SPEC_C / BURIEN · DADU · Verified 2026-01-15
Burien DADU Builders — Detached ADU Cost, Permits & Timeline
Burien has aligned with HB 1337 and is one of the more affordable King County ADU markets directly south of Seattle. A DADU is a standalone backyard cottage on the same lot as the main house — separate roof, separate entry, full kitchen and bath. Burien permits detached adu (dadu) on most single-family lots under its current code. DADUs on flat Boulevard Park and Gregory Heights lots, garage conversions in Old Burien core, and AADUs above existing garages.
SPEC_C.01 / ZONING — Burien, King County
Is a dadu allowed in Burien?
Burien allows detached ADU (DADU) on single-family lots (up to 1,000 sf), no owner-occupancy requirement, and no off-street parking required near transit.
- Max ADU size
- 1,000 sf (verify against city code)
- Parking
- No off-street parking required within ½-mile of major transit per HB 1337; otherwise city standard parking rules apply.
- Owner-occupancy
- Not required
- Height
- DADU heights commonly 18–24 ft per BMC Title 19; verify zone-specific overlays.
- Setbacks
- 5 ft side/rear typical for DADUs; primary-structure setbacks for AADUs.
- Lot coverage
- Lot coverage varies by RS-7.2 / RS-12 / RM zones; verify per parcel.
- Minimum lot size
- No explicit minimum lot size under HB 1337 alignment; functional minimums driven by setbacks.
- Tree retention
- Tree-retention applies above thresholds; mature stands in Gregory Heights and Seahurst trigger arborist review.
- Critical areas
- Coastal bluff geotech is the dominant constraint west of 1st Ave S; airport noise overlays apply on the north end.
- Alley access
- Alleys uncommon outside Old Burien core; most DADUs driveway-loaded.
Feasibility blockers to map early
- coastal bluff (Three Tree Point, Seahurst)
- steep slope
- airport noise overlay (north end)
- Coastal bluff geotech is the dominant constraint west of 1st Ave S; airport noise overlays apply on the north end.
- Tree-retention applies above thresholds; mature stands in Gregory Heights and Seahurst trigger arborist review.
SPEC_C.02 / PERMIT — Burien Community Development
Burien dadu permit timeline
Plan review (typical)
8–20 weeks
Burien Community Development standard ADU intake via MyBuildingPermit.
With one correction cycle
10–28 weeks
Includes one typical correction cycle.
Permit difficulty
5/10
Higher = more plan-check + design-review friction.
Documents you'll submit
- Site plan with parcel dimensions, structures, setbacks, and tree retention
- Architectural plans (floor plans, elevations, sections)
- Structural plans stamped by a WA-licensed engineer where required
- WSEC energy compliance worksheet
- Stormwater / drainage review per city threshold
- Utility plan (sewer / water / electric)
- DADU site plan showing separation from primary structure and any easements
- Independent utility connections (sewer, water, electric) or shared-service detail
Common plan-check corrections
- Setback or lot-coverage encroachment on site plan
- Energy-code U-value / glazing percentage mismatch
- Missing structural calcs for shear walls or beams
- Stormwater BMP not selected or sized for the impervious area
- Tree retention plan missing or critical-root-zone fencing not shown
- Setback or coverage error on detached structure
- Stormwater BMP missing for added impervious
Inspection sequence
- 01Foundation / footing
- 02Underfloor framing & insulation
- 03Rough-in: framing, mechanical, plumbing, electrical
- 04Insulation & vapor barrier
- 05Drywall / wallboard
- 06Final building, plumbing, mechanical, electrical
- 07Certificate of occupancy / final approval
Why Burien reviews can slow
- bluff geotech on west-side parcels
- airport noise mitigation reviews
- older septic-to-sewer conversions
SPEC_C.03 / COST — Burien cost tier 4/5
Burien dadu cost range
$260k–$484k · typical $353k
Drivers: site access, foundation, utility upgrades, and finish level.
What moves your number
- Foundation type (slab vs stepped)
- Crane / site access
- Sewer routing length
- Finish level
Utility & site notes for this city
- 200A panel upgrades common; PSE service coordination 2–4 weeks. Some unincorporated-historic parcels remain on septic.
- Panel upgrades typically $4–7k including PSE meter swap.
- Service split across multiple utility districts; confirm provider (Southwest Suburban / Lakehaven / Highline) per parcel before design.
- Bluff shoring and stepped foundations can add $25–60k on west-side view lots.
Ranges reflect typical 2026 project budgets and exclude land. Your exact cost depends on site access, foundation, utility upgrades, finish level, and city review depth — confirm with a feasibility study before committing.
SPEC_C.04 / TIMELINE — typical end-to-end ~60 weeks
Burien dadu schedule, phase by phase
- 01FeasibilityParcel + zoning + utility verification.1–4 weeks
- 02DesignSchematic → permit-ready set.4–12 weeks
- 03EngineeringStructural runs in parallel with design.2–6 weeks
- 04Permit reviewBurien Community Development standard ADU intake via MyBuildingPermit.8–20 weeks
- 05Corrections & resubmittalCycle depends on correction depth.2–8 weeks
- 06ConstructionDetached scope; conversions sit at the lower end.18–38 weeks
- 07Final sign-offFinal inspections and certificate of occupancy.1–4 weeks
Burien-specific delay risks · bluff geotech on west-side parcels · airport noise mitigation reviews · older septic-to-sewer conversions
Weather note · Excavation, foundations, and exterior weatherization sequence best Apr–Oct; framing and finishes continue year-round under temporary weather protection.
SPEC_C.05 / COMPARE — DADU vs the other ADU types in Burien
Why pick a dadu over the alternatives in Burien?
| vs. | Cost | Speed | Privacy | Resale | Best when |
|---|---|---|---|---|---|
| AADU | Higher — full new foundation + envelope. | Slower — ground-up build. | Better — no shared walls. | Strongest resale separation. | Backyard space + alley/side access available. |
| Garage Conversion | Higher — no reused shell. | Slower — full new structure. | Better — siting flexibility. | Higher — true second dwelling. | Lot can absorb a new footprint. |
| Basement ADU | Higher — no reused shell. | Slower — full new structure. | Much better — separate building. | Higher — visible second unit. | You want a true backyard cottage, not a downstairs unit. |
SPEC_C.06 / FIT — Is a dadu right for your Burien lot?
Best-fit profile for a Burien dadu
Pick a DADU when privacy, long-term rentability, and resale value matter more than speed or lowest cost. Avoid it on very tight lots, lots with deep critical-area buffers, or sites with no alley access and a long sewer run.
- Rental income
- Strongest of the four for long-term rental income — full privacy, full appliance set, dedicated yard space and parking when allowed.
- Aging parents / multigen
- Excellent for aging parents who want independence with proximity — single-level layouts with no shared walls or stairs.
- Tight lot
- Hardest of the four on a tight lot — DADU footprint plus required setbacks and tree retention can consume most rear-yard space.
- Alley access
- Ideal when alley access exists — separate guest entry, easier construction staging, and cleaner utility tie-ins.
- Lower budget
- Highest baseline budget of the four — foundation, framing, roof, siding, and full MEP are all new.
- Privacy
- Best privacy of all four — no shared walls, no shared entry, no shared mechanical chase.
- Speed to occupancy
- Slowest of the four — full ground-up build, full inspection sequence, full weather exposure during framing.
- Utilities already nearby
- Sewer routing length and side-sewer condition drive a meaningful share of the budget.
SPEC_C.07 / SOURCES — verified .gov / city / state references
Official sources for Burien ADU rules
- Burien Community DevelopmentPermit authority for Burien ADUs.
- Burien ADU informationADU permit rules under Burien Municipal Code Title 19.
- MyBuildingPermit.comShared permit portal Burien uses for ADU intake.
- Burien Municipal Code Title 19 — ZoningBMC zoning chapters covering ADU dimensional standards.
- RCW 36.70A.681 — Accessory Dwelling UnitsState law setting the floor for ADU regulations cities must meet.
- HB 1337 (2023) — Bill textAuthoritative text of the 2023 ADU reform: two ADUs per lot, 1,000 sf min, no owner-occupancy, parking limits near transit.
- WA Department of Commerce — ADU resourcesState guidance and model code for cities implementing HB 1337.
- WA State Energy Code (Residential)ADUs must meet WSEC; the residential provisions drive insulation, glazing, and HVAC requirements.
Burien DADU FAQ
Does Burien allow two ADUs per lot?
Yes — under HB 1337 alignment Burien permits one AADU and one DADU on most single-family lots.
How big can my Burien DADU be?
Up to 1,000 sf of gross floor area under the HB 1337 statewide floor.
Are west-side bluff lots feasible for a DADU?
Yes with proper geotech. Plan for stepped foundations, shoring, and limited construction-equipment access on tight bluff-top parcels.
Go deeper: Read the DADU vs AADU in Puget Sound: which to build (2026) guide
Which sewer district serves my Burien lot?
Burien is split across Southwest Suburban, Lakehaven, and Highline. Confirm the provider with a side-sewer card before design — it changes utility cost meaningfully.
Do I need a separate sewer line for a DADU?
Not always. Most Puget Sound cities allow a shared side-sewer with a cleanout and an as-built that proves capacity. A separate line is required only when the existing line is undersized, in failing condition, or the city explicitly demands one.
Can I rent the DADU short-term?
Short-term rental rules are city-specific and change. Seattle, Bellevue, Tacoma and most Tier-1 cities allow long-term rentals; short-term (STR) usually requires a separate license, an owner-occupancy attestation, or both. Confirm with the city before underwriting an STR pro forma.
How big can a DADU be in Washington?
HB 1337 sets a statewide floor of at least 1,000 sq ft of allowed gross floor area for an ADU. Individual cities may allow more (Seattle and Bellevue both go above 1,000 sf on many lots), but the city's specific max controls — always verify against the linked municipal code.
Go deeper: Read the DADU vs AADU in Puget Sound: which to build (2026) guide
What kind of foundation does a DADU need?
A stem-wall foundation on continuous footings is most common in the Puget Sound, with stepped foundations on sloped sites. Pin or pier foundations are sometimes used on tree-protection lots to limit critical-root-zone disturbance, but they require engineering.
Go deeper: Read the Foundation inspection checklist for Puget Sound homes guide
Other ADU types in Burien
Same dadu in nearby cities
SPEC_C.08 / NEXT
Plan your Burien dadu the right way
A 45-minute feasibility call confirms zoning, utility, and budget reality before you spend on design. Golden State ADU has been licensed in Washington since 2012 (LIC SEATTI*752N6).
More for Burien dadu planning
INTERNAL_LINKS / Deep Map