Yes. Bothell allows two accessory dwelling units on every residential lot, each up to 1,200 sq ft, with no owner-occupancy rule and, since Ordinance 2461 took effect in July 2025, no off-street parking requirement at all (BMC 12.14.135; BMC 12.16.030). A detached ADU may be 30 ft tall (33 ft over an existing garage), is exempt from the rule capping accessory buildings at 5 percent of the lot, and keeps the same rear setback as the house: 35 ft in R-C, 15 ft in R-L1 and R-L2, 10 ft in the R-M zones, 0 ft on an alley (BMC 12.14.070(B), 12.14.030(A)). Bothell's own code grants one ADU even on a critical-area lot, which state law leaves unprotected (BMC 12.14.135(C)). It is an ordinary building permit filed through MyBuildingPermit.com: a $300,000 detached ADU runs about $7,700 in city permit fees, plus impact fees of roughly $4,400-$5,650 (transportation $3,311 from May 1, 2026, fire $232, park at half the house's rate) before any school fee, all capped at 50 percent of what a house pays.
In Bothell you will also hear an ADU called a DADU — short for detached accessory dwelling unit, the usual term across Washington. The rules on this page apply either way.
Outside city limits? If your property is in unincorporated King County (not within Bothell's boundaries), different rules apply — see our King County (unincorporated) ADU rules.
Zoning & Size Requirements [1][2][3][4][5][6][7][8][9]
Yes — Bothell allows ADUs. A detached ADU can typically be up to 1,200 sq ft under current Washington and Bothell zoning rules.
See what this means for your lot — ask Bothell ADU builders for a quote →
| Allowed Zones | All residential zones: R-C, R-L1, R-L2 and R-M1 through R-M4. The Residential Development Standards table carries a "Maximum ADUs per lot" row of 2 and BMC 12.14.135 permits ADUs with no zone limit (BMC 12.14.030(A), 12.14.135). The use table at BMC 12.06.140 listed ADUs as permitted in every residential zone when last read Sept 1, 2026. RCW 36.70A.681(1)(c) requires two ADUs wherever single-family homes are allowed inside the urban growth area. Confirm your zone: 425-806-6400 |
| Max Size (Detached) | 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 |
| Max Size (Attached) | Same 1,200 sq ft cap (BMC 12.14.135(D)(1)). An ADU created by converting existing space may exceed 1,200 sq ft as approved by the community development director, provided it does not exceed 40 percent of the primary dwelling unit's gross floor area. An attached ADU is part of the house for height and setbacks and takes the zone's principal-building standards |
| Max Size (JADU) | Washington has no junior ADU category and Bothell's code has none. An ADU built inside the existing house is an ordinary attached ADU under BMC 12.14.135 and may use the conversion allowance in 12.14.135(D)(1), so it can exceed 1,200 sq ft within 40 percent of the house's gross floor area |
| Max Height | 30 ft for a detached ADU, or 33 ft for a unit built over an existing accessory structure (BMC 12.14.135(E)). The principal-building limit is 35 ft in R-C, R-L1, R-L2, R-M1 and R-M2, 45 ft in R-M3 and 55 ft in R-M4 (BMC 12.14.030(A)); an attached ADU is part of the house and takes that limit. Both sit above the 24-ft floor in RCW 36.70A.681(1)(g) |
| Max Units | Two per lot: "Two accessory dwelling units are allowed per lot" (BMC 12.14.135(A)); the standards table's "Maximum ADUs per lot" row reads 2 for R-C, R-L1, R-L2 and R-M1 (BMC 12.14.030(A)). One ADU where the lot holds middle housing (BMC 12.14.135(B)) and one on lots designated with critical areas or their buffers (BMC 12.14.135(C)), a local grant, since RCW 36.70A.681(4) exempts critical-area lots from every state ADU protection |
Setback Requirements [1][2][3][4][5][6][7][8][9]
Bothell requires a rear setback of about 35 ft for a detached ADU, and parking requirements vary by unit size or location. Owner-occupancy is not required — you can rent it out without living on the property.
| Rear Setback | Same as the house. "Detached accessory dwelling units shall maintain the same rear yard setback as primary structures, except for those accessory dwelling units located on an alley, in which case the setbacks for structures adjoining alleys in BMC 12.14.060 shall apply" (BMC 12.14.070(B), quoted on the city's ADU checklist). Zone minimums: 35 ft in R-C, 15 ft in R-L1 and R-L2, 10 ft in R-M1 through R-M4; on an alley 0 ft, 3 ft for a garage door (BMC 12.14.030(A)) |
| Side Setback | 5 ft in every residential zone (BMC 12.14.030(A), Residential Development Standards table as amended by Ord. 2461, July 2025); a detached ADU takes the principal-structure standard. Measurement rules are at BMC 12.14.050 through 12.14.100 and permitted projections into a setback at BMC 12.14.090. State law bars ADU setbacks stricter than the house's (RCW 36.70A.681(1)(h)) |
| Front Setback | 15 ft in R-C, R-L1 and R-L2 and 10 ft in R-M1 through R-M4; any garage door must be 20 ft back (BMC 12.14.030(A)). The front setback may hold no hard surface other than a driveway no wider than three cars, a walkway up to 5 ft wide and projections allowed by BMC 12.14.090 (BMC 12.14.030(B)(6)) |
| Parking Required | None. Ordinance 2461 (adopted July 8, 2025) struck the ADU parking subsection from BMC 12.14.135 and deleted the minimum-parking table in BMC 12.16.030, including "Dwelling units, accessory: 1 per unit"; the section now reads "Except as provided herein, there is no required minimum number of off-street parking spaces." The old transit and trail waivers in 12.16.110(F) went with it. You may still build a space; the site plan must show any you keep or add. State floor: RCW 36.70A.681(2)(a) |
| 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)) |
| Min Lot Size | No ADU-specific minimum; state law requires an ADU on any lot that meets the principal unit's minimum (RCW 36.70A.681(1)(e)). Lot minimums are 40,000 sq ft in R-C, 6,000 in R-L1, 3,600 in R-L2 and none in R-M1 through R-M4 (BMC 12.14.030(A)). The binding limit for a detached ADU is hard surface coverage: 35 percent of the lot in R-C, 55 in R-L1, 60 in R-L2, 70 in R-M1, 75 in R-M2, since Ord. 2461 dropped the building-coverage row and 12.14.135(D)(2) waives the 5 percent accessory-building cap |
Permit Process & Fees [10][11][12][13][14][15][16]
An ADU permit in Bothell goes through a standard permit review. 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. Permit 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.
| Approval 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 |
| Review Timeline | 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 |
| Permit 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 |
| 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 |
| 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) |
| Pre-Approved Plans | None. The city has no pre-approved ADU plan program: the ADU checklist assumes a custom plan set, and the draft Housing Action Plan presented to Council on June 9, 2026 (adoption by resolution expected December 2026) only lists "pre-designed layout plans for ADUs" as an idea to explore. Confirm with Development Services at 425-806-6400 |
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Construction Costs [17][18][19][20]
Building an ADU in Bothell typically costs $325,000-$550,000 ($400-$650 per sq ft); a garage conversion runs $100,000-$225,000.
See what this means for your lot — ask Bothell ADU builders for a quote →
| Average Build Cost | $325,000-$550,000 |
| Cost per Sq Ft | $400-$650 |
| Garage Conversion | $100,000-$225,000 |
| Prefab ADU (Installed) | $300,000-$450,000 |
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Rental Income Potential [21]
A 2-bedroom ADU in Bothell rents for around $2,700-$3,150/mo, an estimated 5-8% annual return.
| Avg Rent (1 Bedroom) | $2,300-$2,700/mo |
| Avg Rent (2 Bedroom) | $2,700-$3,150/mo |
| Short-Term Rental | Not regulated by an ADU-specific rule. |
| Est. Annual ROI | 5-8% annual return |
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Recent Law Changes
What's Changed Recently
- Ordinance 2461 (Phase 2 Comprehensive Plan code updates, adopted July 8, 2025 by a 5-1-1 vote; effective five days after publication) eliminated minimum off-street parking citywide: it struck the one-stall ADU parking subsection from BMC 12.14.135, deleted the minimum-parking table in BMC 12.16.030 (including the "Dwelling units, accessory" row) and the ADU transit and trail waivers in 12.16.110(F), and removed the separate maximum building coverage row from the residential standards table so hard surface coverage is now the only coverage limit
- Transportation impact fee update (BMC 17.045.070, adopted March 10, 2026 by a 6-0-1 vote, effective May 1, 2026): the ADU rate is $3,311 per unit (0.33 net new person trips at $9,928 per trip) against $13,387 for a single-family house, up from $1,742 under the 2020 schedule, plus a 3 percent administrative fee. A 10 percent reduction applies to residential uses other than detached single-family within a quarter mile of rapid transit and inside the Canyon Park, Midtown and Downtown growth centers
- The city's 2026 impact fee form (form X, updated April 2026) sets the ADU fire impact fee at $232.30 ($229.34 sprinklered), the ADU park impact fee at 50 percent of the principal unit's, and school impact fees of $16,550 per single-family and $5,945 per multifamily unit from January 1, 2026, with no ADU row for the school fee
- Washington HB 1337 (2023 c 334), codified at RCW 36.70A.681, sets the floor Bothell must meet: two ADUs on every lot in a zone that allows single-family homes inside the urban growth area, no owner-occupancy requirement, no size cap under 1,000 sq ft, no height limit under 24 ft, no setbacks stricter than the house's, conversions of existing structures allowed, detached ADUs at an alley lot line, impact fees capped at half the principal unit's, no street improvements, no parking within half a mile walking distance of a major transit stop, and no bar on selling a condominiumized ADU separately
- Bothell's Housing Action Plan: the draft was presented to Council on June 9, 2026 and adoption by resolution is expected in December 2026. Its ADU objective is to explore grants or low-interest loans tied to deed-restricted affordability and pre-designed ADU layout plans; nothing has been adopted and no fee waiver or plan gallery exists yet
- Text status: BMC 12.14.135 was verified from the codified section current through Ordinance 2464 (September 16, 2025; Internet Archive capture of November 18, 2025) and from the adopted ordinance exhibits; the live code host blocks automated access. No Council action on ADU standards was found in agendas from May through September 2026
Tips for Building an ADU in Bothell
- You can build two, and on a critical-area lot you can still build one. BMC 12.14.135(C) is the line to quote if a reviewer or contractor says a wetland or steep-slope designation kills the project: state law would, Bothell's code does not
- Do not let a designer draw a parking stall out of habit. Since Ordinance 2461 (July 2025) Bothell requires no off-street parking for an ADU anywhere in the city; if you want one, a driveway or carport counts, and the site plan simply has to show whatever spaces you keep or add
- Hard surface coverage is the real size limit. On a 6,000 sq ft R-L1 lot the 55 percent cap allows 3,300 sq ft of roof, driveway, walkway and patio combined, house included; count everything before you size a detached unit (BMC 12.14.030(A), 12.14.140)
- Converting existing space beats building new on size: a conversion may exceed 1,200 sq ft with the community development director's approval, up to 40 percent of the house's gross floor area (BMC 12.14.135(D)(1))
- If your lot adjoins an alley, the rear setback drops from 15 ft (R-L1, R-L2) or 35 ft (R-C) to zero, 3 ft for a garage door (BMC 12.14.030(A), 12.14.070(B)). On a shallow lot that is the difference between a buildable backyard and none
- Worked impact fees for an 800 sq ft detached ADU behind a 1,500 sq ft house: transportation $3,311 plus $99 administration, fire $232.30, park half of the house's $3,285.20 bracket ($1,642.60), about $5,285 before the school fee. Ask Development Services which school rate applies to an ADU and hold them to the 50 percent cap ($8,275 at most against the $16,550 single-family rate)
- Which county you are in changes the agencies, not the city fees: septic sign-off comes from King County Public Health (98011) or the Snohomish Health District (98012, 98021), and the water and sewer availability certificate from your provider (City of Bothell, Alderwood, Northshore or Woodinville). The city's 2026 permit and impact fee forms apply on both sides
- Get the address assigned first (form 54); the city will not accept the ADU application without it, and a City of Bothell water and sewer availability certificate takes up to two weeks on its own
- Already have an unpermitted unit? BMC 12.14.135(F) gives you a route: apply, take the building inspection, which the ADU application fee covers, and get it legal rather than waiting for a complaint
- Cost basis: the ranges are Seattle-metro 2025-2026 industry guides (site-built detached $325,000-$550,000 at $400-$650 per sq ft; conversions $100,000-$225,000; prefab installed $300,000-$450,000). Bothell fees on top: about $7,700 in permit fees and $4,400-$5,650 in impact fees before any school fee, plus water, sewer and stormwater facility charges from your provider
- Cost basis (2026-09-20 re-verification): short term allowed: Not regulated by an ADU-specific rule. BMC 12.14.135 sets no minimum tenancy, and no short-term rental chapter or city web page could be found on bothellwa.gov as of Sept 20, 2026; the codified code host could not be read, so confirm with the City of Bothell at 425-806-6400 before listing, and expect a state business licence with a Bothell city endorsement for any rental business. Long-term rental of an ADU is unrestricted: there is no owner-occupancy rule and no cap on renting the unit
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Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- Bothell Municipal Code 12.14.135 — Accessory dwelling units (Ord. 2461 § 1 (Exh. A), 2025; Ord. 2445, 2024; Ord. 2415, 2024), codified text current through Ord. 2464 (Sept 16, 2025), Internet Archive capture of Nov 18, 2025 Municipal Code — Accessed 2026-09-20
- Bothell Municipal Code 12.14.135 — Accessory dwelling units (live code host; blocks automated access) Municipal Code — Accessed 2026-09-01
- Ordinance 2461 (2025) — Parking ordinance, Phase 2 Comprehensive Plan Code Updates: Exhibit A (BMC 12.14.030 table, 12.14.134, 12.14.135) and Exhibit B (BMC 12.16.030, 12.16.110), City Council agenda packet July 8, 2025, AB 25-125 Att-5 Municipal Code — Accessed 2026-09-20
- City Council minutes, July 8, 2025 — Phase 2 Comprehensive Plan Code Updates ordinances adopted 5-1-1 Planning Department — Accessed 2026-09-20
- Bothell Municipal Code 12.14.030 — Residential area and dimensions (Residential Development Standards table, as amended by Ord. 2461, 2025) Municipal Code — Accessed 2026-09-20
- Bothell Municipal Code 12.06.140 — Residential uses (use table and development conditions) Municipal Code — Accessed 2026-09-01
- Bothell Municipal Code 12.14.070(B) — Setbacks applying to specific buildings or uses (rear setback for detached ADUs, as quoted on the city's ADU checklist) Municipal Code — Accessed 2026-09-20
- Bothell Municipal Code 12.16.030 — No minimum required off-street parking spaces (Ord. 2461, 2025) Municipal Code — Accessed 2026-09-20
- RCW 36.70A.681 — Accessory dwelling units, limitations on local regulation (2023 c 334 s 4, HB 1337) state_statute — Accessed 2026-09-20
- Accessory Dwelling Unit submittal checklist (form 3f), City of Bothell Development Services, updated December 2025 — 2026 fees Planning Department — Accessed 2026-09-20
- Building Permit Fees 2026 (form A), City of Bothell Development Services, updated December 2025 — Table 20.02.155-A, plan check, energy, state and technology fees Planning Department — Accessed 2026-09-20
- 2026 Impact Fees (form X), City of Bothell Development Services, updated April 2026 — fire (BMC 21.16), school (BMC 21.12), park (BMC 21.08) and transportation (BMC 17.045) rates Planning Department — Accessed 2026-09-20
- Bothell Municipal Code Title 17 amendments including Transportation Impact Fees (AB 26-035; ordinance with BMC 17.045.070 schedule, effective May 1, 2026), City Council agenda packet March 10, 2026 Municipal Code — Accessed 2026-09-20
- City Council minutes, March 10, 2026 — Title 17 transportation impact fee ordinance adopted 6-0-1 Planning Department — Accessed 2026-09-20
- Draft Housing Action Plan staff briefing, City Council agenda June 9, 2026 (adoption by resolution expected December 2026) Planning Department — Accessed 2026-09-20
- Council Adopts City Code Changes for Parking and Small Business Permitting — City of Bothell news, July 9, 2025 Planning Department — Accessed 2026-09-20
- Cost to Build a DADU in Seattle (2025-2026 Update) | Ballard Backyard Cottages industry — Accessed 2026-09-19
- How Much Does It Cost to Build an ADU in Seattle? 2026 Guide (Jan. 8, 2026) | Kolmo industry — Accessed 2026-09-19
- Seattle ADU Cost 2026 by Type and Size (updated May 12, 2026) | ADU Glossary industry — Accessed 2026-09-19
- Prefab ADU 2026: Brands, True Costs (updated May 19, 2026) | OwnADU industry — Accessed 2026-09-19
- HUD FY 2026 and FY 2027 Small Area Fair Market Rents, Seattle-Bellevue, WA HUD Metro FMR Area, ZIP codes 98011, 98012 and 98021 Government Data — Accessed 2026-09-20
- Washington State Office of Financial Management — April 1, 2026 Population of Cities, Towns and Counties Government Data — Accessed 2026-09-01
Frequently Asked Questions
Can I build an ADU in Bothell?
Yes. ADUs are allowed in All residential zones: R-C, R-L1, R-L2 and R-M1 through R-M4. The Residential Development Standards table carries a "Maximum ADUs per lot" row of 2 and BMC 12.14.135 permits ADUs with no zone limit (BMC 12.14.030(A), 12.14.135). The use table at BMC 12.06.140 listed ADUs as permitted in every residential zone when last read Sept 1, 2026. RCW 36.70A.681(1)(c) requires two ADUs wherever single-family homes are allowed inside the urban growth area. Confirm your zone: 425-806-6400 in Bothell. The maximum size for a detached ADU is 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 is not required, so you can rent out the ADU.
How much does an ADU cost in Bothell?
ADU construction in Bothell typically costs $325,000-$550,000. Garage conversions run $100,000-$225,000, and prefab ADUs cost $300,000-$450,000.
How much can I rent an ADU for in Bothell?
Average ADU rents in Bothell are $2,300-$2,700/mo for a 1-bedroom and $2,700-$3,150/mo for a 2-bedroom unit.
Do I need parking for an ADU in Bothell?
None. Ordinance 2461 (adopted July 8, 2025) struck the ADU parking subsection from BMC 12.14.135 and deleted the minimum-parking table in BMC 12.16.030, including "Dwelling units, accessory: 1 per unit"; the section now reads "Except as provided herein, there is no required minimum number of off-street parking spaces." The old transit and trail waivers in 12.16.110(F) went with it. You may still build a space; the site plan must show any you keep or add. State floor: RCW 36.70A.681(2)(a). Check with Bothell planning department for the latest Washington ADU parking rules, as many states have relaxed requirements in recent years.
How long does it take to get an ADU permit in Bothell?
Bothell does not publish a standard ADU review timeline. 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. Permit 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.
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