What Is a Mother Daughter House?

We represent buyers across Long Island, Westchester and Connecticut, and it’s the single most common thing people get wrong about a suburban listing. Nicole came to this business from law, and she’s blunt about where that stops: “Most people don’t understand the importance of having a real estate attorney, which is not me. It’s someone who only does real estate deals on a daily basis.” So this is a guide, not advice. It’s also part of what the whole move costs, which is laid out in our guide to the suburbs of NYC.

Is a mother daughter house legal?

The Town of Hempstead’s Building Zone Ordinance defines it. The definition has sat on the books since 24 December 1973, and almost nobody reads it:

Mother-daughter residence. “A one-family home or residence constructed or altered to include a second kitchen for the sole use by the children or parents of the fee resident owner of said one-family home or residence.”

Take it apart, because every clause is doing work:

• “One-family home” means the house stays single-family. It does not become a two-family and is not zoned or taxed as one.
• “Second kitchen” is the legal trigger, not a second bedroom or separate entrance.
• “Sole use by the children or parents” means family only: no tenant, friend or paying lodger.
• “Fee resident owner” means the owner lives there. An investor cannot hold one of these.

In 2009 Hempstead added a sibling version, the immediate family residence, for a brother or sister instead of a parent or child. It carries an extra line that tells you what the rule is defending against: all residents “must live and cook together as a single family, with no roomers, and no bedroom doors that lock from the outside.”

A zoning code with an opinion about door hardware is a zoning code that has met a rooming house.

Mother daughter house Long Island rules start with the second kitchen

Everyone assumes the test is a separate entrance, a meter or whether Grandma has her own front door. The kitchen is the test, and Hempstead defines that too:

Kitchen. “Every space containing a minimum of 60 square feet which is intended, arranged or designed for the preparation or the cooking or warming of food; or containing an integrated cooking, warming and/or food-preparation facility. The term ‘integrated’ shall mean any combination of sink, refrigerator, range or oven.”

Any combination. So a sink, a fridge and something that heats food, in a room the size of a small bedroom. That’s a kitchen. The house now has two of them, and it needs a permit.

Plenty of finished basements cross that line by accident. The wet bar that acquired a microwave, and then a small oven, is in the eyes of the code a kitchen with ambitions.

How a town works out that you have one

This is the part sellers underestimate. Hempstead wrote the detection method into the ordinance in 2003, and it doesn’t need an inspector to come inside.

Each of those is a rebuttable presumption, which is lawyer for: the town doesn’t have to prove it, you have to disprove it. The meters will tell on you before a neighbour does.

The document all of this eventually points back to is the certificate of occupancy, and what it says about the house is what the town will hold you to.

The mother daughter house permit is what you are actually buying

The permit is not part of the house. That sentence costs people money.

Under Hempstead’s ordinance the permit for a second kitchen and separate entrance runs for two years. It stays alive only if updated affidavits are filed before it expires, and no earlier than thirty days ahead. That provision sits in the senior residence section of the code, effective 31 August 1992.

So the questions aren’t “is it legal”. They’re:

• Is there a current permit, and what is its expiry date?
• Who signed the affidavits, and does that person still live there?
• Does the family relationship still qualify after the sale, given that the buyer is not the seller’s child?

That last one catches almost everyone. The permit was granted because a specific parent lived with a specific owner, and you’re neither.

Accessory apartment New York rules change by town

Rules vary by town, and that matters more than any other caveat here. Islip requires the owner to hold at least a 50% interest and live in the main dwelling, with tenants confined to the accessory unit.

Islip’s scheme is a different animal. Its ordinance, added 7 July 1992, allows “small apartments within the existing structure of owner-occupied single-family detached dwellings”. That’s an accessory apartment for a tenant, not a second kitchen for your mother.

Brookhaven runs its own again, and Westchester towns each write their own. The difference between two towns is the difference between a permit and a violation. What the purchase costs on top of that is in our closing cost calculators.

If it turns out not to be permitted

An unpermitted second kitchen turns up in four places, and any one of them can end a deal.

None of that’s exotic. It’s what happens when a house has quietly been doing something for a decade that no document says it may do.

What we see in the field

The listing says mother-daughter with the confidence of a document. It usually isn’t one. The word describes a layout, and the layout is legal or illegal depending on paperwork the listing doesn’t mention. Ask for the permit number in the first email.

Multi-generational buying is rising and the housing stock hasn’t caught up. These setups are in demand on Long Island and in Queens, which is exactly why the ones without permits keep changing hands. If you’re weighing the towns themselves, the richest towns in New York shows where that stock actually sits.

The correction is worth real money at the closing table. A second kitchen without a permit is a defect with a price, and a defect with a price is a negotiation. NestApple buyers receive an average rebate of $22,000 on an average purchase of about $1.1 million, and we’ve returned over $11 million since 2017. Our closing cost calculators cover the rest of what’s due on the day.

Common questions

Is a mother daughter house legal in New York? It’s legal where the town’s zoning permits it and a permit has been issued. Zoning is municipal, so the answer changes at the town line. Hempstead has defined and permitted the use since 1973; other towns write their own rules.

Does a mother daughter house need a separate entrance? No. The trigger in Hempstead’s code is the second kitchen. A separate entrance that isn’t on the approved plans creates its own problem, because the code presumes from it that two families live there.

Can I rent out the second unit? Not under a mother daughter permit. The code restricts the second kitchen to the owner’s parents or children. Renting to a tenant is a different use needing different approval, and it’s the most common way these permits get revoked.

Does the permit transfer when I buy the house? Don’t assume it does. Permits like this are granted on affidavits about who lives there, and both the owner and the family member change when the house sells. Ask the town, in writing, before you sign.

Before you make an offer

If a listing says mother-daughter, ask for the permit. Then ask for its expiry date. Then ask what happens to it when the current owner moves out, and get that answer from the building department rather than from the seller.

It’s a good arrangement and a useful kind of house. It’s also one of the few things in a suburban purchase where the document matters more than the building, and a missing one is worth a serious number rather than a shrug.

We represent buyers across Long Island, Westchester and Connecticut, and hand back up to 2% of the price at closing. See how the buyer rebate works.

Written by Nicole Fishman Benoliel

Co-founder of NestApple and a lawyer admitted to the New York bar, not currently practising.