Zoning & Size Limits
| Requirement | Princeton, NJ | Montclair, NJ |
|---|
| Allowed Zones | All residential districts where single-family dwellings are | R-O, R-O(a), R-1 and R-2 zones, on lots containing one- or t |
| Max Size (Detached) | 800 sq ft or 25% of the principal dwelling's total floor area, whichever is greater; +5% total floor area if the ADU is fully accessible under NJ's Barrier Free subcode; 1,000 sq ft or 30% if deed-restricted to low/moderate-income occupancy (Ord. 2024-32) | 300-800 sq ft, and no more than 40% of the habitable area of the principal building, whichever is less; no more than 3 rooms excluding kitchen and bathroom; detached ADUs must be located in the rear yard |
| Max Size (Attached) | Same standard as detached — 800 sq ft or 25% of principal floor area, whichever is greater; attached ADUs must use the same exterior materials and colors as the main house | Same standard — 300-800 sq ft and no more than 40% of the principal building's habitable area; may be part of an expanded or remodeled dwelling |
| Max Height | Detached ADUs follow the accessory-structure bulk | Detached ADUs follow accessory-building standards; |
| Parking Required | No additional parking for ADUs with 2 habitable rooms; 1 add | At least 1 off-street parking space required for the ADU |
| Owner Occupancy | Not required — Ordinance 2020-16 expressly eliminated Prince | Required — the property owner must occupy either the primary |
Setback Requirements
| Setback | Princeton, NJ | Montclair, NJ |
|---|
| Rear Setback | Per the accessory-structure setbacks of the underlying district — confirm with the Princeton Planning Department; detached ADUs must be at least 5 ft from the habitable portion of the main house | Accessory-building setbacks of the underlying zone apply — confirm with the Montclair Department of Planning & Community Development |
| Side Setback | Per the accessory-structure setbacks of the underlying district — confirm with the Princeton Planning Department | Accessory-building setbacks of the underlying zone apply — confirm with the Montclair Department of Planning & Community Development |
| Front Setback | No separate street-facing external entrance is all | Detached ADUs must be in the rear yard (not permit |
Permits & Timeline
| Detail | Princeton, NJ | Montclair, NJ |
|---|
| Permit Timeline | Confirm with the Princeton Zoning Office — no published ADU-specific timeline | Confirm with the Montclair Department of Planning & Community Development — no published ADU-specific timeline |
| Permit Fees | Confirm with the Princeton Zoning Office and Building Department — zoning permit plus UCC construction permit fees scale with project value | An ADU zoning permit fee applies (see the township's ADU zoning permit application); confirm the current amount and construction permit fees with the Planning Department |
| Impact Fees | No California-style ADU impact fees; sewer connection charge | No California-style ADU impact fees; sewer connection charge |
| Pre-Approved Plans | None offered as of July 2026 | None offered as of July 2026 |
Construction Costs
| Cost | Princeton, NJ | Montclair, NJ |
|---|
| Avg Build Cost | $180,000-$350,000 | $175,000-$325,000 |
| Cost Per Sq Ft | $250-$400 | $225-$375 |
| Garage Conversion | $70,000-$150,000 | $65,000-$150,000 |
| Prefab ADU | $130,000-$260,000 installed | $125,000-$250,000 installed |
Rental Income Potential
| Rental | Princeton, NJ | Montclair, NJ |
|---|
| 1BR Avg Rent | $2,400-$2,900/mo | $2,200-$2,800/mo |
| 2BR Avg Rent | $3,000-$3,500/mo | $2,800-$3,500/mo |
| Short-Term Rentals | The ADU must be used 'only for residential purposes for one | Not addressed in the township's ADU summary — confirm short- |
| Est. ROI | 6-9% gross annual return (long-term rental, before taxes and financing) | 7-10% gross annual return (long-term rental, before taxes and financing) |
Which City Is Better for ADUs?
Princeton scores 8/10 while Montclair scores 6/10 on our ADU-friendliness index.
Princeton edges ahead overall. Both cities offer viable ADU development opportunities — the best choice depends on your specific property, budget, and goals.
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