Sammamish Modern Farmhouse ADU
1,000 sqft modern farmhouse DADU on a 1-acre Sammamish Plateau lot — board-and-batten Hardie, blackened steel roof.
- Type
- Detached ADU
- Sqft
- 1,000
- Beds / Baths
- 2 / 2
- Completed
- Jan 2025
- Duration
- 34 wks
- Budget
- $360,000
01 / BRIEF
What the owner asked for
Empty-nesters wanted a DADU for the primary home to be downsized into eventually, with the current main home becoming the rental. Required Sammamish SMC 21A.30.305 compliance and on-site septic verification.
02 / CHALLENGE
What stood in the way
On-site septic system was 2003-vintage and sized for the existing 3-bed/2-bath home only. Adding 2 bedrooms triggered a Health Dept review.
03 / APPROACH
How we solved it
Worked with King County Public Health to upsize the septic (added 250-gallon polylock chamber + 80 LF of new drainfield).
04 / OUTCOME
What got delivered
Permit in 14 weeks (incl. septic review), build in 20 weeks. Long-term plan is to rent the main house in 2026.
SPEC_05 / FACTS
Project specification
- Footprint
- 1,000 sqft single-story
- Bedrooms / baths
- 2 / 2
- Septic
- Existing + 250 gal + 80 LF drainfield
SCHEDULE_06 / PHASES
34-week delivery
- 01Feasibility & design4–6 wks
Site survey, zoning memo, schematic plans, owner review.
- 02Construction docs3–4 wks
Structural, MEP, energy compliance, permit-ready set.
- 03Permit review14 wks
City corrections, utility sign-offs, building permit issued.
- 04Site work + foundation3–4 wks
Erosion control, excavation, footings, slab or stem wall.
- 05Framing + dry-in5–6 wks
Floor, walls, roof, windows, weather-resistive barrier.
- 06MEP rough-in + insulation4–5 wks
Plumbing, electrical, HVAC, blower-door prep.
- 07Finish + cabinetry6–8 wks
Drywall, paint, flooring, cabinets, tile, fixtures.
- 08Inspections + handover1–2 wks
Final inspections, punch-list, 20-week build closeout.
MATERIAL_07
Materials
- CladdingHardie board-and-batten, BM Simply White
- RoofStanding seam 24-ga, matte black
SYSTEM_08
Systems
- Heating / coolingDucted Daikin Fit 24K BTU
PERMIT_09 / RECORD
Permits & compliance
- Permit numberSammamish PR2024-0612
- Septic reviewKC Health SE24-1188 (approved)
METRIC_10 / OUTCOME
By the numbers
- +2 bedrooms equivalent
- Septic capacity added
LESSON_11 / FIELD NOTES
What we'd repeat
- On septic lots, always pull the original septic record (KC Health) before sizing the ADU — septic upsizes can add 3–8 weeks and $12–35K.
ARCHIVE_∞ / MORE
Other field reports
- REF_4492 · Detached ADUBallard Monolith
A 1,000 sqft two-story DADU clad in vertical western red cedar with floor-to-ceiling industrial glazing — long-term rental on a 4,800 sqft Ballard lot.
- REF_4376 · Attached ADUBellevue Wing
A 720 sqft side-yard AADU grafted onto a 1962 craftsman in West Bellevue — independent entry, separate utilities, no shared interior wall openings.
- REF_4218 · Garage ConversionKirkland Garage Studio
A two-car detached garage converted into a high-end work-from-home studio with a 6'x6' fixed skylight — Kirkland's Norkirk neighborhood.
Frequently asked
Can I tour a project like "Sammamish Modern Farmhouse ADU"?
Yes — we typically have 6–10 ADUs in framing or finish at any time across the Puget Sound, so we can usually arrange a site walk on a project at the same stage you're planning. For completed projects, tours depend on the current owner's availability and privacy preferences. Request a tour and we'll match you to the closest active or completed project that resembles "Sammamish Modern Farmhouse ADU" in size, configuration, and AHJ.
What did this project actually cost?
Each project page includes the all-in cost range for the size and configuration shown, scaled to 2026 prices. Actual contract value at time of build is confidential to the client, but the range we publish is anchored in real numbers from our bid archive — not aspirational pricing. For a tailored estimate against your lot, run our feasibility study or use the cost calculator.
Go deeper: Read the Five hidden ADU costs that wreck Puget Sound budgets guide
How long did this project take?
Most projects of this size and configuration run 9–14 months from contract to certificate of occupancy: 6–8 weeks of design, 8–16 weeks of permit, 18–26 weeks of construction. Schedule variance is driven by AHJ workload, owner selection pace, and field-discovered conditions during demo or excavation. We publish a Gantt at contract and update it weekly.
Go deeper: Read the Eastside deck cost & permits: cedar, IPE, composite (2026) guide
Could you build "Sammamish Modern Farmhouse ADU" again on my lot?
Often yes — most of our projects are anchored on repeatable design DNA (envelope details, structural assemblies, MEP standard layouts) that adapt to different lot conditions with modest configuration changes. We'll review your lot's zoning, soils, and access to confirm fit. Where the original layout doesn't fit, we propose the closest workable adaptation that preserves the look you liked.
What inspections did "Sammamish Modern Farmhouse ADU" go through?
Standard Puget Sound ADU inspection sequence applied: footing, underfloor MEP, framing, plumbing rough, electrical rough, mechanical rough, insulation, drywall nailing, shower pan, gas piping, final building, final plumbing, final electrical, final mechanical, and final energy verification (blower-door ≤3 ACH50). All passed with no notable callbacks — typical for our builds because we run internal QA checklists at each milestone.
INTERNAL_LINKS / Deep Map