Everything homeowners ask about building an ADU in Redmond — answered with 2026 data.
Yes, ADUs are allowed in Permitted (P) in the Neighborhood Residential (NR), Neighborhood Multifamily (NMF), Neighborhood Mixed-Use (NMU), Citywide Mixed-Use (CMU), Marymoor Village Edge (MME), Downtown Edge (DTE), Downtown Core (DTC), Town Center (TWNC), Urban Recreation (UR) and RA-5 zones; not permitted in UMU, MMC, MMM, the Overlake zones, BP, MP, I or COS (RZC 21.04.0100, Residential Use Table, as amended by Ord. 3261). Standards: RZC 21.04.1110. Confirm your zone with Planner on Call, 425-556-2494 in Redmond, WA. The maximum size for a detached ADU is 1,000 sq ft: "The total square footage of an ADU shall not exceed 1,000 square feet" (RZC 21.04.1110.C.3.a) — exactly the floor RCW 36.70A.681(1)(f) sets. On a site over 10,000 sq ft the Administrator may allow more if the ADU is an affordable unit or a public benefit is provided (C.3.c). Watch the accessory-structure rule: accessory footprints may not exceed 60 percent of the house's ground-floor living area, excluding garage (RZC 21.04.1120.C.2.a). Attached ADUs can be up to Same 1,000 sq ft cap. Redmond has an ADU-friendliness score of 9/10. Check our full Redmond ADU rules page for complete zoning details.
ADU construction in Redmond typically costs $325,000-$550,000. The cost per square foot averages $400-$650. Garage conversions are more affordable at $100,000-$225,000, while prefab ADUs cost $300,000-$450,000. Permit fees add 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 to your budget. See our detailed Redmond ADU cost guide.
Detached ADUs in Redmond can be up to 1,000 sq ft: "The total square footage of an ADU shall not exceed 1,000 square feet". Attached ADUs are limited to Same 1,000 sq ft cap. Junior ADUs (JADUs) have a cap of Not a category in Washington — Redmond's code has no junior ADU. Its second small-unit type is the tiny home: it counts against the two-unit allowance, may not exceed 400 sq ft, and where in public view its trailer base must be fully screened by landscaping (RZC 21.04.1110.C.1, C.2.c and C.3.d). Maximum height is The height limit of the underlying zone — 38 ft base maximum in the Neighborhood Residential and NMU zones, 60 ft in NMF (Table 21.08.200.B). Ordinary accessory structures are capped at 22 ft, but RZC 21.04.1120.C.1 excepts "accessory structures that contain accessory dwelling units, which shall not exceed the height maximum of the underlying zone." State law separately bars any ADU roof-height limit below 24 ft unless the principal unit's own limit is lower (RCW 36.70A.681(1)(g)). You are allowed up to 2 ADUs per residential lot: "Two ADUs or tiny homes shall be allowed on each residential lot" on a qualifying lot.
Rear setback: 5 ft in the Neighborhood Residential zone, the same as the house (Table 21.08.300.A); accessory structures in NR and NMU "shall comply with the underlying setback regulations of the zone" (RZC 21.04.1120.C.5). The alley setback is 2 ft, and RZC 21.04.1110.C.2.b goes further: detached ADUs may be sited immediately abutting a lot line that abuts a public alley or right-of-way, overriding other setbacks — broader than RCW 36.70A.681(1)(i), which covers alleys only. Side setback: 3 ft side interior and 10 ft side street in the Neighborhood Residential zone, the same as the house (Table 21.08.300.A; RZC 21.04.1120.C.5); NMU is also 3 ft interior, NMF 15 ft. No minimum building separation applies to an accessory structure unless the building or fire code dictates one (RZC 21.04.1120.C.3). Zero-lot-line developments under RZC 21.16.200.D may vary. State law bars ADU setbacks more restrictive than the principal unit's (RCW 36.70A.681(1)(h)). Front setback: 10 ft in the Neighborhood Residential zone (Table 21.08.300.A). Accessory structures are prohibited in the front-yard setback, with a narrow exception for garages where lot width at the front street is under 50 ft, grades are steep, or compliance would impair pedestrian and vehicular safety (RZC 21.04.1120.C.4). RZC 21.08.300.A.2 allows only improvements under 30 inches above grade, fences, landscaping and the like in any setback — "No other structures, including accessory structures". Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
None, anywhere in Redmond. Table 21.40.010.D, Required Off-Street Parking, gives the accessory dwelling unit and the tiny home a ratio of "Dwelling unit (0, –)" in all three location columns — near frequent transit or in a TOD focus area, in a Center, and All Other Locations — while a detached house still needs 1.0 space in All Other Locations. That exceeds the state floor: RCW 36.70A.681(2)(a) only bars parking within a half-mile walk of a major transit stop. Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
Not required. RZC 21.04.1110 (as adopted by Ord. 3220 and amended by Ord. 3261) contains no owner-occupancy clause, no ban on renting the owner's unit and no recorded-covenant requirement; the repealed RZC 21.08.220.C.5 used to impose all three. The city could not reinstate them: RCW 36.70A.681(1)(b) bars requiring the owner of a lot with an ADU to reside in or occupy the ADU or another unit on the lot. Home businesses are allowed in both the ADU and the primary unit (RZC 21.04.1110.C.4). Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Redmond is typically 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. 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. Pre-approved plans availability: 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.
Average ADU rental income in Redmond: 1-bedroom units rent for $2,650-$2,850/month, 2-bedroom units for $3,100-$3,350/month. Short-term rentals: 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. Expected ROI: 5-7% annual return.
The minimum lot size for an ADU in Redmond is No ADU-specific minimum: RZC 21.04.1110 sets none, and RCW 36.70A.681(1)(e) requires the city to allow an ADU on any lot that meets the minimum lot size for the principal unit. The Neighborhood Residential zone's own standards are a 3,000 sq ft average minimum lot size, a 20 ft minimum lot frontage and 20 percent minimum open space (Table 21.08.200.B, as amended by Ord. 3261); lot coverage is 50 percent, or 60 percent on a lot of 18,000 sq ft or less with at least three dwelling units (note 8). This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Redmond, a garage conversion typically costs $100,000-$225,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.
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