Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Spokane ADU cost →Building an ADU in Spokane costs between $130,000-$260,000 for new construction, with per-square-foot costs averaging $200-$400. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $50,000-$120,000, while prefab/modular ADUs fall in between at $135,000-$280,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | About $2,000-$3,200 in city fees for a $150,000-$300,000 ADU (2025 New SFR/ADU fee table: $65 processing, plan review at 50% of the permit fee, $100 stormwater review, 2.5% technology fee, $6.50 state fee). A CPI-adjusted 2026 schedule now applies; confirm with the DSC. |
| Impact Fees | Transportation impact fees apply to new dwelling units by service area (SMC 17D.075; schedule in 17D.075.180, Ordinance C36514, indexed up to 5% a year). State law caps an ADU's fee at 50% of the single-family fee (RCW 36.70A.681(1)(a)). The current dollar figure was not readable; ask the DSC for your service area's rate. |
| Site Prep & Foundation | $10,000 – $35,000 |
| Framing & Structure | $15,000 – $45,000 |
| Plumbing | $8,000 – $20,000 |
| Electrical | $5,000 – $15,000 |
| HVAC | $3,000 – $8,000 |
| Interior Finishes | $15,000 – $40,000 |
Quotes for the same ADU commonly vary 20–40% between builders. We pass your request to up to 5 local builders serving Spokane, where we have them — free, no obligation.
Get Spokane builder quotes →Permit fees in Spokane are About $2,000-$3,200 in city fees for a $150,000-$300,000 ADU (2025 New SFR/ADU fee table: $65 processing, plan review at 50% of the permit fee, $100 stormwater review, 2.5% technology fee, $6.50 state fee). A CPI-adjusted 2026 schedule now applies; confirm with the DSC.. The review timeline is The city publishes no ADU-specific review time. State law (RCW 36.70B.080(1)(d)) makes 65 days from a complete application the default for permits that need no public notice, unless Spokane has adopted its own periods; ask the Development Services Center (509-625-6300)., with plan check: Plan review is 50% of the building permit fee for new single-family, ADU and duplex permits and is paid at submittal before the plans are routed (2025 Development Services Fee Schedule); for a $200,000 ADU that is $736 of a $2,416 total.. Impact fees are Transportation impact fees apply to new dwelling units by service area (SMC 17D.075; schedule in 17D.075.180, Ordinance C36514, indexed up to 5% a year). State law caps an ADU's fee at 50% of the single-family fee (RCW 36.70A.681(1)(a)). The current dollar figure was not readable; ask the DSC for your service area's rate.. Pre-approved plans: None found. The city's residential permit pages (August 2026) list an ADU building-permit application but no city pre-approved ADU plan set; the fee schedule offers a stock plan review fee (25% of the job-value fee) for repeat plans, so ask whether a builder's repeat design qualifies..
| 1-Bedroom Rent | $1,050-$1,250/month |
| 2-Bedroom Rent | $1,300-$1,500/month |
| Annual Rental Income (est.) | $13,800/year |
| Payback Period (est.) | 14.1 years |
| Short-Term Rental | Allowed with a short-term rental permit under Chapter 17C.316 SMC, but once a lot with an ADU has a short-term rental, one unit must be owner-occupied for more than six months a year and cannot be rented (SMC 17C.300.110. |
| Overall ROI Estimate | 5-11% gross rent yield: HUD FY2027 fair market rents of $1,173 (1BR) to $1,494 (2BR) a month on a $130,000-$260,000 build, before vacancy, taxes and upkeep |
A typical ADU in Spokane generates approximately $13,800 per year in rental income based on average 1-bedroom rents. At an average construction cost of $195,000, the estimated payback period is 14.1 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Spokane and varies by market (often less than build cost).
1. Garage conversions save 40-60% vs new construction since the shell already exists. Average cost in Spokane: $50,000-$120,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $135,000-$280,000.
3. Pre-approved plans — available in Spokane, which can save $3,000-$10,000 in design costs and 2-3 months in review time. See which cities offer pre-approved ADU plans.
4. State grants — California's CalHFA ADU grant (up to $40K) is currently paused; check calhfa.ca.gov/adu for status and your state for active programs.
5. Get multiple bids — ADU contractor pricing varies 20-40% for the same project. We recommend getting at least 3 quotes.
Tell us about your project and we'll pass it to ADU builders serving Spokane. 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.
🔒 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.