Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Bellevue ADU cost →Building an ADU in Bellevue costs between $325,000-$550,000 for new construction, with per-square-foot costs averaging $400-$650. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $100,000-$225,000, while prefab/modular ADUs fall in between at $300,000-$450,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | Fees are set by the 2026 fee ordinance (Ord. 6879): a plan-review deposit at submittal and an inspection deposit at issuance, charged at the stated hourly rate with monthly invoices for overage. Use the City's Permit Fee Estimator (permitfeeestimator.bellevuewa.gov) for a figure |
| Impact Fees | Transportation impact fee: single-family rate $8,185 per dwelling from Jan. 1, 2026 ($8,430 from Jan. 1, 2027, Ord. 6888); state law caps an ADU at 50% of the principal unit's fee (RCW 36.70A.681(1)(a)), so expect about $4,092 at most - the 2026 schedule has no ADU line, confirm the category with Transportation Development Review (425-452-4236). School impact fee: only in the Issaquah ($4,728 per single-family unit) and Renton ($1,003) school district parts of the city, and an ADU pays 50% (BCC 22.18.100, Ord. 6852); no school impact fee in the Bellevue School District. ADUs are exempt from street frontage improvements (BCC 14.60.110.G). Water and sewer connection charges apply separately - see Utilities Permit Fees |
| Site Prep & Foundation | $10,000 – $35,000 |
| Framing & Structure | $15,000 – $45,000 |
| Plumbing | $8,000 – $20,000 |
| Electrical | $5,000 – $15,000 |
| HVAC | $3,000 – $8,000 |
| Interior Finishes | $15,000 – $40,000 |
Quotes for the same ADU commonly vary 20–40% between builders. We pass your request to up to 5 local builders serving Bellevue, where we have them — free, no obligation.
Get Bellevue builder quotes →Permit fees in Bellevue are Fees are set by the 2026 fee ordinance (Ord. 6879): a plan-review deposit at submittal and an inspection deposit at issuance, charged at the stated hourly rate with monthly invoices for overage. Use the City's Permit Fee Estimator (permitfeeestimator.bellevuewa.gov) for a figure. The review timeline is The City publishes no target review time for a BS permit; plan review is billed hourly against a submittal deposit, so timing follows the review queue. Ask Permit Processing (425-452-6800) for the current first-review estimate, with plan check: Standard building plan review by Development Services under the BS permit; reviewers charge hours against the deposit, and the middle-housing amendments removed design-review and design-matching controls for ADUs (Ord. 6746; RCW 36.70A.681(1)(h)). A pre-application meeting is optional. Impact fees are Transportation impact fee: single-family rate $8,185 per dwelling from Jan. 1, 2026 ($8,430 from Jan. 1, 2027, Ord. 6888); state law caps an ADU at 50% of the principal unit's fee (RCW 36.70A.681(1)(a)), so expect about $4,092 at most - the 2026 schedule has no ADU line, confirm the category with Transportation Development Review (425-452-4236). School impact fee: only in the Issaquah ($4,728 per single-family unit) and Renton ($1,003) school district parts of the city, and an ADU pays 50% (BCC 22.18.100, Ord. 6852); no school impact fee in the Bellevue School District. ADUs are exempt from street frontage improvements (BCC 14.60.110.G). Water and sewer connection charges apply separately - see Utilities Permit Fees. Pre-approved plans: None available yet. The council made a DADU and cottage pre-approved plans program a 2024-2026 priority; the March 10, 2026 study session laid out a three-phase program ending with up to 10 city-pre-approved plans sold at a set price, timed to the next state building code adoption (City Pre-Approved Plans page).
| 1-Bedroom Rent | $2,500-$3,200/month |
| 2-Bedroom Rent | $2,900-$3,750/month |
| Annual Rental Income (est.) | $34,200/year |
| Payback Period (est.) | 12.8 years |
| Short-Term Rental | No citywide ban identified. Stays under 30 days are regulated as 'short term stay uses' under LUC 20.20.800, which Ord. |
| Overall ROI Estimate | 5-8% gross rental yield on a $400,000-$550,000 detached build renting at $2,700-$3,500/mo, before vacancy, taxes and financing; conversions of existing space at $100,000-$225,000 yield roughly twice that |
A typical ADU in Bellevue generates approximately $34,200 per year in rental income based on average 1-bedroom rents. At an average construction cost of $437,500, the estimated payback period is 12.8 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Bellevue and varies by market (often less than build cost).
1. Garage conversions save 40-60% vs new construction since the shell already exists. Average cost in Bellevue: $100,000-$225,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $300,000-$450,000.
3. Pre-approved plans — available in Bellevue, which can save $3,000-$10,000 in design costs and 2-3 months in review time. See which cities offer pre-approved ADU plans.
4. State grants — California's CalHFA ADU grant (up to $40K) is currently paused; check calhfa.ca.gov/adu for status and your state for active programs.
5. Get multiple bids — ADU contractor pricing varies 20-40% for the same project. We recommend getting at least 3 quotes.
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