Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Redmond ADU cost →Building an ADU in Redmond costs between $325,000-$550,000 for new construction, with per-square-foot costs averaging $400-$650. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $100,000-$225,000, while prefab/modular ADUs fall in between at $300,000-$450,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | Valuation-based (Residential Building Permit Fees, effective Feb. 1, 2025): a $300,000 detached ADU is about $4,069 permit + $2,645 plan review (65%) + $795 planning + $767 fire + 4% technology surcharge, roughly $8,600 before impact and utility fees |
| Impact Fees | Capped by state law at 50 percent of what the principal unit would pay (RCW 36.70A.681(1)(a)); RMC 3.10 itself carries no ADU line or exemption. For scale, the adopted single-family rates are $148.78 fire, $6,778.37 park and $5,972.00 school (plus a $65 school admin fee) per unit, and a transportation impact fee of $10,022.14 per Single-Family Detached unit ($7,604.20 in Centers) or $5,757.40 for Middle Housing ($4,368.37 in Centers), the category whose ITE basis includes ADUs (RMC 3.10 as amended by Ord. 3217, June 17, 2025; 2025 Impact Fees Schedule). Rates index each January 1 — get the current figure from Development Services and cite the 50 percent cap if the quote looks high |
| 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 Redmond, where we have them — free, no obligation.
Get Redmond builder quotes →Permit fees in Redmond are Valuation-based (Residential Building Permit Fees, effective Feb. 1, 2025): a $300,000 detached ADU is about $4,069 permit + $2,645 plan review (65%) + $795 planning + $767 fire + 4% technology surcharge, roughly $8,600 before impact and utility fees. The review timeline is Not published for ADUs. State law requires a final decision within 65 days of the completeness determination for permits needing no public notice, with a partial fee refund if missed (RCW 36.70B.080(1)(d), (l)); Redmond's own time frames are in RZC 21.76.040 — ask the Permit Technician, with plan check: Standard building plan review at 65 percent of the permit fee, with planning ($794.94 new construction or $312.15 residential addition) and fire ($767.32 new residential construction) review lines; additional reviews after the third are $185 per hour (2025 residential fee table). For an ADU created inside an existing structure the Building Official may waive the IBC ceiling-height requirement where the structure met the code of its day (RZC 21.04.1110.C.5). Redmond's code still says detached ADUs must conform to all lot coverage restrictions (C.2.b), but RCW 36.70A.681(1)(j) requires the city to allow ADUs converted from existing structures, detached garages included, even where they violate current setback or lot coverage rules — cite it if you are converting a garage. Impact fees are Capped by state law at 50 percent of what the principal unit would pay (RCW 36.70A.681(1)(a)); RMC 3.10 itself carries no ADU line or exemption. For scale, the adopted single-family rates are $148.78 fire, $6,778.37 park and $5,972.00 school (plus a $65 school admin fee) per unit, and a transportation impact fee of $10,022.14 per Single-Family Detached unit ($7,604.20 in Centers) or $5,757.40 for Middle Housing ($4,368.37 in Centers), the category whose ITE basis includes ADUs (RMC 3.10 as amended by Ord. 3217, June 17, 2025; 2025 Impact Fees Schedule). Rates index each January 1 — get the current figure from Development Services and cite the 50 percent cap if the quote looks high. Pre-approved plans: None. The city's Residential Permits page (captured Feb. 2026) lists only the standard residential building, demolition and trade applications for an ADU, and no pre-approved ADU plan program appears there or in the zoning code. Neighbouring Kirkland runs a pre-approved detached ADU plan gallery; Redmond does not, so budget for a full plan set.
| 1-Bedroom Rent | $2,650-$2,850/month |
| 2-Bedroom Rent | $3,100-$3,350/month |
| Annual Rental Income (est.) | $33,000/year |
| Payback Period (est.) | 13.3 years |
| Short-Term Rental | Confirm with the City of Redmond before you list: the Redmond Municipal Code was not readable, and the zoning code limits only bed-and-breakfast inns (RZC 21.04.0100, note 2). Long-term letting is unrestricted |
| Overall ROI Estimate | 5-7% annual return |
A typical ADU in Redmond generates approximately $33,000 per year in rental income based on average 1-bedroom rents. At an average construction cost of $437,500, the estimated payback period is 13.3 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Redmond 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 Redmond: $100,000-$225,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $300,000-$450,000.
3. Pre-approved plans — available in Redmond, 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.
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