Shoreline Modern Cottage
Single-story 800 sqft DADU in Shoreline's Richmond Beach — light-gauge steel rainscreen, hyper-heat mini-split, designed for Sound Transit Lynnwood Link commuters.
- Type
- Detached ADU
- Sqft
- 800
- Beds / Baths
- 1 / 1
- Completed
- Jul 2024
- Duration
- 30 wks
- Budget
- $280,000
01 / BRIEF
What the owner asked for
Shoreline's 2022 DADU code update (SMC 20.40.235) made DADUs administratively permitted with no design review under 800 sqft. We designed exactly to that threshold to skip the discretionary review window.
02 / CHALLENGE
What stood in the way
Lot was within a King County Aquifer Recharge Area, restricting infiltration depth and requiring a sealed conveyance from any new impervious surface.
03 / APPROACH
How we solved it
Specified a fully sealed roof-to-grade drain leader system tied into the existing storm main. Used IBHS Fortified-equivalent roof detailing (clipped underlayment, fully adhered membrane at eaves) for long-term weather resilience.
04 / OUTCOME
What got delivered
Permit in 8 weeks (administrative track), build in 22 weeks. Owners' adult son moved in; the family avoided $2,400/month rent.
SPEC_05 / FACTS
Project specification
- Footprint
- 800 sqft single-story
- Bedrooms / baths
- 1 / 1
- Review track
- Administrative (no DR)
SCHEDULE_06 / PHASES
30-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 review8 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, 22-week build closeout.
MATERIAL_07
Materials
- CladdingLight-gauge steel rainscreen on 3/4" furring
- RoofTPO single-ply with clipped underlayment at eaves
SYSTEM_08
Systems
- Heating / coolingMitsubishi MUZ-FS12NAH hyper-heat, 12K BTU
- Water heatingAO Smith HPTU-50, hybrid heat pump
PERMIT_09 / RECORD
Permits & compliance
- Permit numberShoreline PB-24-100422
- StormwaterSealed conveyance to public main (ARA compliance)
METRIC_10 / OUTCOME
By the numbers
- 8 weeks
- Permit review
- $28,800
- Rent avoided/yr
LESSON_11 / FIELD NOTES
What we'd repeat
- Designing to 800 sqft exactly (vs. 825) opened the administrative permit track, saving 6+ weeks.
- Sealed conveyance in ARA zones is non-negotiable — infiltration trenches will not pass review.
ARCHIVE_∞ / MORE
Other field reports
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- 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 "Shoreline Modern Cottage"?
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 "Shoreline Modern Cottage" 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 "Shoreline Modern Cottage" 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 "Shoreline Modern Cottage" 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