"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
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Sammamish ADU & DADU rules, in plain English
What Sammamish's code allows for attached and detached ADUs since January 2025, rule by rule. Written by MNBE founder Aharon Ben Elisha. Checked October 28, 2026.
SMC 21.05.010 In force since Jan 1, 2025 2 ADUs per lot, any mix
The Update
What changed in Sammamish.
Sammamish rewrote its ADU rules with the 2024 Comprehensive Plan update. Ordinance O2024-578 took effect on January 1, 2025. It allows two ADUs of any type, removed the owner-occupancy rule, and exempts ADUs from the house's floor area and hardscape limits. The rules sit in SMC 21.05.010.
The city's older ADU handout from 2023 is still online and shows one DADU, an 18-foot height and two parking spaces. The code replaced all of that, so we work from the code itself. Critical areas, common on wooded and sloped Sammamish lots, add their own limits.
Rules for other cities are in our ADU rules by city guide.
Sammamish · SMC 21.05.010
Sammamish'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
Two attached, two detached or one of each.
1,000sq ft
Size cap
Larger for an ADU wholly inside the existing house.
24feet
DADU height
In every zone, so two stories are possible.
0
FAR and hardscape
ADUs don't count toward the house's floor area or hardscape limits.
The Code
Sammamish ADU rules, line by line.
The main single-family zones. Zone-specific numbers vary, so we confirm them for each lot.
| Rule | What Sammamish allows | Source |
|---|---|---|
| ADUs per lot | Two ADUs on a lot with one detached house, in the R-1 to R-18 zones: two attached, two detached (in one or two buildings), one of each, or a conversion. | SMC 21.05.010 |
| Size | 1,000 sq ft. An ADU wholly inside the existing house can be up to 50% of the house or 1,000 sq ft, whichever is larger. | SMC 21.05.010 |
| Floor area and hardscape | ADUs are exempt from the house's floor area ratio and hardscape limits. | SMC 21.04.030 |
| Height | 24 feet for a DADU in every zone. | SMC 21.04.030 |
| Setbacks | A stand-alone DADU: 5 feet side and rear. A DADU combined with a garage or similar building follows accessory-building setbacks: 10 feet side and rear in R-1 to R-8, 5 feet in R-12 and R-18. Front setbacks follow the zone. | SMC 21.04.030 |
| Minimum lot size | No ADU-specific minimum. | SMC 21.05.010 |
| Parking | No added space when the lot already has four or more, and none within a quarter mile of an existing or planned transit stop. | SMC 21.06.030 |
| Owner occupancy | Not required. The rule was repealed in 2025, and state law prohibits it. | RCW 36.70A.681 |
| Existing structures | Converting an existing building, such as a detached garage, is allowed. | SMC 21.05.010 |
| Design and covenant | No design-matching rule and no recorded covenant in the current code. | SMC 21.05.010 |
| Trees | Significant trees are conifers 8 inches in diameter and up and deciduous trees 12 inches and up. Retention and removal limits depend on the zone and the project. | SMC 21.03.060 |
Checked October 28, 2026. Sources: SMC 21.05.010, SMC 21.04.030, SMC 21.06.030, SMC 21.03.060, the city’s 2024 Comprehensive Plan page and RCW 36.70A.681. Critical areas and their buffers 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 Sammamish 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 zone and check Sammamish's maps for critical areas, shoreline and slopes, which can move or shrink the buildable area.
Zoning
02
Trees
We locate the trees the code protects and their root zones before we place the ADU.
Tree code
03
Fit the footprint
We test size, height, setbacks, coverage and floor area against your house, and whether an existing building can be converted.
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 Sammamish, 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
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FAQs · Sammamish ADU rules
Sammamish 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 a lot with one detached house: two attached, two detached, or one of each. Critical areas and their buffers often decide where a DADU can go.
1,000 square feet. An ADU built wholly inside the existing house can be up to half of the house or 1,000 square feet, whichever is larger.
24 feet in every zone, which fits a two-story DADU.
No. Sammamish exempts ADUs from the house's floor area ratio and hardscape limits.
Not if the lot already has four or more spaces, or sits within a quarter mile of a transit stop.
Contact Us · Free Estimate
Tell us about your project.
We'll check your address against Sammamish'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 Sammamish'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