Bothell ADU rules
✓ Verified against code · August 19, 2026
Current rules under BMC 12.14.135 (Bothell Municipal Code), adopted by Ordinance 2415 (amended by Ords 2445, 2461), in effect since March 5, 2024. Bothell adopted its core ADU rewrite in March 2024, then kept going: a December 2024 amendment, and in July 2025 Ordinance 2461 repealed minimum off-street parking citywide and capped ADU impact fees at half the principal-unit rate. Its residential zones were also renamed in 2025 — older guides cite zone labels that no longer exist.
Common questions, answered from the code
Do I need parking for a Bothell ADU?
No — and not because of an ADU exception. Bothell repealed minimum off-street parking requirements citywide in 2025. Any source telling you an ADU needs a space is quoting the pre-2025 code.
BMC 12.16.030 (Ord 2461) · Permalink
How tall can a Bothell DADU be?
30 feet — or 33 feet when built above an existing accessory structure like a garage. That's a two-story unit with room to spare, and among the most generous DADU height allowances in Puget Sound.
BMC 12.14.135(E) · Permalink
What do impact fees cost on a Bothell ADU?
They're capped at half of whatever the principal unit's fee would be, under a 2025 amendment. Exact amounts depend on which county side of the city you're on.
BMC 12.14.135(G) · Permalink
How many ADUs can I build in Bothell?
Two per lot in any mix — with two exceptions: lots developed with middle housing get one, and lots constrained by critical areas or buffers get one.
BMC 12.14.135(A)–(C) · Permalink
I have an old unpermitted ADU — can I legalize it?
Yes. Bothell's code provides an amnesty path: apply, pass a building inspection, and the unit can be brought into compliance.
BMC 12.14.135(F) · Permalink
The rules at a glance
| ADUs allowed per lot | Two ADUs per lot, in any mix. Exceptions: one ADU on lots developed with middle housing, and one on lots constrained by critical areas or their buffers.BMC 12.14.135(A)–(C) |
| Maximum size | 1,200 sq ft. Conversions of existing space may exceed that with director approval, capped at 40% of the primary dwelling's gross floor area.BMC 12.14.135(D)(1)–(2) |
| Detached ADU height | 30 ft for a detached ADU — 33 ft when built over an existing accessory structure. (Other accessory buildings are capped at 20 ft.)BMC 12.14.135(E); 12.14.130 |
| Detached ADU setbacks | Side: 5 ft in all residential zones. Rear: a DADU matches the primary structure's rear setback (R-C 35 ft; R-L1/R-L2 15 ft; R-M1/R-M2 10 ft), except on alleys, where alley-structure standards apply (down to 0 ft at the alley line; vehicle access needs 25 ft clear to the alley's far edge).BMC 12.14.070(B); 12.14.030(A); 12.14.060 |
| Off-street parking | None. Bothell repealed minimum off-street parking citywide in 2025 — 'there is no required minimum number of off-street parking spaces.'BMC 12.16.030 (Ord 2461 §2, 2025) |
| Owner-occupancy | None. The pre-2024 code required owner or family occupancy more than six months a year plus a recorded covenant — all struck by Ordinance 2415.BMC 12.14.135 (current); Ord 2415 |
| Lot coverage / floor area | No FAR. Hard-surface coverage is capped by zone (35% in R-C up to 75% in R-M2). DADUs that meet the ADU size limit are exempt from the 5%-of-lot-area cap that binds other accessory buildings.BMC 12.14.030(A), (B)(8); 12.14.135(D)(2) |
| Permit path & timeline | Single-family building permit with the city's ADU submittal checklist — no separate land-use permit. No published review timeline. An amnesty path lets unpermitted existing ADUs be legalized through application and inspection.BMC 12.14.135(F); city handout 3f (rev. Dec 2025) |
Worth knowing
- Impact fees on ADUs are capped at 50% of the fee assessed on the principal unit (added 2025).
- The 30/33-ft DADU height allowance is among the most generous in the region.
- Bothell straddles King and Snohomish counties — county-side fees and utility districts differ across the city line.
- Residential zones were renamed in 2025 (R-L1/R-L2/R-M1–M4); guides citing the old zone labels predate the change.
- Middle-housing regulations are still actively moving (a 2026 ordinance amended them again) — the one-ADU-on-middle-housing-lots rule sits in amended territory.
On our watchlist
Ordinance O-2479 (2026) amended the middle-housing regulations (we verified it did not alter 12.14.135); the middle-housing interaction rules remain actively amended territory.
Check your parcel
The rules above are citywide — what you can build depends on your lot’s zone, size, and setbacks. Look yours up on the official viewers:
Primary sources
Other Washington cities
Bellevue · Burien · Edmonds · Everett · Issaquah · Kent · Kirkland · Lynnwood · Olympia · Redmond · Renton · Sammamish · Seattle · Shoreline · Tacoma
Not legal advice. Every fact above cites the code section it comes from — check the cite, or ask your city’s planning department to confirm your specific lot. Spotted an error or a new ordinance? See about to reach us; corrections are logged in the changelog.