCW 36.70A.681. Critical areas (LUC Part 20.25H) and the shoreline overlay add their own limits. A plain-English summary, not legal advice. The code governs, and we confirm it for your lot.
Your Lot
How we check a Bellevue lot for an ADU.
The code sets the outer limits. Your lot sets the real ones. This is the order we work in during the free site visit and feasibility.
01
Zone and overlays
We confirm your district and check for critical areas and the shoreline overlay, which can move or shrink the buildable area.
Zoning
02
Trees
We locate significant and landmark trees, their protection zones and the tree credits your lot needs.
Tree code
03
Fit the footprint
We test size, the 24-foot height, setbacks and floor area against your house, and whether attached or detached works better.
Footprint
04
Utilities
We check whether water, sewer and power can come from the house or need their own connections.
Utilities
05
Design and permit
We draw the plans in house, submit to Bellevue, answer corrections and carry the project through inspections.
City review
Reviews
What Seattle homeowners say about building with MNBE.
Verified five star reviews from owners we guided through ADU feasibility, permitting, and construction.
"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 · Bellevue ADU rules
Bellevue ADU questions we hear on site visits.
Short answers from the code. For your exact lot, call us or book the free site visit.
Yes. Since July 1, 2025, Bellevue allows detached ADUs under LUC 20.20.120. Before that, only attached ADUs were allowed.
Up to two, in any combination: two attached, one attached and one detached, or two detached. Floor area, setbacks, critical areas and trees decide what actually fits.
Up to 1,200 square feet of floor area per ADU, not counting up to 300 square feet of parking or unheated storage. For a DADU, the lot's floor area limit is often the tighter number.
24 feet, or 28 feet when built as an addition over an existing accessory structure. The code doesn't set a story limit, so the height is the deciding number.
Not if the ADU is under 1,000 square feet, not counting a garage, or within half a mile of a major transit stop. Otherwise the code asks for one space per ADU.
No. Bellevue removed its owner-occupancy rule in 2023, and state law (RCW 36.70A.681) now prohibits it.
Contact Us · Free Estimate
Tell us about your project.
We'll check your address against Bellevue's ADU code and get back to you within one business day with a clear next step.
Contact information
Thank you for considering MNBE. Thank you for considering MNBE. Tell us your address and we will tell you, in writing, what Bellevue's code allows on your lot. We respond within one business day, Monday through Saturday.
(206) 637 0044
info@mnbe-wa.com
2014 Fairview Ave Unit 2308, Seattle, WA 98121