Can you build an ADU in Union Township? Likely, with conditions.
Yes, with real limits. Union Township permits one interior ADU in owner-occupied single-family homes in the RA and RB zones on lots of at least 5,000 square feet, but detached units, garage conversions, and basement ADUs are not allowed.
What to know about ADUs in Union Township
| Approval | Permitted with conditions. |
|---|---|
| Zones | RA, RB |
| Still applies | Your zone's own setback, height and lot-coverage rules. |
- Interior units only, no detached ADUs, no basement or garage conversions, no accessory structures
- Single-family detached homes only; two-family homes and townhomes are ineligible
- Lot must be at least 5,000 square feet; owner must occupy one of the units
- ADU capped at one-third of the home's net floor area, up to 1,200 square feet
- One additional off-street parking space; the front facade must remain visually unchanged (no visible second entrance)
Union Township allows accessory dwelling units, but its ordinance is built around a specific vision: an apartment carved out inside an existing single-family home, invisible from the street. ADUs are permitted in the RA and RB zones on lots of at least 5,000 square feet, capped at one-third of the home's net floor area up to 1,200 square feet, with owner-occupancy and one additional parking space required. What's not allowed is just as important: no detached backyard units, no basement apartments, no garage conversions, and no second entrance on the front of the house.
If your plan is a backyard cottage, Union Township's current ordinance doesn't support it, that would take a variance. But if your plan is an in-law suite or rental unit within your existing home's footprint (or an addition), the path is real and the 1,200-square-foot ceiling is one of the more generous in the state. The lot-level review determines which side of that line your project falls on and what your specific home supports.
Garden State ADU builds in four Central Jersey counties, and in Union County a partner builder takes jobs like yours in Union Township: see our ADU builder page, in-law suite additions and garage conversions, or get a free zoning check and written estimate.
Common questions about ADUs in Union Township.
Can I build a detached backyard ADU in Union Township?
Not under the current ordinance. Union Township explicitly prohibits ADUs in accessory structures, basements, and garages, the unit must be within the principal dwelling (or an addition to it). A detached unit would require a variance, which is a hearing-based, outcome-uncertain process. If a detached unit is essential to your plan, we can assess your variance odds honestly.
What does qualify in Union Township?
An interior unit in an owner-occupied single-family detached home in the RA or RB zone, on a lot of at least 5,000 square feet. The ADU can occupy up to one-third of the home's net floor area, capped at 1,200 square feet, needs its own parking space, and the house must remain visually a single-family home from the street, no second front entrance.
How big can my Union Township ADU be?
Up to one-third of your home's net floor area, with a hard cap at 1,200 square feet. A 2,400-square-foot house supports up to an 800-square-foot unit. That 1,200-foot ceiling is actually among the more generous in NJ, most towns cap at 750 to 800. We run your home's numbers in the lot-level review.
I own a two-family home. Can I add an ADU?
No. The ordinance limits ADUs to single-family detached dwellings. Two-family homes and townhomes are expressly ineligible. If you're in a two-family, different provisions of the zoning code govern what you can do, and we can walk through those options with you.
Looking for an ADU builder in Union Township?
Here is how we work, plainly. Garden State ADU builds in Central Jersey ourselves: Middlesex, Mercer, Monmouth and Somerset counties. Union Township is outside them, so we connect you with a partner builder in your area. Either way the zoning check comes first: before you hire an architect or sign a construction contract, we read what Union Township's ordinance allows on your specific lot. The check is free.
- 01 · FREECall or form
- 02 · FREEWe check your lot
- 03 · FREESite visit, estimate
- 04 to 07Design, permits, build
Zoning details (for the record)
- Township Code Ch. 30 (Land Use)
- Districts: RA, RB
- Code text last read: July 14, 2026
This is our reading of the ordinance, not legal advice. Codes change. Confirm with Union Township's zoning office before you rely on it.
Knowing Union Township's rules isn't the same as knowing your lot can do it.
Tell us where the house is. We check your zone, your setbacks and your lot coverage against the rules on this page, then connect you with a partner builder in your area. That is free.