Converting to multi family from 1 or 2 family

Converting To Multi Family NYC

Many people who own single family and two family homes are interested in converting them to multi family apartment buildings. Any building with three or more residential units is considered multi family. In this post we will explore some of the requirements for converting from a 1 or 2 family house into a multi family building. These regulations are based on New York City Building Codes.


Converting To Multi Family 

The first thing I want to tell you is that this may be more complicated then you think. Lets start with a list of some basic requirements and then we will go into detail on when each is necessary.


  • Zoning
  • Elevator
  • Fire Alarm
  • Fire Sprinklers
  • ADA Accessibility
  • Construction Classification
  • More than 1 Means Of Egress
  • Alteration Type 1 


Zoning Requirements For Converting To Multi Family in NYC

NYC has different zoning districts which determine what you can build. If you own a one or two family home you need to be in a zoning district that allows multi family use in order to convert your home. So the first thing is to verify you are in a multi family residential zoning district. If you are in a commercial zoning district you need to look up the Residential Equivalent Zoning. Once you have determined your zoning district allows for multi family then you need to figure out the density factor. Every zoning district has a formula that determines the maximum allowable number of dwelling units. A dwelling unit is code speak for an apartment. I am not going to go deep into this calculation I recommend you hire an architect.

An architect can help you with this. You can always ask them to do a Zoning Analysis on your property. At our Architecture Firm In NYC we do these types of zoning analysis and building conversions all the time.

Conversion, Addition, or New Building

It may be the case that you have the ability to build an addition to your building. Sometimes it makes sense just to tear down the whole house and start from scratch. But if the structure is appropriate you may look into building an addition. We wrote another post on Building Additions if you want to learn more about that. You have to figure out what makes sense: converting, building an addition, or demolishing and building a new building.


Elevator Requirements for Multi Family Conversions

If you convert to a multi family and you do an addition with a total of 5 stories or more you will need an elevator. All multi family buildings over 4 stories require an elevator. In some instances where the building foot print is very small you may be able to get an elevator waiver. Do not count on an elevator waiver they are not easy to get. I actually spoke with the commissioner of Queens DOB about an elevator waiver in an addition to a building we are doing in Astoria. He put my odds of approval at 50 / 50. I will update and let you know when we get our results. FYI, the property in Astoria was a 2 family we are converting to 5 family and adding 3 stories on top of the existing 2 story house.

If you do have an elevator then every apartment will be required to be ADA / handicapped accessible.

By the way basements count as a story but a cellar does not. Basements are less then 50% underground. A Cellar is more than 50% underground.


Fire Alarm Requirements For Your Building Conversion

If you have 4 stories you will need a fire alarm. I do not believe there are any exceptions to this. Any building over 3 stories requires a fire alarm as per NYC building codes. Fire alarms are not really that expensive relatively speaking.


Fire Sprinklers Required

Do you need fire sprinklers when converting a 1 or 2 family house into multi family.

In New York City fire sprinklers are always required when converting 1 or 2 family homes into 3 or more family, multi family buildings.

I am going to say this again because people always seem skeptical about this when I tell them. YES, you will need to install fire sprinklers. No exception. End of story. I am not going into any detail here. Even after I tell them it’s required people are constantly asking me if they can get away without putting sprinklers – no you can’t. Put fire sprinklers in the building.


Ada Accessibility – Handicapped Accessibility

If you are going from 1 or 2 families to multi family you may be required to have handicapped accessibility. ADA or Americans with Disabilities Act is a federal law requiring accessible access. Here are the instances it is required.

In new buildings or conversions with 4 or more apartments and with an elevator, all apartments must be ADA accessible.

In new buildings or conversions with 4 or more units and no elevator, all units on the first floor must be ADA accessible.

This means if you have an existing first floor above grade (with stairs going up) you may have a problem. In these instances it often makes sense to demo the building or reconfigure the floor elevations. Speak to an architect about your options.


Construction Classification

All buildings fall into a construction classification. You need to figure out if your current construction classification is acceptable for a multi family building. You need proper fire ratings for floors, walls, roof, columns, etc…

If your home is wood framed you will not be able to convert it to multi family. You should demo the house and build a new building. Talk to your architect about the construction classification requirements.


Means Of Egress

Means of egress are exits and stairs. This is linked with construction classification. The number of exits and stairs is a factor of the number of stories, number of apartments per story, number of occupants, and the construction classification. This is a little complicated so you will definitely need an architect to figure this out.


Alteration Type 1

You must file your building conversion as an “Alteration Type 1” with the Department Of Buildings. You must get a new certificate of occupancy after construction in order to legally occupy the building. We have another post on Alteration Type 1 applications if you want to read more.


Converting 2-family into 3-family NYC

It is important to note that when converting 2-family to 3-family you are switching to multi family. Multi family starts at 3 families. A house is 1 or 2 families. Converting from 1 family to 2 family is a bit easier because you do not need to comply with multi family regulations.


Good Luck with your building conversion. 

If you would like to speak with an architect please feel free to Contact Us. Also you can leave a comment or question below.



  • pin lo

    October 10, 2017 1:54 am


    How many car garages are needed in New York City for converting 1 family to 2?

  • Valerie Lashley

    March 8, 2018 11:12 pm

    Thank you for all this information. It was very enlightening. I have a question. If I have a wood frame 2 family house in Bushwick and I want to go up one more story would that be allowed? I don’t want to make it a 3 family home although that was my original idea because after reading this it seems like it’s a lot of trouble.

  • Gianni Vee

    April 6, 2018 2:01 am

    Hey Jorge,

    2,216 square foot house sits on a 3,200 square foot lot in a R3A zoning (Queens, NY). My question is if this house can be converted from a 1-family to a 2-family based on the dimensions I gave you?

    Thank you,
    Gianni V

  • Jordan c

    May 2, 2018 7:20 pm

    Illegal bathroom and kitchen in Property i am interested in purchasing Would like to legalize the work. Will i have to remove everything and start from scratch to do so or is t possible to work with what’s there in an effort not to waste what on its face appears to be good worksmanship

  • Lily

    May 4, 2018 1:28 pm

    What is the average cost of converting from a one family semi attached to a two family semi attached in flushing ny 11355? My property is 50×100 but house is small 25×100. I think house is 1224 sq feet.
    How long would it take to get permission to start the project of converting.
    Many homes in the neighborhood have been converting, so I know my neighborhood is zoned to do this type of conversion.

  • Alex L

    May 10, 2018 4:30 pm

    I have a house that is built three family but the C/O was listed as two family (during ’50s). Old records show “mother/daughter” two apartments/single family and another “2nd” family for the third apartment. There are no alterations that need to happen but the C/O needs to be corrected as per DOB Inspector. What needs to happen next and what are the costs involved?

      • Frank Castelli

        May 18, 2018 4:36 am

        Jorge I have a similar question can you contact me via email.

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