Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Building an ADU in Cambridge costs between $210,000-$420,000 for new construction, with per-square-foot costs averaging $220-$440. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $105,000-$230,000, while prefab/modular ADUs fall in between at $160,000-$340,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | $3,500-$5,500 |
| Impact Fees | $1,500-$2,500 |
| 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 |
Permit fees in Cambridge are $3,500-$5,500. The review timeline is 60-90 days, with plan check taking approximately 3-4 weeks. Impact fees are $1,500-$2,500. Pre-approved plans: Not available.
| 1-Bedroom Rent | $1,900-$2,500/mo/month |
| 2-Bedroom Rent | $2,300-$3,400/mo/month |
| Annual Rental Income (est.) | $26,400/year |
| Payback Period (est.) | 11.9 years |
| Short-Term Rental | Not permitted |
| Overall ROI Estimate | 5-7% annual return |
A typical ADU in Cambridge generates approximately $26,400 per year in rental income based on average 1-bedroom rents. At an average construction cost of $315,000, the estimated payback period is 11.9 years — before accounting for property value appreciation, which typically adds 20-35% to home value.
1. Garage conversions save 40-60% vs new construction since the shell already exists. Average cost in Cambridge: $105,000-$230,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $160,000-$340,000.
3. Pre-approved plans (Not available) can save $3,000-$10,000 in design costs and 2-3 months in review time.
4. State grants — California's CalHFA program offers up to $40K. Check your state for available programs.
5. Get multiple bids — ADU contractor pricing varies 20-40% for the same project. We recommend getting at least 3 quotes.
Compare prices from pre-screened ADU contractors in your area. Free, no-obligation estimates.
Find ADU Contractors →