Can I build a backyard home in Duvall?
Since 2023, Washington law lets most city lots hold up to two more homes. Duvall writes its own rules on top. Here’s what the code says, in plain English — and a free report on what may fit on your lot.
What Duvall allows.
The headline standards. Tap any one for the full wording and the code section.
ADUs per lot2Full wording
2 — 'A maximum of two ADUs shall be permitted per principal dwelling unit. ADUs are exempt from the density requirements of the underlying zone.' (DMC 14.48.030(A), Ord. 1336)
Max size1,000 sq ft for a detached ADUFull wording
1,000 sq ft for a detached ADU — 'A detached ADU shall not exceed one thousand (1,000) square feet of gross floor area.' (DMC 14.48.030(E)); an ADU within an existing house or above a garage may be up to 1,500 sq ft (14.48.030(F)–(G))
Max height24 ft to the eaveFull wording
24 ft to the eave — 'A detached ADU shall be limited to a maximum building height of 24 feet as measured to the eave' (DMC 14.48.030(H); height measured per DMC 14.64.130); an ADU inside the principal dwelling may meet the zone height of 35 ft
Front setback10 ft street setback in R4 and R6 (same as the house)Full wording
Same as principal: 10 ft street setback in R4 and R6; garages 20 ft (DMC Tables 14.12.050.C, 14.12.070.C). ADUs must meet the underlying zone (DMC 14.48.030(C), (K))
Side setback5 ft minimum on any one side, 15 ft combined in R4 and R6Full wording
5 ft minimum on any one side, 15 ft combined in R4 and R6 (DMC Tables 14.12.050.C and 14.12.070.C, note 3); note 3 also says 'Side setbacks for accessory structures are five feet for all residential zones'
Rear setback15 ft in R4 and R6Full wording
15 ft in R4 and R6 (DMC Tables 14.12.050.C, 14.12.070.C); 5 ft from an alley; 'Detached accessory dwelling units may be located at a lot line if the lot line abuts a public alley' (DMC 14.48.030(C)(1); table note 12)
Lot coverage50% for lots of 7,200 sq ft or moreFull wording
50% for lots of 7,200 sq ft or more; 60% for smaller lots (6,000–7,199 sq ft in R4; 5,000–7,199 sq ft in R6) (DMC Tables 14.12.050.C, 14.12.070.C). Floor area ratio 50%, excluding garages and basements; the ADU counts toward impervious surface and floor area limits (DMC 14.48.030(K))
Parking1 per ADU, on top of the house’s spacesFull wording
1 space per ADU, in addition to the primary unit's spaces (DMC 14.48.030(I); Table in DMC 14.44.040(I): 'Single-family accessory dwelling unit (ADU) | 1 per unit')
Where a city figure reads stricter than the state floor (RCW 36.70A.681), the floor may control — the report flags it for your parcel.
Living there, selling it, plans, time and fees.
Each answer is the code’s own wording, with the section it comes from. “Not published yet” means the city hasn’t posted a figure — the report asks the city, not the internet.
Are backyard homes allowed?
Yes — 'Two ADUs are permitted as an accessory use to a principal dwelling unit in the R4, R4.5, R6, R8, R12, R20, and MU12 zones' (DMC 14.48.020) and 'ADUs may be attached to or detached from, the principal unit' (DMC 14.48.030(C), Ord. 1336)
Minimum lot size
None for an ADU; zone minimum applies to new lots: R4 6,000 sq ft, R6 5,000 sq ft (DMC Tables 14.12.050.C, 14.12.070.C)
Do you have to live there?
No — DMC Chapter 14.48 (Ord. 1336, June 5, 2025) has no owner-occupancy requirement
Can it be sold on its own?
Yes — 'ADUs may be subdivided or otherwise segregated in ownership from the primary dwelling unit' and condo sale 'may not be prohibited' (DMC 14.48.030(D)); the owner must notify the city 60 days before selling an ADU (14.48.040(B))
Pre-approved plans
None found
How long the city takes
Not published
Impact fees
ADUs pay 50% — 'Accessory Dwelling Units (ADUs) shall be subject to an impact fee equal to fifty percent (50%) of the impact fee applicable to the primary dwelling unit on the site, unless otherwise exempt under state law.' (DMC 14.58.060(C), Ord. 1344, Dec. 2, 2025); amounts set by fee resolution (DMC 14.48.045)
Plans Duvall has already approved.
A pre-approved plan skips the design review: Duvall has already checked the drawings, so the permit review is about your lot.
Loading the plans…
Pictures are the official pages’ own. A pre-approved plan is not a permit: the city still reviews your site.
The code is half the answer. Your parcel is the other half.
Lines and easements
Where the lot lines really are, which setbacks apply on each side, and whether a utility or access easement takes the corner you had in mind.
Critical areas and slope
Steep slopes, wetlands and streams come with buffers that no citywide number shows. The report reads the county’s maps for your parcel.
Sewer, septic, water, trees
Whether sewer reaches the lot or it’s on septic, where the water service is, and which trees a city protects — the things that decide where a unit can actually go.
What Duvall allows, what could fit on your lot, and a planning cost range. If something won’t fit, the report says so — and shows what might.
Where this page comes from.
Read from the Duvall municipal code and the city’s own pages on November 5, 2026. The same table feeds the HousUp report, so the report and this page never disagree. Cities amend their codes; before you design anything, confirm the current wording with the city.
8 sources, read November 5, 2026
- www.zoneomics.com/code/duvall-WA/chapter_26 (DMC 14.48)
- www.zoneomics.com/code/duvall-WA/chapter_7 (DMC 14.12)
- www.zoneomics.com/code/duvall-WA/chapter_24 (DMC 14.44)
- www.zoneomics.com/code/duvall-WA/chapter_31 (DMC 14.58)
- www.duvallwa.gov/269/Permits
- www.duvallwa.gov/536/Zoning-Code-Amendments
- official code https://library.municode.com/index.aspx?clientId=16325 (not readable by automated tools)
- RCW 36.70A.681 — the state floor for accessory dwelling units
Find out what your property could become.
Type your address. Within a few hours: what Duvall allows, what could fit, and a planning cost range. Free, no obligation.