Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Bellevue ADU cost →Building an ADU in Bellevue costs between $180,000-$380,000 for new construction, with per-square-foot costs averaging $200-$350. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $90,000-$190,000, while prefab/modular ADUs fall in between at $120,000-$280,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | Permit and plan review fees based on project valuation — Confirm with Bellevue Development Services |
| Impact Fees | School/transportation impact fees may apply; HB 1337 caps ADU impact fees at 50% of those for the principal unit — Confirm with Bellevue Development Services |
| 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. Get up to 3 free quotes from ADU builders serving Bellevue — no obligation.
Get Bellevue builder quotes →Permit fees in Bellevue are Permit and plan review fees based on project valuation — Confirm with Bellevue Development Services. The review timeline is Several weeks to a few months depending on review queue — Confirm with Bellevue Development Services, with plan check: Standard plan review; timing varies with queue — Confirm with Bellevue Development Services. Impact fees are School/transportation impact fees may apply; HB 1337 caps ADU impact fees at 50% of those for the principal unit — Confirm with Bellevue Development Services. Pre-approved plans: No city pre-approved plan library — Confirm with Bellevue Development Services.
| 1-Bedroom Rent | $2,500-$2,900/month |
| 2-Bedroom Rent | $3,100-$3,900/month |
| Annual Rental Income (est.) | $32,400/year |
| Payback Period (est.) | 8.6 years |
| Short-Term Rental | No citywide STR ban identified — Confirm current short-term rental licensing with the City of Bellevue |
| Overall ROI Estimate | 6-8% annual return |
A typical ADU in Bellevue generates approximately $32,400 per year in rental income based on average 1-bedroom rents. At an average construction cost of $280,000, the estimated payback period is 8.6 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: $90,000-$190,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $120,000-$280,000.
3. Pre-approved plans — Bellevue does not offer a pre-approved/standard ADU plan program yet, so budget for custom architectural plans (typically $3,000-$15,000).
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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