"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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King County ADU & DADU rules, in plain English
The rules for unincorporated King County, including White Center, North Highline and Skyway, since the 2024 Comprehensive Plan update. Written by MNBE founder Aharon Ben Elisha. Checked October 28, 2026.
KCC 21A.08.030 Ordinance 19881 Urban: 2 ADUs · Rural: 1
The Update
What changed in King County.
Unincorporated King County, including White Center, North Highline and Skyway, updated its ADU rules with the 2024 Comprehensive Plan. Ordinance 19881, adopted December 10, 2024, allows two ADUs on urban lots and removed the parking requirement. The rules sit in KCC 21A.08.030.
The county's online ADU FAQ still shows the old rules: one ADU, owner occupancy and a 5,000 sq ft minimum lot. The code and the county's March 2026 ADU handout replaced them, so we work from those.
What we saw on our White Center ADU
We built a 500 sq ft two-bedroom ADU in White Center from a bare grass lot, through King County permits and inspections. Watch it in the White Center ADU film, or see every stage on the project page.
Rules for other cities are in our ADU rules by city guide.
King County · KCC 21A.08.030
King County's ADU rules, by the numbers.
The four numbers homeowners ask about first. Check them against your lot with a feasibility study →
2
ADUs on urban lots
Attached, detached or one of each. Rural lots: one.
1,000sq ft
Heated area
Up to 1,500 on urban lots by trading unheated space.
35feet
DADU height
The base height in the urban R-1 to R-8 zones.
0
Parking spaces
No ADU parking, urban or rural.
The Code
King County ADU rules, line by line.
The main single-family zones. Zone-specific numbers vary, so we confirm them for each lot.
| Rule | What King County allows | Source |
|---|---|---|
| ADUs per lot | Urban areas: two ADUs, one attached and one detached, two attached, or two detached in one or two buildings. Rural areas: generally one ADU, with lot-size conditions for a detached unit; a rural-town lot of at least 3,200 sq ft can qualify. Forest (F) zones don't allow ADUs. | KCC 21A.08.030 |
| Size | 1,000 sq ft heated plus 1,000 sq ft unheated. On urban lots, unbuilt unheated area can be added as heated space, up to 1,500 sq ft heated. An ADU wholly inside the house's basement or attic is exempt from the cap, and a detached ADU's basement isn't counted. | KCC 21A.08.030 |
| Height | The zone's base height: 35 feet in the urban R-1 to R-8 zones, 40 feet in rural RA zones. Two-story DADUs are allowed. | KCC 21A.08.030 |
| Setbacks | Urban R-4 to R-8 zones: 10 feet from a street, 5 feet from interior lot lines. | KCC 21A.09 |
| Impervious surface | Urban limits: 55% in R-4, 70% in R-6, 75% in R-8. Smaller R-4 and R-6 lots use the next zone's figure. | KCC 21A.09 |
| Minimum lot size | No urban minimum in the ADU code. A health approval or sewer certificate may be needed. | KCC 21A.08.030 |
| Parking | None required, in urban or rural areas. | KCC 21A.08.030 |
| Owner occupancy | Not required. State law prohibits it in urban growth areas. | RCW 36.70A.681 |
| Notice on title | A notarized notice on title is recorded before the permit and runs with the land. | County affidavit |
| Existing structures | On urban lots, an existing structure such as a garage can be converted even where it doesn't meet today's setbacks or impervious limits. | KCC 21A.08.030 |
| Street improvements | Not required for an ADU on an urban lot. | KCC 21A.08.030 |
| Critical areas | Wetlands, streams, steep slopes, landslide and erosion hazards and aquifer recharge areas follow KCC 21A.24. | KCC 21A.24 |
Checked October 28, 2026. Sources: KCC Title 21A, the county's March 2026 ADU handout, its notice on title affidavit and RCW 36.70A.681. A plain-English summary, not legal advice. The code governs, and we confirm it for your lot.
Your Lot
How we check a King County 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
Urban or rural
We confirm whether your lot is in the urban growth area, which sets one ADU or two, and its zone.
Zoning
02
Critical areas
We check the county's maps for wetlands, streams, steep slopes and landslide areas.
KCC 21A.24
03
Fit the footprint
We test size, height, setbacks and impervious surface against your house, and whether a garage can be converted.
Footprint
04
Sewer or septic
We confirm the sewer district or the septic approval the ADU needs.
Utilities
05
Design and permit
We draw the plans in house, record the notice on title, submit to King County and carry the project through inspections.
County 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
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FAQs · King County ADU rules
King County ADU questions we hear on site visits.
Short answers from the code. For your exact lot, call us or book the free site visit.
Two on an urban lot in unincorporated King County: one attached and one detached, two attached, or two detached.
1,000 square feet of heated space plus 1,000 square feet of unheated space. On urban lots you can trade unbuilt unheated area for heated space, up to 1,500 square feet heated.
No. The current code requires no ADU parking, in urban or rural areas.
No. It still shows the pre-2025 rules. The code, KCC 21A.08.030, and the county's March 2026 handout are current.
Rural lots generally get one ADU, with lot-size conditions for a detached unit, and Forest zones allow none. Septic and well approvals often decide the design.
Contact Us · Free Estimate
Tell us about your project.
We'll check your address against King County'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 King County'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