Bothell vs. Lynnwood ADU rules
Bothell is the bigger build: ADUs top out at 1,200 sq ft versus Lynnwood's 1,000 sq ft cap (added to Lynnwood's code only in November 2025). Bothell also caps ADU impact fees at half of whatever the principal unit's fee would be (BMC 12.14.135(G)), a concrete break that Lynnwood's file doesn't offer — its own 2025 fee schedule is still unverified. Bothell additionally provides an amnesty path to legalize an old unpermitted ADU through inspection, something Lynnwood's code doesn't address. Both cities require zero parking for a conforming ADU and no owner-occupancy — those aren't the deciding factors here; the money and the square footage are.
✓ Verified against code · August 19, 2026
Bothell rules run under BMC 12.14.135 (Bothell Municipal Code), adopted by Ordinance 2415 (amended by Ords 2445, 2461), in effect since March 5, 2024.
✓ Verified against code · August 19, 2026
Lynnwood rules run under LMC Title 8 (Unified Development Code) — no standalone ADU section, adopted by Ordinance 3481 (amended by Ords 3492, 3507), in effect since July 1, 2025.
Rule by rule
| Rule | Bothell | Lynnwood |
|---|---|---|
| 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) | No ADU-specific cap — the units-per-lot rules govern: RN zones allow 3 units per lot base (a house plus two ADUs), 4 with one affordable unit or within a quarter-mile walk of a major transit stop. ADUs are a permitted use in the RN, RM-45, NC, and CDM zones.LMC 8.30 Table 8.30.03; Table 8.35.01 |
| 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) | 1,000 sq ft — written into the ADU definition itself (a cap added by Ord 3492 in November 2025; the original UDC had none). No garage or storage exclusion is stated.LMC 8.99.0250 (Ord 3492 §18) |
| 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 | No ADU-specific limit — a proposed 24-ft ADU cap was dropped at adoption. Detached units fall under the RN detached-configuration maximum of 35 ft.LMC 8.30 building-form tables |
| 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 | RN detached configuration: 10 ft from the street, 5 ft interior side and rear, 10 ft between buildings. No reduced alley setback — but where an alley exists, vehicle access must come from it.LMC 8.30 Tables 8.30.04–05 |
| 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) | Zero. Dwelling units under 1,200 sq ft of gross floor area require no parking — which covers every conforming ADU, citywide, with no transit test.LMC 8.40.0720(A); Table 8.40.70 |
| 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 | None — no owner-occupancy requirement exists anywhere in the adopted UDC. (Pre-UDC city guides described one; they're obsolete.)LMC Title 8 (verified absence) |
| 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) | RN zones use FAR by unit count — 0.6 for one unit, 0.8 for two, 1.0 for three, 1.2 for four — plus building-footprint standards instead of lot coverage, and required amenity space (shared 10% of the lot or 120 sq ft private per unit at grade).LMC 8.30 building-form tables |
| 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) | An ADU Permit is a Type 1a ministerial decision processed with the building permit — no notice, no hearing. Completeness review within 28 days; no codified final-decision deadline.LMC 8.90.0330; 8.90.0320 |
Bothell: 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.
Bothell: 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.
Lynnwood: worth knowing
- A pre-approved DADU plan program is in development — the designer-submission window closed July 2, 2026, but no plan sets are published yet.
- A proposed fire-sprinkler mandate for DADUs was rejected at adoption — it is not in the code.
- Edge case worth knowing: because ADUs count toward the 3-base/4-max units per lot, a lot that already holds two or more principal units can't always add two ADUs — a point of tension with the state statute's 'two ADUs per lot' that the city hasn't addressed publicly.
- Cleanup ordinances keep amending Title 8 (two in late 2025–2026 so far) — expect continued drift.
Lynnwood: on our watchlist
Pre-approved DADU plan sets pending publication (submissions closed July 2026).
Ongoing UDC cleanup ordinances (Ords 3492, 3507, 3508 so far) keep amending Title 8 — we re-check the ADU-relevant tables each pass.
The draft fee schedule listed a $640 ADU permit fee; the adopted fee schedule is unverified.
Full detail: Bothell · Lynnwood · back to the Washington hub. 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.