An ADU builder in Bothell is a licensed contractor who designs and constructs accessory dwelling units — detached backyard units, garage conversions, attached additions, and junior ADUs (JADUs). Because an ADU is a complete second dwelling, the builder coordinates foundation, framing, plumbing, electrical, and HVAC work and pulls it through Bothell's permit process and utility connections. Not every general contractor has built one, so the right builder is one with ADU-specific experience in Washington.
What ADU Builders Cost in Bothell [17][18][19][20]
Based on our Bothell cost data, expect the following ranges from local ADU builders. Quotes for the same scope typically vary 20-40% between contractors, so getting at least three bids is the single best way to control cost.
| New Detached ADU (all-in) | $325,000-$550,000 |
| Cost per Sq Ft | $400-$650 |
| Garage Conversion | $100,000-$225,000 |
| Prefab / Modular ADU (installed) | $300,000-$450,000 |
| City Permit & Plan Review | 2026 fees: a valuation-based permit fee (Table 20.02.155-A: $1,514 plus $9 per $1,000 over $100,000), plan check at 65 percent, planning review $231, site review $834, energy review $230, plumbing and mechanical 16 percent, 5 percent tech fee. A $300,000 detached ADU: about $7,700 plus impact fees |
| Impact Fees | Four impact fees at permit issuance, each capped at 50 percent of the principal unit's (BMC 12.14.135(G); RCW 36.70A.681(1)(a)). 2026 rates (form X, updated April 2026): transportation $3,311 per ADU from May 1, 2026 (BMC 17.045.070; single-family $13,387) plus a 3 percent administrative fee; fire $232.30 ($229.34 sprinklered; BMC 21.16); park "50% of Principal Unit", i.e. $779-$2,005 against the $1,557.15-$4,009.85 house brackets (BMC 21.08); school $16,550 per single-family and $5,945 per multifamily unit from Jan 1, 2026 plus a $70 administrative fee (BMC 21.12), with no ADU row on the form. Roughly $4,400-$5,650 before any school fee. Impact fees do not vest: the rate in force at issuance applies |
For a full line-item breakdown, see our Bothell ADU cost guide. To confirm what you're allowed to build before you hire, review the Bothell ADU rules (max detached size: 1,200 sq ft: "An accessory dwelling unit may be developed up to 1,200 square feet" (BMC 12.14.135(D)(1)), 200 sq ft above the state floor (RCW 36.70A.681(1)(f)). A conversion of existing space may exceed 1,200 sq ft with the community development director's approval, up to 40 percent of the primary unit's gross floor area. Detached ADUs are exempt from the BMC 12.14.130 five-percent-of-lot cap on accessory buildings (BMC 12.14.135(D)(2)); hard surface coverage is the real limit; owner-occupancy: Not required. BMC 12.14.135, as codified through Ord. 2464 (Sept 16, 2025), has no owner-occupancy condition, rental restriction or covenant, and RCW 36.70A.681(1)(b) forbids one. State law also bars the city from blocking the separate sale of an ADU that has been made a condominium unit (RCW 36.70A.681(1)(k))).
Get Free ADU Quotes in Bothell
Tell us about your project and we'll pass it to ADU builders serving Bothell. Free, no obligation — you choose who to work with. We don't have builders in every area yet; if nobody covers yours, we'll email you to say so.
1. Tell us your project
Takes about a minute.
Takes about a minute.
2. We match local pros
Up to 5 independent local ADU builders — never more, and we tell them nothing you don't submit here.
Up to 5 independent local ADU builders — never more, and we tell them nothing you don't submit here.
3. You choose
Compare quotes, verify license & insurance, hire (or don't). No spam either way.
Compare quotes, verify license & insurance, hire (or don't). No spam either way.
🔒 Your info is secure. We share it only with contractors quoting your project. No spam, no obligation.
Just browsing? Search ADU builders near you by ZIP code.
How to Vet an ADU Builder in Bothell
- License: Confirm a current contractor's license in Washington and that it's in good standing. Ask for the license number and verify it with the state board.
- ADU-specific experience: Ask how many ADUs they've completed in or near Bothell and request addresses or photos. ADU permitting and setbacks differ from a kitchen remodel.
- Portfolio & references: Get references from recent ADU clients and, if possible, visit a finished unit.
- Insurance: Verify general liability and workers' compensation coverage. Ask for a certificate of insurance.
- Written, detailed bid: Insist on an itemized, fixed-price or clearly-scoped bid — not a verbal estimate. It should state whether permits (2026 fees: a valuation-based permit fee (Table 20.02.155-A: $1,514 plus $9 per $1,000 over $100,000), plan check at 65 percent, planning review $231, site review $834, energy review $230, plumbing and mechanical 16 percent, 5 percent tech fee. A $300,000 detached ADU: about $7,700 plus impact fees), plan check (Plan check fee is 65 percent of the building permit fee and is due at submittal. Plans are 24 by 36 inches maximum, construction drawings at 1/8 inch to the foot or larger. The site plan must show a hard surface coverage table per BMC 12.14.140(B), distances from every structure to the property lines, footing and roof drain routing and discharge, existing and proposed parking, 2-ft contours (5-ft where slope is 15 percent or more), easements, and any environmentally sensitive area on site, adjacent, or within 200 ft (wetlands, steep slopes, streams). That last item decides whether you get two ADUs or one under BMC 12.14.135(C). A new detached ADU needs the full Washington State Energy Code worksheets (prescriptive compliance, heating system size, glazing schedule)), and impact fees (Four impact fees at permit issuance, each capped at 50 percent of the principal unit's (BMC 12.14.135(G); RCW 36.70A.681(1)(a)). 2026 rates (form X, updated April 2026): transportation $3,311 per ADU from May 1, 2026 (BMC 17.045.070; single-family $13,387) plus a 3 percent administrative fee; fire $232.30 ($229.34 sprinklered; BMC 21.16); park "50% of Principal Unit", i.e. $779-$2,005 against the $1,557.15-$4,009.85 house brackets (BMC 21.08); school $16,550 per single-family and $5,945 per multifamily unit from Jan 1, 2026 plus a $70 administrative fee (BMC 21.12), with no ADU row on the form. Roughly $4,400-$5,650 before any school fee. Impact fees do not vest: the rate in force at issuance applies) are included.
- Permit handling: Confirm they manage Bothell's permit process ("A building permit filed online at MyBuildingPermit.com: Building, then Single Family Residential, then Activity Type, then Accessory Dwelling Unit (City of Bothell ADU submittal checklist, form 3f, updated Dec 2025). No conditional use permit, hearing, design review or covenant. Before you apply: an assigned address letter (form 54); if the City of Bothell is your water provider, a water and sewer availability certificate (form 36, up to two weeks); if Alderwood, Northshore or Woodinville is, their certificate and a fire-flow letter. King County Public Health or Snohomish Health District sign-off is needed if you are on septic and adding area or bedrooms. An ADU built without a permit can be legalized: apply, pass a building inspection covered by the ADU application fee, and meet BMC 12.14.135 and Title 20 (BMC 12.14.135(F)). The city may not require street improvements (RCW 36.70A.681(1)(l)). Bothell City Hall, 18415 101st Ave NE, 425-806-6400", typically Not published: the city's ADU checklist (form 3f, Dec 2025) gives no review time; ask Development Services at 425-806-6400. Add up to two weeks for the water and sewer availability certificate where the City is the provider, and get the address assignment first) and who is responsible if revisions are required.
- Payment schedule: Avoid large upfront payments. A reasonable schedule ties payments to completed milestones.
Questions to Ask Before You Hire
- How many ADUs have you built in Bothell in the last two years?
- Is your bid fixed-price, and what would trigger a change order?
- Are permits, plan check, and utility connection fees included?
- What's a realistic timeline, including permit review (Not published: the city's ADU checklist (form 3f, Dec 2025) gives no review time; ask Development Services at 425-806-6400. Add up to two weeks for the water and sewer availability certificate where the City is the provider, and get the address assignment first) and construction?
- Who is my point of contact and how are delays communicated?
- What warranty do you provide on workmanship?
- Can you share three recent Washington ADU client references?
Finance Your ADU Project
Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.
Some links on this page are affiliate links. We may earn a commission at no extra cost to you. Learn more
Are you an ADU builder? Get Bothell leads
Homeowners on this page submit real ADU project requests in Bothell. Each one goes to up to five local builders — that is what the homeowner agrees to — so claiming never takes it from anyone and there is no bidding. In practice far fewer ever make contact, which is why the number is five rather than three. A flat $50 only on the leads you accept: no subscription, no contract, and you deal with the homeowner directly.
Get Bothell ADU Leads →Frequently Asked Questions
How much do ADU builders charge in Bothell?
ADU builders in Bothell typically quote $325,000-$550,000 for a new detached unit, or about $400-$650 per square foot, including design, permitting, and construction. A garage conversion runs $100,000-$225,000 and a prefab/modular ADU averages $300,000-$450,000. Add city permit and plan-review fees (2026 fees: a valuation-based permit fee (Table 20.02.155-A: $1,514 plus $9 per $1,000 over $100,000), plan check at 65 percent, planning review $231, site review $834, energy review $230, plumbing and mechanical 16 percent, 5 percent tech fee. A $300,000 detached ADU: about $7,700 plus impact fees) plus impact fees of Four impact fees at permit issuance, each capped at 50 percent of the principal unit's (BMC 12.14.135(G); RCW 36.70A.681(1)(a)). 2026 rates (form X, updated April 2026): transportation $3,311 per ADU from May 1, 2026 (BMC 17.045.070; single-family $13,387) plus a 3 percent administrative fee; fire $232.30 ($229.34 sprinklered; BMC 21.16); park "50% of Principal Unit", i.e. $779-$2,005 against the $1,557.15-$4,009.85 house brackets (BMC 21.08); school $16,550 per single-family and $5,945 per multifamily unit from Jan 1, 2026 plus a $70 administrative fee (BMC 21.12), with no ADU row on the form. Roughly $4,400-$5,650 before any school fee. Impact fees do not vest: the rate in force at issuance applies. Quotes for the same scope commonly vary 20-40% between builders, so collect at least three bids.
How do I find a good ADU builder in Bothell?
Look for a licensed contractor with completed ADU projects in Bothell specifically — ADUs involve local zoning, setback rules, and utility connections that general remodelers may not have handled. Verify the license, ask for an ADU-specific portfolio and references, confirm they carry liability and workers' comp insurance, and get a written fixed-price or detailed bid. Submit a request below and we'll forward it to local ADU builders serving Bothell for free quotes.
Do ADU builders in Bothell handle permits?
Most full-service ADU builders manage the permit process for you. In Bothell the approval process is "A building permit filed online at MyBuildingPermit.com: Building, then Single Family Residential, then Activity Type, then Accessory Dwelling Unit (City of Bothell ADU submittal checklist, form 3f, updated Dec 2025). No conditional use permit, hearing, design review or covenant. Before you apply: an assigned address letter (form 54); if the City of Bothell is your water provider, a water and sewer availability certificate (form 36, up to two weeks); if Alderwood, Northshore or Woodinville is, their certificate and a fire-flow letter. King County Public Health or Snohomish Health District sign-off is needed if you are on septic and adding area or bedrooms. An ADU built without a permit can be legalized: apply, pass a building inspection covered by the ADU application fee, and meet BMC 12.14.135 and Title 20 (BMC 12.14.135(F)). The city may not require street improvements (RCW 36.70A.681(1)(l)). Bothell City Hall, 18415 101st Ave NE, 425-806-6400". Review time: not published: the city's ADU checklist (form 3f, Dec 2025) gives no review time; ask Development Services at 425-806-6400. Add up to two weeks for the water and sewer availability certificate where the City is the provider, and get the address assignment first. Confirm in writing whether permit fees, plan check (Plan check fee is 65 percent of the building permit fee and is due at submittal. Plans are 24 by 36 inches maximum, construction drawings at 1/8 inch to the foot or larger. The site plan must show a hard surface coverage table per BMC 12.14.140(B), distances from every structure to the property lines, footing and roof drain routing and discharge, existing and proposed parking, 2-ft contours (5-ft where slope is 15 percent or more), easements, and any environmentally sensitive area on site, adjacent, or within 200 ft (wetlands, steep slopes, streams). That last item decides whether you get two ADUs or one under BMC 12.14.135(C). A new detached ADU needs the full Washington State Energy Code worksheets (prescriptive compliance, heating system size, glazing schedule)), and impact fees are included in the bid or billed separately.
How long does it take to build an ADU in Bothell?
Plan for the permit review (Not published: the city's ADU checklist (form 3f, Dec 2025) gives no review time; ask Development Services at 425-806-6400. Add up to two weeks for the water and sewer availability certificate where the City is the provider, and get the address assignment first in Bothell) plus construction. Most detached ADUs take 4-8 months of construction after permits are issued; garage conversions and prefab units are often faster. Ask each builder for a realistic schedule and what could delay it.
Get Free ADU Builder Quotes in Bothell
Compare bids from experienced local Bothell ADU builders. Free, no obligation.
Get Free Quotes →