SPEC_C / KENT · DADU · Verified 2026-01-15
Kent DADU Builders — Detached ADU Cost, Permits & Timeline
Kent has aligned with HB 1337 and is one of the easier permit pathways on the south end of King County. A DADU is a standalone backyard cottage on the same lot as the main house — separate roof, separate entry, full kitchen and bath. Kent permits detached adu (dadu) on most single-family lots under its current code. DADUs on flat East Hill plateau lots, garage conversions in older Kent core, and AADUs above existing structures.
SPEC_C.01 / ZONING — Kent, King County
Is a dadu allowed in Kent?
Kent 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
- DADUs commonly capped near 24 ft per KCC 15.08.350.
- Setbacks
- 5 ft side/rear typical for DADUs; primary-structure setbacks for AADUs.
- Lot coverage
- Lot coverage typically 40% in most SF zones; verify per parcel.
- Minimum lot size
- No explicit minimum lot size; functional minimums dominate.
- Tree retention
- Tree-retention applies above thresholds; mature trees in East Hill add arborist review.
- Critical areas
- Valley-floor lots carry liquefaction risk; East Hill adds slope on the plateau edge.
- Alley access
- Alleys uncommon outside older Kent core.
Feasibility blockers to map early
- liquefaction (Kent Valley floor)
- settlement on filled lots
- East Hill plateau slope
- Valley-floor lots carry liquefaction risk; East Hill adds slope on the plateau edge.
- Tree-retention applies above thresholds; mature trees in East Hill add arborist review.
SPEC_C.02 / PERMIT — Kent Permit Center
Kent dadu permit timeline
Plan review (typical)
8–18 weeks
Kent Permit Center standard ADU intake via MyBuildingPermit.
With one correction cycle
10–26 weeks
Includes one typical correction cycle.
Permit difficulty
4/10
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 Kent reviews can slow
- valley-floor geotech & deep foundations
- side-sewer capacity on older valley laterals
- plateau slope on East Hill
SPEC_C.03 / COST — Kent cost tier 3/5
Kent dadu cost range
$246k–$458k · typical $334k
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
- Panel upgrades to 200A common; Puget Sound Energy or Tacoma Power depending on parcel location.
- Panel upgrades typically $4–7k.
- Kent has aggressive stormwater BMP requirements on valley-floor parcels; flow-control may be required at modest impervious thresholds.
- Deep foundations on liquefaction parcels can add $20–60k; East Hill slope can add $15–40k.
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 ~58 weeks
Kent 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 reviewKent Permit Center standard ADU intake via MyBuildingPermit.8–18 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
Kent-specific delay risks · valley-floor geotech & deep foundations · side-sewer capacity on older valley laterals · plateau slope on East Hill
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 Kent
Why pick a dadu over the alternatives in Kent?
| 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 Kent lot?
Best-fit profile for a Kent 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 Kent ADU rules
- Kent Permit CenterPermit authority for Kent ADUs.
- Kent ADU infoADU permit page and application requirements.
- MyBuildingPermit.comKent participates in the shared regional permit portal.
- 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.
Kent DADU FAQ
Does Kent allow two ADUs per lot?
Yes — under HB 1337 alignment, one AADU and one DADU are permitted on single-family lots.
How big can my Kent DADU be?
Up to 1,000 sf of gross floor area.
Will I need a sewer upgrade for my Kent ADU?
Older laterals in central Kent often need replacement when fixtures are added. A side-sewer card from the city clarifies capacity quickly.
Are East Hill lots good for DADUs?
Yes — flat plateau lots are some of the easiest detached-ADU sites in south King County, slope-edge lots aside.
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 Kent
Same dadu in nearby cities
SPEC_C.08 / NEXT
Plan your Kent 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 Kent dadu planning
INTERNAL_LINKS / Deep Map