Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Trenton ADU cost →Building an ADU in Trenton costs between $160,000-$300,000 for new construction, with per-square-foot costs averaging $200-$375. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $60,000-$170,000, while prefab/modular ADUs fall in between at $120,000-$250,000 installed.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & Fees | $50 zoning permit (charged only when no other permit is required) and $75 for a written zoning determination (§ 315-19.4). Construction permit fees are 'as per City Code and defined under UCC' and scale with the work; get the current schedule from Technical Services. |
| Impact Fees | None in the LDO: Article 19 lists only application, escrow and administrative fees, with no development or impact fee for an added dwelling unit. Water and sewer connection charges for a new detached unit come from Trenton Water Works and the Construction Office; confirm them before pricing the job. |
| 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 Trenton, where we have them — free, no obligation.
Get Trenton builder quotes →Permit fees in Trenton are $50 zoning permit (charged only when no other permit is required) and $75 for a written zoning determination (§ 315-19.4). Construction permit fees are 'as per City Code and defined under UCC' and scale with the work; get the current schedule from Technical Services.. The review timeline is Not published. Neither the Division of Planning nor the Division of Technical Services publishes a zoning-permit or ADU review time; ask both when you file., with plan check: Standard NJ Uniform Construction Code plan review by the building, electrical, plumbing and fire subcode officials. At zoning review the ADU is checked against the district's building coverage (35-50%) and impervious surface (45-70%) caps in Table 4-1, which count accessory structures (§ 315-9.4A.4), and a detached unit's footprint against the house footprint (§ 315-9.4A.5).. Impact fees are None in the LDO: Article 19 lists only application, escrow and administrative fees, with no development or impact fee for an added dwelling unit. Water and sewer connection charges for a new detached unit come from Trenton Water Works and the Construction Office; confirm them before pricing the job.. Pre-approved plans: None published. The Division of Planning offers no ADU handout, pre-approved plan set or ADU-specific application form (checked September 2026)..
| 1-Bedroom Rent | $1,400-$1,800/month |
| 2-Bedroom Rent | $1,750-$2,250/month |
| Annual Rental Income (est.) | $19,200/year |
| Payback Period (est.) | 12.0 years |
| Short-Term Rental | The LDO does not address short-term rental of an ADU, and one unit must stay owner-occupied (§ 315-9.4B.2). Confirm rental registration and any short-term rules with the Division of Housing Inspections. |
| Overall ROI Estimate | 7-11% gross annual return on a long-term rental before tax and financing: $1,600-$2,000/mo against a $160,000-$300,000 build. HUD FY2027 SAFMRs are 40th-percentile rents; a new unit usually rents above them. |
A typical ADU in Trenton generates approximately $19,200 per year in rental income based on average 1-bedroom rents. At an average construction cost of $230,000, the estimated payback period is 12.0 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: $60,000-$170,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $120,000-$250,000 installed.
3. Pre-approved plans — available in Trenton, 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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