SPEC_C / BOTHELL · GARAGE CONVERSION · Verified 2026-01-15
Bothell Garage Conversion ADU — Cost, Permits & Code Upgrades
Bothell straddles King and Snohomish counties and has aligned with HB 1337 in both. A garage conversion ADU reuses an existing detached or attached garage shell as a legal dwelling unit — frequently the fastest and lowest-cost path to a permitted ADU in the Puget Sound. Bothell permits garage conversion adu on most single-family lots under its current code. DADUs on flatter plateau lots, basement conversions in modern subdivisions, and AADUs above garages.
SPEC_C.01 / ZONING — Bothell, King/Snohomish County
Is a garage conversion allowed in Bothell?
Bothell allows garage conversion 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 per BMC 12; commonly 24 ft.
- Setbacks
- 5 ft side/rear typical for DADUs.
- Lot coverage
- Coverage per BMC zone.
- Minimum lot size
- No explicit ADU minimum lot size under current BMC.
- Tree retention
- Tree-retention per BMC applies above thresholds.
- Critical areas
- North Creek riparian buffers and canyon slope.
- Alley access
- Limited alleys; most lots front-load.
Feasibility blockers to map early
- North Creek stream buffers
- hillside lots above the canyon
- split county jurisdiction
- North Creek riparian buffers and canyon slope.
- Tree-retention per BMC applies above thresholds.
SPEC_C.02 / PERMIT — Bothell Community Development
Bothell garage conversion permit timeline
Plan review (typical)
8–20 weeks
Bothell 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)
- Existing-conditions plan with as-built slab elevations and framing
- Foundation upgrade detail to bring perimeter up to current code
- Envelope retrofit detail for insulation and weather barrier compliance
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
- Existing slab not verified for habitable use
- Envelope U-value below current WSEC requirement
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 Bothell reviews can slow
- North Creek buffers
- hillside geotech
- King vs Snohomish coordination on jurisdiction-split projects
SPEC_C.03 / COST — Bothell cost tier 4/5
Bothell garage conversion cost range
$126k–$281k · typical $194k
Slab + framing reuse vs full envelope rebuild drives the range.
What moves your number
- Existing slab condition
- Perimeter foundation upgrade
- Envelope retrofit depth
- Plumbing routing
Utility & site notes for this city
- PSE coordination standard; modern Bothell subdivisions usually have panel capacity.
- Panel upgrades typically $5–8k when needed.
- Northshore Utility District; side-sewer review required.
- Canyon-edge geotech and crane access add $15–50k on affected parcels.
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
Bothell garage conversion 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 reviewBothell 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
Bothell-specific delay risks · North Creek buffers · hillside geotech · King vs Snohomish coordination on jurisdiction-split projects
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 — Garage Conversion vs the other ADU types in Bothell
Why pick a garage conversion over the alternatives in Bothell?
| vs. | Cost | Speed | Privacy | Resale | Best when |
|---|---|---|---|---|---|
| DADU | Lower — reused shell. | Faster — no new framing. | Comparable — often detached. | Slightly lower — smaller, lower ceilings typical. | Existing garage is sound and large enough. |
| AADU | Similar. | Similar. | Higher when garage is detached. | Comparable. | Garage is detached or has alley access. |
| Basement ADU | Often lower — fewer waterproofing risks. | Faster — drier, more accessible. | Higher when detached. | Comparable. | You'd rather not occupy the main-house basement. |
SPEC_C.06 / FIT — Is a garage conversion right for your Bothell lot?
Best-fit profile for a Bothell garage conversion
Pick a garage conversion when an existing garage is structurally sound, has workable ceiling height, and the city accepts the existing slab. Avoid it when the slab is cracked, the foundation is shallow, or the envelope cannot reach current WSEC numbers without taking the shell apart.
- Rental income
- Good for long-term rental in the right neighborhood — usually under 600 sf of livable area, which fits 1-bedroom market demand.
- Aging parents / multigen
- Good when the garage is single-level, has alley access, and can be brought to ADA-adjacent standards.
- Tight lot
- Best of the four when no new footprint is acceptable — the structure already exists.
- Alley access
- Excellent — most detached garages already face an alley with utilities nearby.
- Lower budget
- Lowest baseline budget of the four when the existing shell is sound.
- Privacy
- Strong if detached; weaker if the garage is attached to the main house.
- Speed to occupancy
- Fastest of the four when no foundation upgrade is required.
- Utilities already nearby
- Often the strongest fit — existing electrical, frequently existing water rough-in.
SPEC_C.07 / SOURCES — verified .gov / city / state references
Official sources for Bothell ADU rules
- Bothell Community DevelopmentPermit authority for Bothell ADUs.
- Bothell ADU infoCity landing page — confirm current ADU path on visit.
- MyBuildingPermit.comPermit intake for Bothell.
- 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.
Bothell Garage Conversion FAQ
Does Bothell allow two ADUs per lot?
Yes — under HB 1337 alignment in both King and Snohomish portions of the city.
Is owner-occupancy required in Bothell?
No. The requirement was removed to align with state law.
Which county handles my Bothell ADU permit?
Bothell handles the permit citywide regardless of county; some downstream tax and utility rules differ by county.
How long does Bothell ADU permit review take?
Standard ADU reviews run 8–20 weeks.
Will my existing garage slab pass code?
Often yes for an at-grade conversion, but the slab must be verified for vapor, depth, and (for additions of mass) bearing. A 4-inch slab over compacted base with a vapor retarder is the common minimum; older slabs sometimes need an overlay or a topping pour.
Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide
Do I have to keep the garage door?
No. Most cities require infilling the garage door opening with a framed wall and code-compliant insulation and finish. A few preserve the visual rhythm of the streetscape by requiring carriage-style cladding — confirm in design review where applicable.
Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide
Can I add a second story above the converted garage?
Sometimes — but a second story usually means a new foundation, new shear walls, and new framing. At that scope, a new DADU is often the better answer than overloading an old garage shell.
Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide
What if my garage has no plumbing?
Plumbing can be added, but the routing cost and the cost of breaking the slab to lay drain lines is one of the bigger variables in a garage conversion. Bring a plumber to the feasibility walk.
Go deeper: Read the Garage conversion timeline in Puget Sound (2026) guide
Other ADU types in Bothell
SPEC_C.08 / NEXT
Plan your Bothell garage conversion 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 Bothell garage conversion planning
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