Redmond ADU and detached ADU rules
Redmond ADU and DADU rules, including the affordable-housing payment
Redmond allows two ADUs or tiny homes on a residential lot and gives neighborhood-residential DADUs compact three-foot side and five-foot rear yards. The less obvious constraints are just as important: all new dwellings, including new attached and detached ADUs, need sprinklers, and neighborhood-residential projects can owe an affordable-housing payment on every square foot of net-new floor area.
Reviewed August 14, 2026 against adopted city code and official city guidanceQuick definitions. An accessory dwelling unit (ADU) is a complete additional home on the same property. A detached ADU (DADU) is in its own building. FAR or GFA limits how much enclosed floor area the property may contain.
Bottom line
What the current rules mean
A standard ADU may contain up to 1,000 square feet. In the NR zone, a principal home plus two ADUs is a three-unit project with a 7,500-square-foot total GFA allowance and can qualify for 60 percent lot coverage on a lot no larger than 18,000 square feet; the base height is 38 feet, with 10-foot front, three-foot side, five-foot rear and five-foot building-separation standards. Other zones have different tables.
What is allowed on one lot
Redmond allows up to two ADUs or tiny homes per residential lot, subject to the zone's allowed-use and development standards. An ADU may be inside or attached to the primary dwelling or in a detached structure. A tiny home is limited to 400 square feet.
- Two attached or internal ADUs.
- One attached and one detached ADU.
- Two detached ADUs or tiny homes where the zone, unit count, GFA, coverage, separation, access and utilities allow them.
- A separate attached or detached unit lot through the current unit-lot subdivision process; stacked units cannot use that route.
Official sources: RZC 21.04.1110: accessory dwelling units · Redmond Ordinance 3261 · RCW 36.70A.681: limits on local ADU regulation
Size, height, setbacks, and site capacity
- Maximum size
- A standard ADU may contain up to 1,000 square feet. The Administrator may approve more where it occupies an entire floor of the primary dwelling. On a site larger than 10,000 square feet, an increase may also be approved when the ADU is affordable or provides another accepted public benefit.
- Height
- A DADU uses the underlying zone's dwelling height, not the 22-foot limit for an ordinary non-ADU accessory structure. The neighborhood-residential base height is 38 feet. Roof, grade, shoreline and other zone conditions still apply.
- Setbacks
- In the NR zone, current base yards are 10 feet from the front and side street, three feet from an interior side, five feet from the rear, two feet from an alley, and 35 feet from Lake Sammamish; building separation is five feet. The DADU-specific rule permits immediate abutment of a public alley or right-of-way. Other zones use their own tables, and accessory buildings are generally prohibited in the front yard except for narrow garage conditions.
- FAR, lot coverage, or impervious area
- In NR, impervious area is limited to 70 percent and base lot coverage to 50 percent. Coverage can increase to 60 percent only when the lot is no larger than 18,000 square feet and contains at least three dwellings. Redmond uses a total-GFA cap rather than FAR in NR: 4,500 square feet for one unit, 6,000 for two, 7,500 for three, 9,000 for four, then 1,500 more per unit. The accessory structure footprint is also limited to 60 percent of the principal dwelling's ground-floor living footprint, excluding its garage.
Official sources: RZC 21.04.1110: accessory dwelling units · RZC 21.08.200: neighborhood residential standards · RZC 21.08.300: neighborhood residential placement
Parking, occupancy, renting, and separate sale
- Parking
- The current Redmond parking table requires zero spaces for an ADU and sets no ADU parking maximum.
- Owner occupancy
- Redmond has no current owner-occupancy requirement. An old deed-restriction sheet citing repealed RZC 21.08.220 is obsolete.
- Short-term rental
- A stay under 30 nights requires Redmond's business license and safety-checklist process effective January 1, 2026. Long-term rental remains subject to general landlord, business and private restrictions.
- Separate sale
- Current code does not bar segregated ownership. A unit-lot subdivision can create separate attached or detached unit lots, but not stacked-unit lots; condominium, title and subdivision requirements remain separate from the ADU building permit.
Official sources: RZC 21.40.010: parking table · Redmond short-term rental program · RZC 21.74.030: unit-lot subdivisions
Utilities, fire access, and the permit path
An attached or detached ADU may share the principal dwelling's Redmond water meter when ownership is the same; otherwise a separate meter is required. Domestic and sprinkler service may be combined or separate. Side-sewer arrangements, capacity, acknowledgements, utilities and fees depend on ownership, serving district and configuration.
- Confirm the zone, allowed use, lot area, existing legal units and structures, shoreline/critical areas, alley or right-of-way, title and application vesting.
- Count the proposed total dwellings before calculating NR total GFA and 50- or 60-percent coverage; also test the accessory-structure footprint cap, impervious area, yards, separation and height.
- Design the required residential sprinkler and coordinate fire access, flow, water meter/service and side-sewer capacity early.
- Calculate the neighborhood-residential affordable-housing payment from net-new floor area and the applicable vesting year, then request a City project estimate for impact and permit fees.
- Apply through Redmond's permit system with coordinated building, trade, fire sprinkler, utility, clearing/grading, site, tree, critical-area and storm documents.
Official sources: Redmond residential permits · Redmond residential sprinkler ruling · Redmond Ordinance 3255: water and sewer service · Redmond development-services fees
Rules that can change the answer for one property
A citywide ADU allowance does not prove that a detached unit fits on a particular lot. Resolve these items before buying plans or fixing the DADU location.
- All new Redmond dwellings, expressly including newly constructed attached and detached ADUs, require residential fire sprinklers.
- The NR affordable-housing payment applies to all net-new residential GFA, including additions, garages and ADUs; vesting year can double the per-square-foot rate.
- The published impact-fee table's 'middle housing including ADU' transportation row may exceed the statutory 50-percent ADU cap; obtain the City's project-specific statutory adjustment instead of summing rows.
- A principal home plus two ADUs changes the NR total-GFA and possibly the lot-coverage tier, so the proposed unit count must be modeled before declaring a fit.
- Significant and landmark trees, critical root zones, wetlands, streams, Lake Sammamish shoreline, geologic hazards, flood areas and critical-aquifer restrictions can control the footprint or construction method.
Official sources: Redmond affordable-housing payment information · Redmond tree-removal guidance · Redmond environmental actions · Redmond 2026 impact-fee schedule
Prepared for a future address check
What a reliable DADU feasibility screen must verify
Redmond's screen must treat total dwelling count as an input to NR GFA and coverage, then add the accessory-footprint cap, impervious area, yards, separation, height, trees, critical areas, utilities, mandatory sprinklers and the affordable-housing payment.
Confirm the address is actually governed by Redmond and select the correct base-zone standards.
Count the principal dwelling, existing legal ADUs, middle-housing units, and the proposed attached or detached configuration.
Use legal lot lines, front/rear designation, alleys, access easements, and existing structures rather than a tax-map rectangle.
Test the ADU against the rules that apply locally: FAR or GFA, building or lot coverage, impervious or hard surface, and landscaping.
Screen critical areas and buffers, shorelines, slopes, flood hazards, significant trees, drainage, and recorded easements.
Verify water, sewer or septic, fire flow, hydrant and apparatus access, power, meters, and trench routes.
The engine must overlay uncodified Ordinance 3261, avoid the repealed owner-occupancy handout, and route public-benefit size exceptions, impact-fee caps, separate ownership, fire-service design, CARA dewatering and vesting to manual review.
Do not rely on the older rule
Two City PDFs remain risky: the old deed-restriction sheet cites a repealed owner-occupancy section, and an older accessory-structure handout uses superseded height language. Ordinance 3261, adopted June 2, 2026, is also still pending codification, so it must be overlaid on the online code.
Primary sources
Official Redmond and Washington references
These are the sources used for this guide. Check them again before filing because ordinances, fee schedules, and permit forms can change.
A practical first-pass checklist
- 1
Confirm the parcel is inside Redmond city limits and identify its current zone.
- 2
Map the principal home, lot lines, easements, trees, utilities, driveway, critical areas, and buffers on one current survey.
- 3
Test the ADU footprint against setbacks, height, floor-area or coverage limits, hardscape, parking, and construction access.
- 4
Ask the utility providers to confirm water, sewer, power, meter, side-sewer, and capacity requirements before fixing the design.
- 5
Have the city confirm the complete land-use, building, fire, right-of-way, tree, and utility permit list in writing.