DADU Builder in Sammamish, WA
Sammamish’s larger lots and established neighborhoods make it one of the best places on the Eastside to add a detached accessory dwelling unit. We turn that backyard space into a beautiful, permitted cottage — for family, for rental income, or the flexibility of both.
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DADU Rules in Sammamish
Sammamish adopted new development regulations effective January 1, 2025, and they’re friendlier than most homeowners expect:
- Two ADUs allowed per lot with a single-family home — attached, detached, or one of each
- Detached ADUs up to 1,000 sq ft and 24 feet tall
- Just 5-foot side and rear setbacks for a stand-alone backyard cottage
- No additional parking required when your parcel already has four or more spaces — garage and driveway count
- No owner-occupancy requirement — state law now prohibits one
- ADUs are exempt from the city's floor-area-ratio calculations
Verified July 2026 against Sammamish Municipal Code 21.05.010 (code effective January 2025). Septic lots need King County Public Health review, and significant trees need a removal permit — we plan around both from the first feasibility visit.
What Homeowners Use a Sammamish DADU For
Sammamish is known for its space, natural beauty, and established neighborhoods. That combination — plus steady Eastside rental demand — makes a backyard cottage one of the smartest ways to get more from a property you already love:
Aging parents
Comfort, privacy, and peace of mind — family close without sharing a hallway.
Guest house
Welcome family and friends in style — a real home, not an air mattress.
Home office or studio
A quiet, productive workspace in a private, natural setting.
Rental income
Consistent income in a strong Eastside market — long-term or flexible.
Our Design-Build Process
One accountable team from first sketch to final inspection — no juggling separate architects, permit expeditors, and contractors.
- 1. Consultation & feasibility — your lot, your goals, what Sammamish allows (including septic and trees)
- 2. Design — tailored to your property and how you'll use the space
- 3. Permitting — we handle the City of Sammamish submittals via MyBuildingPermit.com
- 4. Construction — one team, clear milestones, steady communication
- 5. Ready to use — inspections complete, ready for family or tenants
Sammamish DADU Questions, Answered
How many ADUs can I have on my Sammamish lot?
Two. Under the code that took effect January 1, 2025, a lot with a single-family home can add two accessory dwelling units — both attached, both detached, or one of each. A detached garage conversion can count as one of them.
What size and height DADU does Sammamish allow?
A detached ADU can be up to 1,000 square feet and up to 24 feet tall in every residential zone, with just 5-foot side and rear setbacks for a stand-alone cottage. ADUs are also exempt from the city’s floor-area-ratio calculations.
My Sammamish lot is on septic — can I still add a DADU?
Usually yes — and this is the most common Sammamish question we handle. Septic lots need King County Public Health review: added bedrooms count toward septic system sizing, and the DADU can’t sit on the drainfield or its reserve area. We check all of this in the first feasibility visit.
Will tree removal be a problem for my backyard cottage?
It’s manageable with planning. Removing a significant tree (conifers 8 inches in diameter or larger, deciduous 12 inches or larger) requires a City of Sammamish tree-removal permit and replacement planting — so we site your DADU to work with your trees, not against them.
Does Sammamish require parking or owner occupancy for an ADU?
There’s no owner-occupancy requirement — state law prohibits it. And if your parcel already has four or more parking spaces (garage and driveway count), no additional parking is required for the ADU.
Build Your Sammamish DADU
Schedule a free consultation and we’ll assess your property and lay out a clear path forward.