Can I really sell my Princeton ADU separately from my main house?

Under specific affordability provisions in the ordinance, yes — Princeton is the only NJ town we are aware of that allows this. The unit must meet affordability and deed-restriction conditions. This is something we confirm against your specific lot in the Feasibility Study, since the rules vary by zone and lot configuration.

What size ADU can I build in Princeton?

Maximum size depends on your zone, your lot dimensions, and your existing impervious coverage. The ordinance sets size relative to the principal structure, with hard caps that vary by district. We pull your zone's specific limits and run the math against your lot in the Feasibility Study.

If Princeton allows ADUs by-right, why do I need a $750 Feasibility Study?

Town rules tell you whether ADUs are permitted somewhere in town. They do not tell you whether your specific lot can support one. The Feasibility Study answers: what zone are you in, what's your maximum ADU size given your existing impervious coverage, where can it sit given your setbacks, and is utility trenching feasible? An architect will charge $5,000+ to design something the township may reject. We answer the legality question first, in 5 days, for $750 — and the fee rolls 100% into your Permit-Ready Package if you proceed.

← NJ ADU Zoning

ADU Rules in Princeton, Mercer County

Permitted by-right

Yes — Princeton permits one ADU per lot by-right across most residential zones (R-A through R-H). It is among the most permissive ADU ordinances in New Jersey.

Princeton has the most homeowner-friendly ADU ordinance in New Jersey. The 2020 ordinance — refined through 2024 — permits one accessory dwelling unit per lot by-right across the R-A through R-H residential districts. Princeton is also the only NJ municipality we know of that allows ADUs to be sold separately from the principal dwelling under specific affordability provisions.

That said, by-right at the town level does not mean automatic at the lot level. Your specific zone, your existing lot coverage, your setbacks, and your utility constraints all still need verification before you commit to architect plans. Knowing Princeton allows ADUs is the easy part; knowing whether yours does — and what you can build — takes a feasibility study.

Permitted Zones

R-AR-BR-CR-DR-ER-FR-GR-H

Source: Ord. 2020-16 (amended through 2024)

Headline Restrictions

One ADU per lot
Owner-occupancy of one of the units required in most cases
Affordability provisions allow ADUs to be sold separately from the principal dwelling — a feature unique to Princeton
Standard setback, height, and lot-coverage rules still apply per zone

FAQ

Common questions about ADUs in Princeton.

Yes. Under Ord. 2020-16, one ADU per lot is a permitted use in R-A through R-H zones — meaning no variance, no conditional-use hearing, no Planning Board approval needed if you meet the ordinance's standards. You still need permits and inspections, but you do not need to ask the township for permission to build.

Knowing Princeton's rules is not the same as knowing your lot's eligibility.

Your specific zone, your existing impervious coverage, your setbacks, and your utility constraints all need verification before you commit to an architect. Our $750 Feasibility Study answers the lot-level question in 5 days. The fee rolls 100% into your Permit-Ready Package if you proceed.

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