Bothell DADU Size Limits: Can You Build 1,200 Sq Ft?
Bothell’s current ADU section allows a unit up to 1,200 square feet. Its detached-unit height limit is 30 feet, or 33 feet over an existing accessory structure. The allowable unit count has separate provisions for middle-housing and critical-area lots.
Sources checked November 5, 2026. Confirm the requirements for your parcel with its permitting authority.
What does the current Bothell code allow?
| BMC 12.14.135 topic | Published rule |
|---|---|
| Ordinary ADU size | Up to 1,200 sq ft. |
| Detached height | Up to 30 ft. |
| Above an existing accessory structure | Up to 33 ft. |
| Ordinary unit count | Two ADUs per lot, with separate exceptions. |
The live code is current through Ordinance 2488, passed September 15, 2026. Older summaries that describe an 800-square-foot limit or lower heights should not be used as the starting point for a new proposal.
Official guidance: Bothell BMC 12.14.135: accessory dwelling units.
When does the unit-count answer change?
The ADU section allows one ADU on a lot developed with middle housing and one on a lot designated with critical areas or buffers. It also contains a provision for conversions exceeding the ordinary size limit, subject to the stated approval and floor-area condition.
Establish the existing development and mapped designation before counting potential units. The ordinary allowance is not a substitute for reviewing the exception that applies to the actual property.
Official guidance: Bothell BMC 12.14.135: accessory dwelling units.
Does a larger allowance mean the footprint fits?
Draw the proposed floor area on the site with the principal home, access, outdoor areas and services. Then test the applicable setbacks, coverage and other development requirements. The size limit is one input to the layout, not a parcel-specific building envelope.
Compare a single-story and a smaller-footprint two-story arrangement against the household’s priorities. Consider stairs, daylight and the connection to the main house. A height allowance does not establish that either arrangement is the better design.
What information makes the first consultation useful?
- A current parcel record and available site plan.
- Existing dwelling and accessory-building information.
- The intended cottage floor area and number of units.
- Known critical-area information and the initial service approach.
Bring those records to a free TimberworX consultation. Detailed design and budgeting are paid preconstruction work. Use the permit guide below to identify the documents that move the selected concept toward review.
A few things to know
Is 1,000 square feet the universal Eastside DADU cap?
No. Bothell’s current ADU section lists up to 1,200 square feet.
Does the standard two-ADU allowance apply to all Bothell lots?
The code has separate middle-housing and critical-area provisions. Check the actual lot.
Keep planning
Bothell DADU Permits: Documents, Utilities and Fees
Bothell’s DADU application needs address assignment, utility availability and fire-flow information. See the permit sequence and 2026 fee categories.
DADU setbacks, height and lot coverage
Understand DADU property-line setbacks, building height, lot coverage and the site conditions that shape your backyard home.
DADU or home addition: which fits your plans?
Compare a detached backyard home with a home addition around household use, privacy, site work and the complete project scope.