Redmond ADU and detached ADU rules
Can I build an ADU or DADU in Redmond?
Redmond generally allows up to two ADUs or tiny homes, but the unit count changes the Neighborhood Residential GFA and coverage calculation. A new attached or detached ADU also needs residential sprinklers, and net-new floor area can trigger affordable-housing and impact fees. Check these costs and site constraints before selecting a plan.
Quick 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.
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Common homeowner questions
Answers to common Redmond ADU questions
Can I build an ADU or DADU on my Redmond property?
Often, yes. Redmond allows up to two ADUs or tiny homes on a residential lot, but zoning, existing units, total GFA, lot coverage, impervious area, trees, critical areas, utilities, access, and required sprinklers determine whether the project fits.
How large can a Redmond ADU be?
A standard ADU may contain up to 1,000 square feet; a tiny home is capped at 400 square feet. A narrow whole-floor exception or an approved public-benefit proposal on a site larger than 10,000 square feet may allow more.
What setbacks apply to a Redmond DADU?
In the Neighborhood Residential zone, the current base yards are 10 feet from the front and side street, three feet from an interior side, five feet from the rear, and two feet from an alley, with five feet of building separation. Other zones, shorelines, critical areas, easements, and fire access can change the result.
Do new Redmond ADUs require sprinklers and parking?
New attached and detached ADUs require residential fire sprinklers. Redmond's current parking table requires zero off-street spaces specifically for an ADU, although access and utility design still need to work.
What extra Redmond ADU costs should I plan for?
Neighborhood Residential projects can owe an affordable-housing payment of $15 or $30 per square foot of net-new floor area depending on vesting and program rules. Add permit, utility, fire-sprinkler, and project-specific impact charges, and ask the City to apply the statutory ADU impact-fee cap rather than simply summing the published rows.
How can I tell whether an ADU will fit on my Redmond lot?
Use Redmond's Property Viewer to confirm the parcel and mapped conditions, then calculate dwelling-count-based GFA and coverage, accessory-building footprint, impervious area, setbacks, trees, hazards, utilities, sprinklers, and fees. A feasibility result should test all of them against the same concept.
Official sources: RZC 21.04.1110: accessory dwelling units · Redmond Ordinance 3261 · RZC 21.08.200: neighborhood residential standards · Redmond Property Viewer · RZC 21.08.300: neighborhood residential placement · Redmond residential sprinkler ruling · RZC 21.40.010: parking table · Redmond affordable-housing payment information · Redmond development-services fees · Redmond 2026 impact-fee schedule · Redmond Ordinance 3255: water and sewer service · Redmond tree-removal guidance · Redmond environmental actions
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
How much room the property may have for an ADU
- 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
Make the most of the lot
ADU allowances worth checking before you design
An ADU can be a home for family, a rental, or a way to use space you already have. Before ruling it out, check the allowances below. They are specific code provisions, not a way around permits.
Allowance review: September 19, 2026. Confirm your parcel, application date, and proposed layout with the city before paying for detailed plans.
More homes can raise the total floor-area limit
In the Neighborhood Residential (NR) zone, Redmond uses a total gross floor area (GFA) limit rather than FAR. GFA is the counted floor area across the property. A legal ADU adds to the dwelling count, whether attached or detached.
| Homes on the lot | Total GFA limit |
|---|---|
| One house | 4,500 sq ft |
| House + one ADU | 6,000 sq ft |
| House + two ADUs | 7,500 sq ft |
Example: A 4,300 sq ft counted house-and-garage total plus a 1,000 sq ft ADU is 5,300 sq ft. That is below the two-home ceiling. It does not prove the footprint fits.
Coverage can increase too. NR building coverage rises from 50% to 60% when the lot is no larger than 18,000 sq ft and contains at least three dwellings. One house plus one ADU is not enough. Impervious coverage remains a separate test.
Redmond NR floor-area and coverage tables ↗
Stairs and some open areas do not count, but garages and basements do
RZC 21.16.200(E) excludes stairwells, second-story atriums, vent and elevator shafts, courts, lobbies, unroofed areas, and roofed areas open on at least two sides from NR GFA. It also excludes accessory structures smaller than 200 sq ft.
Garages and below-grade floors count. Do not borrow Bellevue or Kirkland exemptions. A second-story atrium exclusion is not a credit for the room below it. A structure under 200 sq ft is not automatically an exempt or permitted tiny home.
Ask your architect for an area plan that identifies each exclusion. These are rules for the whole property's GFA calculation. Do not automatically reuse them to increase the ADU's own size limit.
Redmond NR measurement rules, subsection E ↗
A larger ADU is possible in two specific cases
The usual ADU limit is 1,000 sq ft. The Administrator may approve more when an ADU uses an entire floor of the main home. On a site larger than 10,000 sq ft, an increase may also be approved for an affordable ADU or an accepted public benefit. Neither is automatic.
The DADU rule also permits placement at a lot line adjoining a public alley or right-of-way. Ask the city to confirm the exact boundary and fire, access, easement, and other applicable requirements before using a zero setback.
Redmond ADU size exceptions and placement rules ↗
Compare three layouts before choosing one
- Inside the house. Could an existing floor become a separate home without adding a footprint?
- Inside an existing outbuilding. Can it be converted safely, and what parking or utility work would that trigger?
- A new DADU. Does its footprint fit after coverage, yards, trees, access, and drainage are checked?
Keep the unit-size limit, total counted floor area, building coverage, and impervious area as separate calculations. Passing one does not mean the others pass. A nominal second unit must be a real, permitted home, not just a label on a bedroom.
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
Address-level ADU feasibility
What to check before assuming a detached ADU will fit
Count the existing and proposed homes before checking NR floor area and coverage. Then check building footprint, paving, yards, height, trees, site hazards, utilities, sprinklers, and fees.
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.
Use the current code, which now includes Ordinance 3261. Ask the City to confirm size exceptions, impact fees, separate ownership, fire-service design, groundwater restrictions, and the rules in effect for your application.
Do not rely on the older rule
The old deed-restriction sheet cites a repealed owner-occupancy section. An older accessory-structure handout uses superseded height language. The current online code now includes Ordinance 3261, codified in August 2026. Use its current ADU and NR tables rather than those older handouts.
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.
What to check first
- 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.
Practical worksheet
Put this guide to work
Worksheet updated . This is a planning example. Regulatory sources and data have their own dates.
Compare the configurations before picking a floor plan
A basement conversion, an attached addition and a detached backyard unit can have the same target living area but very different constraints. A conversion depends on the existing structure and usable headroom. A detached unit may create more utility trenching, access and tree conflicts. A pre-approved plan still needs a site-specific fit check.
- Option A: use existing space
- Ask the designer to evaluate structure, moisture, light, exits, fire separation and system capacity. Verify that the existing work is lawful rather than relying on a listing description.
- Option B: attach new space
- Check how the new area is counted with the primary home, how the roof and structure connect and whether occupied construction is practical.
- Option C: detach
- Test the permitted location, building separation, access, utilities, drainage and construction route. Include the whole property in coverage and tree calculations.
- Use and ownership
- Confirm the proposed rental duration, occupancy, addressing, utility arrangement and any separate-sale path under the current local rules. An ADU permit is not a completed subdivision or condominium process.
Request comparable budgets with the same inclusions: design, studies, permits, site work, utility upgrades, building work, taxes and contingency. A price for the prefabricated unit or shell is not the complete installed project cost.