Best ADU Builders Spokane (2026): How to Choose a Contractor Who Knows the Permit Process
Bottom line up front.
If you are searching for the best ADU builders in Spokane in 2026, the most important qualifying criterion is this: does the builder know Spokane's specific ADU permit code — SMC 17C.300.110 — and can they prepare a complete permit packet that passes counter review on the first submission? The City of Spokane's Development Services Center rejects incomplete permit applications at the counter, which resets the clock entirely. Builders who do not know the Spokane-specific submittal requirements — energy worksheet, complete site plan, stamped structural drawings, correct application forms — will cost you time before a single permit fee is paid.
No builder can guarantee permit approval or timelines. Regulations and fees can change. Verify all information with Spokane's Development Services Center before signing a contract.
Source: The Dwelling Index independent research; City of Spokane Development Services; Washington State Department of Commerce ADU resources. Last verified: June 12, 2026.
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What SMC 17C.300.110 requires: the Spokane ADU code in plain language
Spokane Municipal Code Section 17C.300.110 is the primary ADU regulation governing single-family residential properties within the City of Spokane. Key provisions:
| Requirement | Current standard (verify with DSC) |
|---|---|
| Detached ADU max size | 1,000 square feet |
| Attached ADU max size | 50% of primary dwelling gross floor area or 1,000 sq ft, whichever is less |
| Maximum height | Typically 25 feet or matches the primary structure allowance; varies by zone |
| Setbacks | Rear and side setbacks apply; verify current minimums for your zone with DSC |
| Lot coverage | ADU counts toward total lot coverage; verify your lot's maximum |
| Entrance | ADU must have a separate exterior entrance |
| Number allowed | One ADU per single-family lot |
Always verify current code requirements with the City of Spokane Development Services Center. Ordinances are updated periodically.
Three Spokane-area jurisdictions: City, Valley, and County
The greater Spokane area includes three distinct permit jurisdictions. Before engaging any builder, confirm which jurisdiction your parcel falls under:
- City of Spokane. Governed by Spokane Municipal Code (SMC). Permit applications are submitted to the Development Services Center at City Hall. ADU rules under SMC 17C.300.110.
- City of Spokane Valley. A separate incorporated city with its own municipal code, planning department, and permit office. Not part of the City of Spokane permit system. ADU rules and fees differ.
- Unincorporated Spokane County. Governed by Spokane County Code and the County Division of Building and Planning. Different from both city jurisdictions. ADU standards may differ from city rules.
A builder experienced only in the City of Spokane may have zero familiarity with Spokane Valley or County permit processes. Ask specifically which jurisdiction your parcel falls under and confirm the builder has completed ADU permits in that exact jurisdiction.
What a complete Spokane ADU permit packet requires
The City of Spokane's Development Services Center reviews permit packets at the counter before accepting them for formal review. An incomplete packet is rejected immediately, resetting the process. A complete ADU permit packet in the City of Spokane typically requires:
- Site plan. Showing the existing primary dwelling, proposed ADU footprint, property lines, setbacks, utility connections (water, sewer, electrical), driveway, and any easements.
- Architectural drawings. Floor plans, exterior elevations (all four sides), building cross-section, and roof plan. Must meet minimum drawing standards.
- Structural drawings. Foundation plan, framing plan, and details. Must be stamped by a Washington-licensed structural engineer if not using prescriptive framing.
- Energy code compliance worksheet. Washington State Energy Code compliance documentation — a completed energy worksheet, REScheck, or equivalent. This is a common reason for counter rejection.
- Application forms. Completed City of Spokane building permit application with correct valuation, contractor information, and owner signatures.
- Geotechnical report. Required for sites with steep slopes, fill soils, expansive soils, or proximity to watercourses. Not required for flat, stable sites.
Ask any Spokane ADU builder to walk you through each required submittal element and confirm they have submitted complete packets that passed counter review on the first attempt in the City of Spokane.
Budget in hand — now find the right financing path.
Most Spokane ADU projects are financed with a HELOC, cash-out refinance, or construction loan. Each has different rate behavior, draw timing, and tax treatment.
Compare ADU Financing Paths →Financing-path education; we don't quote rates as guarantees.
Washington state ADU law: RCW 36.70A.681 and what it means for Spokane
Washington state law under RCW 36.70A.681 mandates that cities and counties planning under the Growth Management Act (GMA) — which includes Spokane — must allow ADUs by right in all single-family residential zones. Key protections:
- ADUs must be allowed. Cities cannot prohibit ADUs outright or impose restrictions that functionally prevent ADU construction.
- Ministerial approval. ADUs meeting objective standards must be approved administratively, without discretionary review or public hearings.
- Owner-occupancy prohibition. Washington state law removed mandatory owner-occupancy requirements for ADUs in GMA jurisdictions. Local ordinances imposing owner-occupancy conditions may not be enforceable under state law.
- Size limits. State law establishes minimum allowable ADU sizes. Local size caps that are more restrictive than state minimums may not be enforceable.
If a Spokane builder or city planner cites a local restriction that appears to conflict with state law, ask for the specific ordinance section and verify against Washington Department of Commerce guidance.
Seven questions to ask every Spokane ADU builder
- Have you pulled ADU permits specifically in the City of Spokane (or my jurisdiction)? Ask for permit numbers or completed project addresses you can verify with the Development Services Center.
- Can you walk me through the SMC 17C.300.110 requirements for my lot? A builder who cannot name the relevant code section, the setback requirements for your zone, and the maximum size for your ADU type is not prepared for Spokane.
- What do you include in your permit packet submittal? A complete answer includes site plan, architectural drawings, structural drawings, energy code worksheet, application forms, and any site-specific reports required.
- Have you had a permit packet rejected at the counter? Every experienced builder has encountered this. Ask how they handle rejections and what their first-pass acceptance rate is.
- What utility work is included in your quote? Water and sewer connections, panel upgrades, and trenching are common cost variables. Get them in writing.
- What is your Washington contractor registration number? All contractors performing work in Washington must be registered with the Department of Labor and Industries (L&I). Verify at lni.wa.gov.
- Can you provide verified references for completed Spokane ADUs? Ask specifically for City of Spokane permit numbers and completed project addresses you can look up.
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Download the Free ADU Starter Kit →Frequently asked questions
What is the maximum ADU size in the City of Spokane?
For detached ADUs on a single-family lot in the City of Spokane, the maximum size is 1,000 square feet under SMC 17C.300.110. Attached ADUs may be governed by different size limits depending on the primary dwelling. Verify current size limits with Spokane's Development Services Center before committing to a unit size.
Does the City of Spokane require energy worksheets for new ADUs?
Yes. The City of Spokane requires Washington State Energy Code compliance documentation for new ADU construction. Builders should be prepared to submit a completed energy worksheet or COMcheck/REScheck as part of a complete permit packet. An incomplete energy compliance submittal is a common cause of permit rejection at the counter.
What three jurisdictions should Spokane ADU homeowners know about?
The Spokane metro area contains three distinct permit jurisdictions: the City of Spokane (governed by SMC), the City of Spokane Valley (its own municipal code), and unincorporated Spokane County (governed by county code). Each has separate permit offices, separate fee schedules, and may have different ADU standards. Confirm which jurisdiction your parcel falls under before engaging a builder.
Does Washington state law override restrictive local ADU rules in Spokane?
Yes. Under RCW 36.70A.681 and amendments through 2023, Washington state mandates that all cities and counties planning under the Growth Management Act must allow ADUs by right on all lots with single-family zoning. Local restrictions that prohibited ADUs or imposed excessive barriers were required to be brought into compliance. If a Spokane builder or planner cites a local restriction that appears to conflict with state law, ask for the specific code section and verify against current Department of Commerce guidance.
What should a complete Spokane ADU permit packet include?
A complete City of Spokane ADU permit packet typically requires: a site plan showing the existing primary dwelling, proposed ADU, setbacks, and utility connections; architectural drawings with floor plans, elevations, and sections; a foundation plan stamped by a licensed engineer if the design is not prescriptive; an energy compliance worksheet; a soils report if the site has challenging soil or slope conditions; and applicable application forms. An incomplete submittal — missing any of these — will be rejected at the counter, delaying the clock.
Is owner-occupancy required for Spokane ADUs?
Washington state law removed mandatory owner-occupancy requirements for ADUs in cities and counties planning under the GMA. Verify the current status of any owner-occupancy conditions in the City of Spokane Municipal Code with Spokane's Development Services Center, as local ordinances are updated on a rolling basis and may have conditions tied to specific permit types or zones.
Editorial independence: The Dwelling Index does not accept payment for builder placement. No builder mentioned in this guide has paid for inclusion, ranking, or editorial coverage. All guidance is based on independent research. Regulations change; verify all information with the City of Spokane Development Services Center before signing a contract.