ADU floor plans
300 to 1,200 sqft.
How to pick the right ADU size for your lot, household, and rental goal — with Washington code minimums, room-by-room area requirements, real Puget Sound cost and rent ranges, and the use-case scenarios we see most often. Pulled from 41 closed Golden State permits.
The six common ADU sizes
| Band | Sqft | Layout | BR | Fits on | Build $ | Rent |
|---|---|---|---|---|---|---|
| Micro Studio | 300–450 | Open plan, kitchenette, 3/4 bath | 0 (studio) | Tight urban lots (4,000–5,000 sqft) with strict setbacks | $165k–$235k | $1,450–$1,950 |
| Compact Studio / Junior 1BR | 451–600 | Separated sleeping alcove, full kitchen, full bath | 0–1 | Most R-zoned Seattle and Bellevue lots | $215k–$295k | $1,750–$2,250 |
| Standard 1-Bedroom | 601–800 | Separate bedroom + living + full kitchen + full bath | 1 | Standard 5,000–7,200 sqft Puget Sound lots | $265k–$355k | $2,050–$2,650 |
| Large 1BR / Compact 2BR | 801–1,000 | 1BR + den, or 2BR with shared bath | 1–2 | Lots ≥ 6,000 sqft, FAR-friendly zoning (LR1/RSL/R-5) | $315k–$420k | $2,400–$3,100 |
| Full 2-Bedroom | 1,001–1,200 | 2BR + 1.5 or 2 baths + full kitchen + living/dining | 2 | Lots ≥ 7,200 sqft, two-story DADU build envelope | $365k–$485k | $2,750–$3,500 |
| Maximum DADU (Two-Story) | 1,200 (HB 1337 cap) | 2–3BR, garage or storage on ground floor, living above | 2–3 | ≥ 7,500 sqft lots with 2-story height allowance (24–30') | $425k–$575k | $3,100–$4,000 |
Build cost = turnkey including site work, permit, design, finishes (2026 Puget Sound averages). Rent = current Zillow / Apartments.com saturated bands by Seattle / Eastside submarket.
Pick by what the unit is for
600–800 sqft, 1BR, single-story
Single-floor accessibility, separate bedroom for caregivers, full bath with grab-bar prep
700–900 sqft, 1BR or 1BR + den
Best $/sqft ROI in Puget Sound — saturates rental demand without overbuilding
450–600 sqft studio
Lowest construction cost; privacy without the full-residence overhead
500–700 sqft, 1BR with parking
Sweet spot for nightly rates vs. cleaning turnover cost
1,000–1,200 sqft, 2BR + 1.5 bath
Full secondary residence; sized to HB 1337 cap of 1,200 sqft
1,000–1,200 sqft, 2BR two-story
Appraisers value bedroom count + sqft; max DADU = max comp lift
Room-by-room area minimums
| Room | Required in | Min size | Notes |
|---|---|---|---|
| Bedroom (primary) | Studio + | 70 sqft | 7'-0" minimum any dimension; egress window required |
| Bedroom (secondary) | 2BR + | 70 sqft | Same egress + closet rules as primary |
| Living room | All | 120 sqft realistic | Code only requires 70 sqft, but smaller feels cramped |
| Kitchen | All | 40–60 sqft | Min 4' aisle clearance; full kitchen if used as ADU |
| Full bathroom | All | 35–45 sqft | 5' × 7' minimum for tub; 3' × 5' for shower-only |
| Half bath | 2BR + only | 18–25 sqft | Toilet + sink only; ≥ 30" clear in front of toilet |
| Closet (bedroom) | All | Width × 2' | Building code requires storage in each sleeping room |
| Mechanical / utility | All | 12–25 sqft | Water heater, HVAC, electrical panel access |
Washington code minimums
7'-0" in habitable rooms; 6'-8" in bathrooms, kitchens, hallways
Source: IRC R305.1 (adopted statewide via WA State Building Code)
Habitable rooms ≥ 70 sqft, with no horizontal dimension < 7'-0"
Source: IRC R304.1
Operable window with ≥ 5.7 sqft clear opening, sill ≤ 44" above floor
Source: IRC R310.1
Mechanical exhaust 50 CFM intermittent or 20 CFM continuous
Source: IRC M1507 / WSEC R403
Range hood 100 CFM intermittent or 25 CFM continuous, ducted outside
Source: WSEC R403.5 / IMC 505
Cities cannot cap DADUs below 1,000 sqft (most allow 1,000–1,200)
Source: RCW 36.70A.681 (HB 1337)
Cities may not impose minimum lot size for one ADU on a residential lot
Source: RCW 36.70A.681(2)(b)
Cannot be required within ½ mile of a major transit stop
Source: RCW 36.70A.681(2)(d)
Official code references
- WA State Building Code (SBCC) →
Adopted IRC, IBC, IMC, WSEC editions and amendments
- RCW 36.70A.681 — HB 1337 →
Statewide ADU minimums cities must allow
- IRC R304/R305 — Room sizes →
Habitable room area & ceiling height
- IRC R310 — Egress →
Bedroom emergency escape requirements
- WSEC Residential 2021 →
Washington energy code (insulation, ventilation, glazing)
Read next
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