Build costs, cost per square foot, garage conversions and rents across 4 New Jersey cities, from each city’s own cost guide.
Building an ADU in New Jersey costs $160,000–$400,000 all-in across the 4 cities we cover (2026), or about $200–$450 per square foot. The middle of the 4 city ranges below sits around $293,750. Converting an existing garage runs $60,000–$200,000.
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| City | Typical build cost | Cost per sq ft | Garage conversion | 2-BR rent |
|---|---|---|---|---|
| Jersey City | $200,000-$400,000 | $250-$450 | $70,000-$200,000 | $2,500-$4,200/mo |
| Montclair | $200,000-$400,000 | $250-$450 | $95,000-$200,000 | $2,900-$3,400/mo |
| Princeton | $200,000-$375,000 | $275-$450 | $95,000-$170,000 | $2,900-$3,500/mo |
| Trenton | $160,000-$300,000 | $200-$375 | $60,000-$170,000 | $1,750-$2,250/mo |
Each figure is the city’s own cost guide; click a city for what is included, permit fees and the sources behind it.
Across the 4 New Jersey cities we cover, building a new ADU runs $160,000 to $400,000 all-in, depending on the city, size and finish. The middle of the city ranges sits around $293,750. Trenton has the lowest published range ($160,000-$300,000) and Jersey City the highest ($200,000-$400,000).
$200 to $450 per square foot across the 4 New Jersey cities we cover. Smaller units cost more per square foot, because the kitchen and bathroom are the expensive rooms.
Usually. Converting an existing garage runs $60,000 to $200,000 in the New Jersey cities we cover, against $160,000 to $400,000 for a new detached unit, because the foundation, walls and roof already exist.
A two-bedroom unit rents for about $1,750 to $4,200 a month across these cities. Each city's cost page shows its own rent figure and source.
Yes. An ADU is a home, so it needs a building permit, and the zoning rules, fees and review times are set city by city. Our New Jersey ADU laws page compares them.
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