SPEC_C / BURIEN · BASEMENT ADU · Verified 2026-01-15
Burien Basement ADU — Egress, Ceiling Height, Cost & Permits
Burien has aligned with HB 1337 and is one of the more affordable King County ADU markets directly south of Seattle. A basement ADU is a self-contained dwelling carved out of the main house's existing basement — independent entry, kitchen, bath, with code-required egress and fire separation. Burien permits basement adu 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 basement adu allowed in Burien?
Burien allows basement ADU 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 basement adu 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)
- Egress window detail meeting current IRC sizing
- Ceiling height verification across each room
- Fire-separation and dwelling-unit separation 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
- Egress window undersized
- Ceiling height below 7 ft in habitable area
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 basement adu cost range
$140k–$316k · typical $214k
Egress, ceiling height, and waterproofing dominate.
What moves your number
- Egress window cuts
- Ceiling height workability
- Waterproofing scope
- Plumbing & fire separation
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 ~56 weeks
Burien basement adu 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.12–32 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 — Basement ADU vs the other ADU types in Burien
Why pick a basement adu over the alternatives in Burien?
| vs. | Cost | Speed | Privacy | Resale | Best when |
|---|---|---|---|---|---|
| DADU | Lower — reused shell. | Faster — interior work. | Lower — same building. | Lower — invisible second unit. | Existing basement is dry and tall enough. |
| AADU | Similar — often lower if egress already exists. | Similar. | Comparable. | Comparable. | You want a unit below grade, not as a side addition. |
| Garage Conversion | Often higher — egress cuts + waterproofing. | Comparable. | Lower — attached to main house. | Lower — counts as basement, not separate structure. | No usable garage exists. |
SPEC_C.06 / FIT — Is a basement adu right for your Burien lot?
Best-fit profile for a Burien basement adu
Pick a basement ADU when ceiling height and egress already meet code, and the basement is dry. Avoid it when you'd have to underpin the foundation just to reach ceiling height — at that scope, an AADU addition or a DADU is usually a better answer.
- Rental income
- Good for long-term rental — typically a 1-bedroom configuration aimed at single tenants or couples.
- Aging parents / multigen
- Limited — stair access to the main house can be a hard blocker for mobility-restricted occupants.
- Tight lot
- Best of the four on a tight lot — zero new footprint.
- Alley access
- Less relevant — entry is usually street-side or side-yard.
- Lower budget
- Often the lowest of the four when egress and ceiling height already work.
- Privacy
- Moderate — separate entry helps, but tenant lives below the primary unit.
- Speed to occupancy
- Fast — interior work, minimal weather exposure, predictable inspection sequence.
- Utilities already nearby
- Strong — extends existing service rather than running new lines.
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 Basement ADU 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.
Is owner-occupancy required for a Burien ADU?
No. Burien removed the owner-occupancy requirement to align with state law.
How big can my Burien DADU be?
Up to 1,000 sf of gross floor area under the HB 1337 statewide floor.
How long does Burien ADU permit review take?
Standard reviews land in roughly 8–20 weeks; bluff geotech and noise overlays can add weeks.
What's the minimum ceiling height for a basement ADU?
The IRC minimum is 7 ft in habitable rooms, with allowable reductions under structural members. Some jurisdictions allow as low as 6 ft 8 in under beams or ductwork — but the room average must still meet code.
Do I have to add egress windows in every bedroom?
Yes. Every sleeping room below grade needs an egress window meeting current IRC sizing, with a window well sized and graded for emergency exit. This is one of the most common single-line items in a basement-ADU budget.
What if my basement has moisture issues?
Resolve them before drywall. Interior drainage, sump pump upgrades, exterior re-grading, and dehumidification are all viable strategies — but they need to be designed in, not bolted on after final inspection.
Can I rent the basement ADU without the upstairs being occupied?
Generally yes — HB 1337 removed owner-occupancy requirements in Tier-1 cities. Outside Tier-1, owner-occupancy may still apply; confirm against the city's adopted ADU code.
Other ADU types in Burien
Same basement adu in nearby cities
SPEC_C.08 / NEXT
Plan your Burien basement adu 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 basement adu planning
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