How Can I Legally Add an ADU on Long Island?

Question

"Hey everyone, I’m looking into house hacking in an expensive market and want to explore adding an Accessory Dwelling Unit (ADU) to a property on Long Island, NY. My idea is to buy a 1-4 unit home with an FHA loan, live in one unit, and eventually convert a garage or other space into a legal ADU so I can rent out the main house.

I know Long Island has strict zoning laws, so I’m wondering:

• Which towns or villages allow ADUs? (Specifically looking at garage conversions or detached units.)
• What is the approval process like? Do I need special permits or zoning variances?
• Has anyone applied for the Plus-One ADU Grant? If so, what was the process like?
• Are there any local resources or professionals who specialize in ADU development on Long Island?

I appreciate any insights, personal experiences, or advice from anyone who has gone through this process!"

Matthew Porcaro · Answer

Long Island is slow to the ADU game, but the federal programs like FHA and Fannie Mae are pushing them.

What I'm helping a few clients with on LI right now with is getting houses that are already setup with accessory unit "ready" floorplans.

Which is a lot of LI. Its your split level homes, basement apartments with egress, existing detached structures with liveable units

On LI they call them "non-conforming units" but they're being underwritten now as income producing even by FHA and Fannie Mae/Freddie Mac.

It's definitely a gray area, but the reality is that its "common & customary" to rent out non-conforming (not legally zoned) income producing units in Long Island houses.

Brookhaven and Huntington have beginning to allow them. You will need to submit plans & permits and appear in front of the zoning boards to get them.

Basically what I'm saying is, focus on properties that already have it. Not a new build one.

You can always use a 203k or HomeStyle to fit out the property to become a conforming unit. I wouldn't depend on those grants that have wayyyy to much red tape as mentioned above.

Mohammed Rahman · Answer

Yeah, Long Island’s got strict zoning, but you’ve got options for an ADU. Some towns, like Huntington, Islip, and Brookhaven, have programs that allow accessory apartments, though rules vary. Islip and Brookhaven even offer grants (up to $125K) to help homeowners build or legalize ADUs.

For approval, you’ll need to submit plans, get permits, and maybe go through a public hearing. If your project doesn’t fit zoning laws, you might need a variance, which takes more time.

The Plus-One ADU Program can help with funding, but it has income limits and requires compliance for about 10 years. Groups like the Long Island Housing Partnership (LIHP) and CDCLI can help with the process.

If you’re serious, talk to a local architect or contractor who knows ADU laws in your town. Also, check with the local building department before buying a place to make sure ADUs are allowed.

How Can I Legally Add an ADU on Long Island?

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