Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Trenton ADU cost →Building an ADU in Trenton costs between $140,000-$260,000 for new construction, with per-square-foot costs averaging $220-$340. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $55,000-$120,000, while prefab/modular ADUs fall in between at $110,000-$210,000 installed.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | Confirm with the Trenton Construction Office — zoning permit plus UCC construction permit fees, which scale with project value |
| Impact Fees | No California-style ADU impact fee. Sewer/water connection charges may apply — confirm with Trenton Water Works and the Construction Office. |
| 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 Trenton — no obligation.
Get Trenton builder quotes →Permit fees in Trenton are Confirm with the Trenton Construction Office — zoning permit plus UCC construction permit fees, which scale with project value. The review timeline is Confirm with the Trenton Division of Planning and the Construction Office — no ADU-specific timeline is published, with plan check: Standard New Jersey Uniform Construction Code review. Accessory structures count toward the district's maximum impervious surface and building coverage (§ 315-9.4A.4), so coverage is checked at zoning review.. Impact fees are No California-style ADU impact fee. Sewer/water connection charges may apply — confirm with Trenton Water Works and the Construction Office.. Pre-approved plans: None published.
| 1-Bedroom Rent | $1,545/month |
| 2-Bedroom Rent | $1,950/month |
| Annual Rental Income (est.) | $18,540/year |
| Payback Period (est.) | 10.8 years |
| Short-Term Rental | The ordinance does not itself authorise short-term rental of an ADU; owner-occupancy of one unit is required either way. Confirm short-term rental rules with the City of Trenton before counting on nightly income. |
| Overall ROI Estimate | 7-10% gross annual return on a long-term rental, before taxes and financing. Rent figures are HUD FY2026 Fair Market Rents for the Trenton-Princeton NJ MSA, which is a 40th-percentile measure — a newly built ADU typically rents above it. |
A typical ADU in Trenton generates approximately $18,540 per year in rental income based on average 1-bedroom rents. At an average construction cost of $200,000, the estimated payback period is 10.8 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Trenton 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 Trenton: $55,000-$120,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $110,000-$210,000 installed.
3. Pre-approved plans — Trenton does not offer a pre-approved/standard ADU plan program yet, so budget for custom architectural plans (typically $3,000-$15,000). 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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