How Much Does an ADU Cost in Redmond, WA?

Construction Cost Breakdown

Building an ADU in Redmond costs between $255,000-$460,000 for new construction, with per-square-foot costs averaging $310-$510. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $125,000-$255,000, while prefab/modular ADUs fall in between at $185,000-$355,000.

Permit Costs & Timeline

Permit fees in Redmond are Confirm current building permit and plan review amounts with Redmond Development Services at 425-556-2494 — the fee schedule is not part of the zoning code and the city's fee page could not be retrieved for this entry. The review timeline is Confirm with Redmond Development Services at 425-556-2494 — no ADU-specific review timeline is published in the zoning code, and the city's own permit pages could not be retrieved for this entry (www.redmond.gov blocks automated access). Redmond adopted Ordinance 3174 in 2024 to conform its permit review procedures to Washington's SB 5290 permit-timeline law, so statutory review clocks apply; ask which category your application falls into, with plan check: Standard building plan review; no ADU-specific plan check process appears in the zoning code. Where an ADU is created inside an existing structure, expect the Building Official to look at the ceiling-height waiver at RZC 21.04.1110.C.6. Note that Redmond's code does not itself carry the state's conversion protection — RCW 36.70A.681(1)(j) requires a city to allow ADUs converted from existing structures, detached garages included, even where they violate current code requirements for setbacks or lot coverage, while RZC 21.04.1110.C.2.b still says detached ADUs "must each conform to all lot coverage restrictions." If you are converting a garage that does not meet today's setbacks, cite the statute. Impact fees are Capped by state law at 50 percent of the impact fees that would be imposed on the principal unit: "The city or county may not assess impact fees on the construction of accessory dwelling units that are greater than 50 percent of the impact fees that would be imposed on the principal unit" (RCW 36.70A.681(1)(a)). For scale, Redmond's adopted schedules for a single-family residence are $148.78 fire, $6,778.37 park and $5,972.00 school per housing unit, plus a transportation impact fee of $10,022.14 per dwelling unit for Single-Family Detached ($7,604.20 in Centers) or $5,757.40 for Middle Housing ($4,368.37 in Centers) (Redmond Municipal Code 3.10, as amended by Ordinance 3217, approved June 17, 2025). Which land-use category Redmond applies to an ADU is not stated in the schedule — ask Development Services, and cite the 50 percent cap if the quote looks high. Pre-approved plans: None found in a City of Redmond source as of September 1, 2026. Neighbouring Kirkland runs a pre-approved detached ADU plan gallery; no equivalent Redmond programme appears in the zoning code, and the city's own pages could not be retrieved for this entry. Confirm with Planner on Call at 425-556-2494 before assuming you must pay for a full custom set.

Rental Income & ROI

A typical ADU in Redmond generates approximately $28,500 per year in rental income based on average 1-bedroom rents. At an average construction cost of $357,500, the estimated payback period is 12.5 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).

Ways to Reduce ADU Costs in Redmond