ADUs & DADUs in Bothell
The Svensen Timber Collection — productized, priced, ready.
Bothell’s revitalized downtown and the Sammamish River corridor have made it one of the most desirable spots on the county line. We build custom homes, additions, and ADUs that fit both its established neighborhoods and its new energy.
Washington's ADU law changes turned the backyard into the most valuable square footage on many lots. Svensen builds detached (DADU) and attached (ADU) dwellings that add real, rentable, livable space — with the same timber craft as our custom homes.
To make the decision simple, we productized it. The Svensen Timber Collection is a set of fixed models with tiered pricing, so you know what you are getting and what it costs before the first drawing.
The Svensen Timber Collection
- Timber 800 — efficient one-bed / studio footprint
- Timber 1000 — one to two bedrooms, full kitchen
- Timber 1200 — two-plus bedrooms, premium finish
- Detached (DADU) and attached (ADU) configurations
- Permit and code navigation under current WA ADU law
- Site work, utility connections, and finish
Bothell allows more than anywhere else we build
Bothell has the most generous accessory dwelling unit rules in our service area, and they are current rather than pending. An accessory unit can be built up to 1,200 square feet, which is above the state floor of 1,000. A conversion of existing space can exceed even that with director approval, provided it stays within 40 percent of the primary dwelling’s gross floor area.
Height is unusually generous too. A detached unit can reach 30 feet, or 33 feet where it sits over an existing accessory structure. Detached units are also exempt from the rule that otherwise caps accessory buildings at five percent of lot area, which is what makes a genuinely full-size cottage possible here.
Two provisions are worth knowing because neighbouring cities go the other way. One accessory unit is allowed on a lot developed with middle housing. And one accessory unit is allowed on lots designated with critical areas or their buffers, where Marysville, for instance, excludes critical-area portions of a lot entirely.
- Size
- Up to 1,200 sq ft. Conversions may exceed that with director approval, within 40% of the primary dwelling.
- Height
- Detached units up to 30 feet, or 33 feet over an existing accessory structure.
- Lot coverage
- Detached accessory dwelling units are exempt from the 5% accessory-building coverage limit.
- Middle housing
- One accessory unit is allowed on a lot developed with middle housing.
- Critical areas
- One accessory unit is allowed on lots designated with critical areas or their buffers.
- Existing unpermitted units
- There is a route to approval. The owner applies, and where no building permit was issued the city requires a structural inspection, covered by the application fee.
- Impact fees
- Capped at 50% of what the principal unit would pay. Traffic, fire and park impact fees apply at issuance.
- Septic lots
- King County Health or Snohomish Health District approval is required when on septic and adding square footage or bedrooms.
Source: Bothell Municipal Code 12.14.135, verified September 2026. Codes and fee schedules change. Confirm current requirements with the city before relying on this.
Because we mill and engineer in-house, a productized ADU does not mean a cheap one. The Timber Collection ships with real exposed timber that a typical modular or panelized ADU cannot offer at the price.
How the supply chain worksTiered, transparent pricing
Timber 800 / 1000 / 1200 are offered as priced tiers. Pick a model, confirm your site, and we give you a number — no mystery, no open-ended bid. (Current tier pricing available on request.)
From idea to backyard build
Pick a model
Choose the Timber 800, 1000, or 1200 based on your goals and lot.
Confirm the site
We assess setbacks, utilities, and access, and confirm your build is permittable.
Permit & prepare
We handle the ADU permit path and prep the site.
Build & finish
Your unit is built, connected, and finished to the Collection standard.
ADUs & DADUs in Bothell: FAQ
Can I build an ADU or DADU in Bothell?
In most cases, yes. Washington’s 2024–2025 ADU law changes (HB 1337) and Snohomish County’s Ordinance 25-014 expanded ADU rights, allowing up to two units on many lots. We confirm what your specific Bothell lot allows during feasibility.
How much does an ADU cost in Bothell?
Detached ADUs in the Puget Sound typically run roughly $250K–$450K all-in as of 2025. Our Svensen Timber Collection (Timber 800, 1000, 1200) is offered as fixed tiers so you get a clear Bothell number up front instead of an open-ended bid.
How big can my ADU be in Bothell?
Most Washington jurisdictions allow ADUs in the 800–1,200 sq ft range, which is exactly why our Timber Collection comes in 800, 1000, and 1200 — sized to the rules and ready for your Bothell backyard.
How big can an ADU be in Bothell?
Up to 1,200 square feet, which is larger than the state floor and larger than most neighbouring cities allow. A conversion of existing space can go beyond that with the community development director’s approval, as long as it stays within 40 percent of the primary dwelling’s gross floor area. Bothell is the easiest city in our area to build a genuinely full-size cottage in.
My lot has a wetland buffer. Am I out of luck?
Not in Bothell. One accessory dwelling unit is allowed on lots designated with critical areas or their buffers. That is the opposite of how some neighbouring cities handle it, so a lot that would be unworkable a few miles north may be fine here. The buffer still constrains where the unit sits, which is a design question rather than a permission one.
How tall can a detached unit be?
Up to 30 feet, or 33 feet where it sits over an existing accessory structure. That is well above the state minimum and it opens up options, including a unit above a garage with proper ceiling height rather than a cramped loft.
There is already an apartment in my basement that was never permitted. What now?
Bothell has a defined route. You apply to the city for approval, and where the space was created without a building permit the city requires an inspection to confirm the structure is sound and meets requirements. The application fee covers that inspection. It is a far better position than discovering the problem during a sale.
Does it matter which county my Bothell property is in?
For some things, yes. Bothell straddles the King and Snohomish county line, and if your property is on septic and you are adding square footage or bedrooms you will need approval from King County Health or the Snohomish Health District depending on which side you are on. Worth identifying early, because it affects the submittal package.
ADUs & DADUs nearby
Let’s build something that outlasts the mortgage.
Tell us about your project. We’ll tell you what’s buildable, what it costs, and how the supply chain works in your favor.