An ADU builder in Sammamish 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 Sammamish'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 Sammamish [17][18][19][20]
Based on our Sammamish 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 | Value-based (2026 Development Fee Schedule): $1,278.51 on the first $100,000 plus $8.65 per $1,000 above it, plus plan review at 65 percent, a $1,578 planning review, $544 plan-review support ($2,248 on a critical-area site) and a 15 percent technology fee — about $11,150 on a $400,000 ADU. |
| Impact Fees | Per square foot since July 1, 2026 (Ord. O2026-595, new SMC 21.06.045, adopted to meet SB 5258's amendment of RCW 82.02.060(1)): parks $3.13 and transportation $7.44 per sq ft, each with a 783 sq ft minimum ($2,450.79 and $5,825.06 — $8,275.85 together) and a 3,500 sq ft maximum ($10,955 and $26,040). A 1,000 sq ft ADU pays $10,570. School fees are per dwelling unit by district — Lake Washington SD $10,914.75, Issaquah SD $0.00, Snoqualmie Valley SD $19,690.27 at the single-family rate, plus a $266 administration fee; the schedule lists no ADU category, and RCW 36.70A.681(1)(a) caps any ADU impact fee at 50 percent of the principal unit's (at most $5,457.38 in Lake Washington SD), except on critical-area lots (subsection (4)). Fees are due at permit issuance but may be deferred to occupancy for up to 18 months against a recorded lien (SMC 21.06.045(I)); parks and transportation rates are indexed to the ENR Construction Cost Index each first quarter. |
For a full line-item breakdown, see our Sammamish ADU cost guide. To confirm what you're allowed to build before you hire, review the Sammamish ADU rules (max detached size: 1,000 sq ft of floor area: "The ADU must not exceed a floor area of 1,000 square feet" (SMC 21.05.010.C(5)(a)(iii)) — the floor RCW 36.70A.681(1)(f) sets, not a foot more. ADUs are listed as "Exempt" from the 50 percent residential floor area ratio in R-1 through R-8, and SMC 21.04.030.C condition (10) exempts them from hardscape coverage (30 percent in R-1, 40 percent in R-4) and FAR calculations on a single-family lot. The 3,000 sq ft maximum building footprint per building still applies.; owner-occupancy: Not required. SMC 21.05.010.C(5)(a) as rewritten by Ord. O2024-578 (effective January 1, 2025) has no owner-occupancy condition, recorded notice or conversion-or-removal clause; the pre-2025 code required one unit to be owner-occupied and a notice recorded with King County. RCW 36.70A.681(1)(b) bars reinstating it: a city "may not require the owner of a lot on which there is an accessory dwelling unit to reside in or occupy the accessory dwelling unit or another housing unit on the same lot.").
Get Free ADU Quotes in Sammamish
Tell us about your project and we'll pass it to ADU builders serving Sammamish. 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 Sammamish
- 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 Sammamish 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 (Value-based (2026 Development Fee Schedule): $1,278.51 on the first $100,000 plus $8.65 per $1,000 above it, plus plan review at 65 percent, a $1,578 planning review, $544 plan-review support ($2,248 on a critical-area site) and a 15 percent technology fee — about $11,150 on a $400,000 ADU.), plan check (Standard building plan review through MyBuildingPermit.com, plus critical-areas review on many Sammamish sites: the Building Plan Review Support fee is $2,248 for a "Single family house/ADU - Critical Area" against $544 otherwise, a third-party critical area report review takes a $5,000 deposit, and wetland, stream, landslide, erosion, habitat and aquifer-recharge worksheets are on the city's forms page. A minor clearing-and-grading permit (up to 100 cubic yards) is billed at $267 planning plus $543 public-works review. Tree removal is separately permitted ($139), and unlawful removal is charged at $1,500 per inch of diameter at breast height. Concurrency testing for a "Single family house/ADU" is $280 plus $144 processing and a $187 administrative fee.), and impact fees (Per square foot since July 1, 2026 (Ord. O2026-595, new SMC 21.06.045, adopted to meet SB 5258's amendment of RCW 82.02.060(1)): parks $3.13 and transportation $7.44 per sq ft, each with a 783 sq ft minimum ($2,450.79 and $5,825.06 — $8,275.85 together) and a 3,500 sq ft maximum ($10,955 and $26,040). A 1,000 sq ft ADU pays $10,570. School fees are per dwelling unit by district — Lake Washington SD $10,914.75, Issaquah SD $0.00, Snoqualmie Valley SD $19,690.27 at the single-family rate, plus a $266 administration fee; the schedule lists no ADU category, and RCW 36.70A.681(1)(a) caps any ADU impact fee at 50 percent of the principal unit's (at most $5,457.38 in Lake Washington SD), except on critical-area lots (subsection (4)). Fees are due at permit issuance but may be deferred to occupancy for up to 18 months against a recorded lien (SMC 21.06.045(I)); parks and transportation rates are indexed to the ENR Construction Cost Index each first quarter.) are included.
- Permit handling: Confirm they manage Sammamish's permit process ("A building permit only — no conditional use permit, no hearing and, since Ord. O2024-578, no recorded notice; SMC 21.05.010.C development condition (9) exempts ADUs from the approval otherwise required for more than one dwelling on a lot. All applications are submitted online at MyBuildingPermit.com; the Permit Center (425-295-0531, PermitTech@sammamish.us; walk-ins Monday and Friday 9am-noon, Wednesday 1-4pm, virtual appointments with plans examiners, planners and review engineers) answers questions but issues no permits at a visit. Start with the free Project Guidance request, answered within one week, which reports setbacks, critical-area designations and next steps for your parcel — the step that decides most plateau projects, because RCW 36.70A.681(4) removes the state protections on a lot designated with critical areas or their buffers. The city may not require public street improvements as a condition of an ADU permit (RCW 36.70A.681(1)(l)). In September 2026 the city warns of reduced service levels during a staff transition.", typically Not published — the city sets no ADU-specific review clock, and in September 2026 warns of reduced service levels during a staff transition. Project Guidance is answered within one week; ask the Permit Center (425-295-0531) for the current building-permit review target before you submit.) 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 Sammamish 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 sets no ADU-specific review clock, and in September 2026 warns of reduced service levels during a staff transition. Project Guidance is answered within one week; ask the Permit Center (425-295-0531) for the current building-permit review target before you submit.) 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 Sammamish leads
Homeowners on this page submit real ADU project requests in Sammamish. 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 Sammamish ADU Leads →Frequently Asked Questions
How much do ADU builders charge in Sammamish?
ADU builders in Sammamish 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 (Value-based (2026 Development Fee Schedule): $1,278.51 on the first $100,000 plus $8.65 per $1,000 above it, plus plan review at 65 percent, a $1,578 planning review, $544 plan-review support ($2,248 on a critical-area site) and a 15 percent technology fee — about $11,150 on a $400,000 ADU.) plus impact fees of Per square foot since July 1, 2026 (Ord. O2026-595, new SMC 21.06.045, adopted to meet SB 5258's amendment of RCW 82.02.060(1)): parks $3.13 and transportation $7.44 per sq ft, each with a 783 sq ft minimum ($2,450.79 and $5,825.06 — $8,275.85 together) and a 3,500 sq ft maximum ($10,955 and $26,040). A 1,000 sq ft ADU pays $10,570. School fees are per dwelling unit by district — Lake Washington SD $10,914.75, Issaquah SD $0.00, Snoqualmie Valley SD $19,690.27 at the single-family rate, plus a $266 administration fee; the schedule lists no ADU category, and RCW 36.70A.681(1)(a) caps any ADU impact fee at 50 percent of the principal unit's (at most $5,457.38 in Lake Washington SD), except on critical-area lots (subsection (4)). Fees are due at permit issuance but may be deferred to occupancy for up to 18 months against a recorded lien (SMC 21.06.045(I)); parks and transportation rates are indexed to the ENR Construction Cost Index each first quarter.. 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 Sammamish?
Look for a licensed contractor with completed ADU projects in Sammamish 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 Sammamish for free quotes.
Do ADU builders in Sammamish handle permits?
Most full-service ADU builders manage the permit process for you. In Sammamish the approval process is "A building permit only — no conditional use permit, no hearing and, since Ord. O2024-578, no recorded notice; SMC 21.05.010.C development condition (9) exempts ADUs from the approval otherwise required for more than one dwelling on a lot. All applications are submitted online at MyBuildingPermit.com; the Permit Center (425-295-0531, PermitTech@sammamish.us; walk-ins Monday and Friday 9am-noon, Wednesday 1-4pm, virtual appointments with plans examiners, planners and review engineers) answers questions but issues no permits at a visit. Start with the free Project Guidance request, answered within one week, which reports setbacks, critical-area designations and next steps for your parcel — the step that decides most plateau projects, because RCW 36.70A.681(4) removes the state protections on a lot designated with critical areas or their buffers. The city may not require public street improvements as a condition of an ADU permit (RCW 36.70A.681(1)(l)). In September 2026 the city warns of reduced service levels during a staff transition.". Review time: not published — the city sets no ADU-specific review clock, and in September 2026 warns of reduced service levels during a staff transition. Project Guidance is answered within one week; ask the Permit Center (425-295-0531) for the current building-permit review target before you submit. Confirm in writing whether permit fees, plan check (Standard building plan review through MyBuildingPermit.com, plus critical-areas review on many Sammamish sites: the Building Plan Review Support fee is $2,248 for a "Single family house/ADU - Critical Area" against $544 otherwise, a third-party critical area report review takes a $5,000 deposit, and wetland, stream, landslide, erosion, habitat and aquifer-recharge worksheets are on the city's forms page. A minor clearing-and-grading permit (up to 100 cubic yards) is billed at $267 planning plus $543 public-works review. Tree removal is separately permitted ($139), and unlawful removal is charged at $1,500 per inch of diameter at breast height. Concurrency testing for a "Single family house/ADU" is $280 plus $144 processing and a $187 administrative fee.), and impact fees are included in the bid or billed separately.
How long does it take to build an ADU in Sammamish?
Plan for the permit review (Not published — the city sets no ADU-specific review clock, and in September 2026 warns of reduced service levels during a staff transition. Project Guidance is answered within one week; ask the Permit Center (425-295-0531) for the current building-permit review target before you submit. in Sammamish) 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 Sammamish
Compare bids from experienced local Sammamish ADU builders. Free, no obligation.
Get Free Quotes →