Converting To Multi Family

Converting To Multi Family NYC

(Last Updated On: December 31, 2019)

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 NYC. 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 that 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. You also need to make sure you are okay with the minimum lot sizes for multifamily.

An architect like me can help you with all of this. You can always get a Zoning Analysis on your property to see the development potential. 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.

Building Addition and Conversion to multifamily

Building Addition and Conversion 2 family with addition to multifamily.


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. You can have a top floor mezzanine that does not require an elevator.

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. See another blog post we wrote on the difference between a cellar and basement.


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 in 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 will be required to have handicapped accessibility. ADA or Americans with Disabilities Act is a federal law requiring accessible access.

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

In new buildings or conversions with no elevator requirement, 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 in 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.


Contact Fontan Architecture


Thank You for reading our Blog Post on Converting To Multifamily.

Good Luck with your building conversion. If you would like to speak with an architect, please feel free to Contact Us. You can also 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?

      • Mohammed Rahman

        August 10, 2019 3:14 am

        My house is r3 zone I need to convert to 3 family can I do that ? It’s a brick house legal 2 family. What should I need to do ?

  • 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

  • Andre Lopez

    April 15, 2018 2:30 am

    Hey Jorge,
    I’m considering purchasing a home in Brooklyn, zoned M1-2D. Current sq footage sits at 2380 sq ft. on a lot of 2003 sq ft. I know zoning would allow up to 3400 sq. ft or so. My question is, would it be possible to convert the property to a 3 family, or is the zoning restricted to 1/2 family homes?

    Thank you,

  • David gold

    April 23, 2018 9:48 pm


    When it comes to converting a 4 family to a six family. How does the Dhcr registration work?
    What does it start with?

  • Mike sy

    April 30, 2018 7:18 pm

    I have a two family house in Queens and it’s zones r5 so I would like to convert it into a three family house And the question is, it’s easier to get it done because I wouldn’t need to add any more floor on top of the existing house.the house has a walk in apartment on the first floor (it’s not legal) and one family each on the second and third floor and also there is a basement

  • 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.

  • kevin h

    May 15, 2018 3:55 pm

    what are the chances of converting a 6 unit in Brooklyn to a 4 unit and if it is possible what are the realistic time table to get it done.

  • Zaghir Ahmed

    May 18, 2018 3:39 am

    I’m looking at a 3 story 2 family house. Dept of finance says It’s a 3 family, HPD says it’s 2 families. The building is classified as C0 which I think means 3 families, and there’s no c of o.

    Which is accurate if the two are conflicting?

    Garden unit is its own unit

    The duplex is the parlor and 3rd floor. It is considered one unit even though the parlor level has its own doorway entrance in the building, and other than a stairwell going to the 3rd floor there’s no private doorway to make it a 3rd unit. Does this require a conversion? Or is it possible that it was 3 units at one point?


      • Maria

        June 4, 2019 8:20 am

        Jorge my house is also the same design as Zaghir. I checked the website Zola, it says that the property is located in the R5B zoning. Classified as multi-family, but C of O is actually a 2 family. It has calculated the whole gross area as 2750 but doing the math the 2750 sq feet it’s actually including the basement area. So, is this mean that it is possible to convert to 3family?

  • Jasmine P

    May 18, 2018 10:34 am

    I am so happy that I came across your website and read the information there. It’s very useful for first time home buyers like us. We are about to contract a property in R-5 zoning. Lot area is around 2800 sq ft and building is around 1600 sq ft. FAR as built is 0.58 and it’s a wood frame 2 legal family house. (one bed room apt on each floor; 1Br, Lr, Eik, Full Bath). The house is a little bit small and we are thinking to add an addition to the house and convert into a multi family home but after reading your explanation, we gave up the idea of turning to a multi family home because we cannot demolish the house and built a new one due to the cost. So, now we are thinking to add extra bed rooms on each floor and we would like to ask up to how many bed rooms/bath rooms can we add on each floor if we add an addition to the house in the back because the backyard is really big. Also, can we do a bedroom attic & basement on the new addition also? Would greatly appreciate if you could answer my questions. Many Thanks.

  • Joel M.

    May 26, 2018 6:39 pm

    Hi Jorge, great blog. Question: on a 2 to 3 family conversion, are the sprinklers required inside every apartment, or just the common areas, such as the stairs, hallways, entrance lobby, etc.

  • Maria

    June 26, 2018 12:07 am

    Do you need sprinklers in a two family home in nyc. The house was converted 1941 but was never signed off. We are trying to get it signed off now that we are selling.

  • Jenny

    July 11, 2018 1:37 am

    Could a basement of a 2 family house in queens be connected with the first floor apartment and become legalized. Does this make it a 3 family or just legalizing a basement? Thank you

  • Sam Mubar

    July 12, 2018 10:15 pm

    I’m very confused with fire sprinklers requirements. I have one family house and want to convert my basement into legal apartment and the problem is some architects say is not required if i’m converting from 1 to 2 family and others say yes it’s required in any conversion no matter how many families. Which one is the correct answer?

  • L K

    July 24, 2018 3:06 pm

    Hi, how hard is it to convert a 3 family to a 2 family house? My job does not permit me to obtain a loan for more than a 2 family (weird I know) and I cannot find much information about this process. Thank you.

  • Alan Taveras

    July 26, 2018 2:56 am

    Hi Jorge, I have a 3 family, no CO, built in 1908. HPD I-Card for 3 fam with original plans from 1908 as 3 units so I know I can use it as a 3 fam. It even shows a bedroom in the basement from 1908 LOL. R6 zoning 2,000 sq ft lot. I know the FAR is 2.43 and dwelling unit factor is 680 so I can do almost 5,000 sq ft/680= 7.35 units. Currently, each floor is about 1,300 sq ft plus basement is sizable. Not looking to build on top, looking to cut each floor in half and have 2 apartments per floor since the current set up of 5 bedroom apartments is not really practical. So would like to have a 2bd and 1bd on each floor, plus maybe a studio in the basement (since 1908 plans show a bedroom and all windows are full sized and about 1 foot above ground, hoping it’s not going to be ruled a cellar!) Total would be 7 units. I am currently working with another architect on a different project. He says there is no way to know what is required, how much it will cost, until we actually file proposed plans and receive objections. Not looking to spend a few grand before I even know if it’s doable. Would like to see if you have an idea of what would be required for the conversion (it is a masonry structure, I have fire escape and sprinklers installed already) and approx cost for the required work only (adding 3 kitchens and 3 baths, separate electrical meters, anything else that is required).

  • gary

    July 30, 2018 2:54 am


    Can you convert to a 3 family or more in a R3X zone?

  • Winty Rastogi

    August 15, 2018 4:44 pm

    Hi Jorge!

    We have been looking to buy a single family home in Bayside NYC. For now they fall under R2A zone and are both A2 building class. Do you think they can be converted into 2 family homes as thats what we want to do. Please your advice will be very helpful deciding the house of our dreams.

      • Guanlin Du

        October 23, 2018 6:07 pm

        zr 23-22 if the lot size is big enough r2a zone should be able to convert to 2 families

  • gary

    August 22, 2018 10:05 pm

    my house zone is r3x and r4 what does this mean? can i add more floors to this and add more residential units? it currently has three walk up apartments.

  • david burke

    September 23, 2018 2:28 pm

    Enjoying reading your posts and info.
    Is it feasible to convert a six family into a four family. The units are small and I’d like to build a more substantial unit for me to occupy. Imagine the city of NY does not like to reduction of units and makes it difficult and costly to do. Looking at a number 6 unit buildings in bushwich – which I think woudl be more spacious and manageable for me as a four unit building.

  • Rebecca L

    September 26, 2018 8:33 pm

    Hi Jorge,

    It is my understanding that commercial uses are generally not permitted above residential in the same building. Are you aware of any exceptions to this rule? The building I am looking at is located in a C5-5 District within the Special Lower Manhattan District.

    Thank you for any help you can provide!

  • S

    October 4, 2018 1:22 am

    Hi Jorge – Your article is helpful. Thank you! Do you have any experience converting SRO restricted building (although currently 2 family configuration, without CO) into a Legal 2 family or Legal 3 family? What work / time / money is needed to apply new CO? Thank you.

  • Tom Loo

    October 19, 2018 10:10 am

    I’m considering a 2 to 3 family conversion of a typical 61/2. 6 1/2 and illegal first floor apartment which came that way when this was built in 1970. Where can one find out if the gas and plumbing for this apt is legal? It’s an attached brick building in Queens and some of the adjacent buildings was converted to 3 family in the past ( pre 2014). Would the sprinklers have to be in all rooms or just the stairs and halls? Does the existing bathroom and kitchen have to be removed? Does the existing small bathroom have to reconfigured ie moving walls to be ADA or Just the door be enlarged? Thanks!!

  • Raymond Chau

    November 27, 2018 3:09 am

    Hi Jorge,
    I have have 4 family with RE taxes of $25K. I would like to convert a 4 family into 3 or 2 family. The house zoning is C3 and the area zoning is R2A. There are no no parking space or garage on my property. There are 5 electricity meters and 4 gas meters. I do not want to do too much work other then linking the two apartments together so that I have 2 family in the house. Do I need parking space for the house? How many meters do I have to eliminate?

  • Mark Richards

    January 22, 2019 4:41 pm

    Hi Jorge-

    Great article and something I have been considering doing for a while. I’m curious if there are any tax implications from converting from a 1 family house to a 2 family house. I believe it would still be taxed as Class 1 and so the only increase in taxes should be due to the increased value of the property as a result of the conversion- but it doesn’t hurt to ask.

  • Abdullah

    February 8, 2019 5:12 am

    Hi Jorge,

    I am looking to purchase a property in queens. The CO on DOB site mentions sewer ease access on property, what is that and does effect the value of a house ?

  • Dennis Avitabile

    February 15, 2019 10:26 pm

    Hi Jorge, I own a two-family house in Queens and would like 2 converted two or three family utilizing and legalizing the basement as an apartment. I would like to speak to you regarding this possible project.

  • Rose

    February 23, 2019 7:17 pm


    I own a legal 2 family house but its 3 stories with 3 separate apartments 1 apartment on each floor (it was built that way). Each apartment has 3 bedrooms and a kitchen and their own entrances. The house was built it in 1968 and they called it a mother & daughter. No works needs to be done at all. What would I have to do to convert it to a legal 3 family? Also what if I wanted to make them 3 condos… what be involved in that and would it be extremely expensive in your opinion? My zoning is R5 so multi families and condos are allowed here because I already looked into that. Any information will be highly appreciated… i’m trying to find out how affordable it is to do.


  • Eric A

    March 4, 2019 2:57 pm

    I have a 2-family home in R4 zone. The C of O says there is a basement (on ground floor) for a boiler a boiler room and 1 car garage. The “First” floor is for 1 family and the “Second” Floor is for another family.
    I have 2 questions:
    1) If I want to reconfigure the floors – i.e. create a duplex, use the basement level for living, etc., without changing use (will still be a 2 family home, do I need to file an Alt 1.
    2) If I need to file an Alt 1, do I need to comply with current code for the lot as new construction or can anything be ‘grandfathered’. Current code dictates that the current house is on a lot that is too small for a 2-family house. It also needs a side yard(s), which it currently does not have.

  • Karl K

    March 13, 2019 4:20 pm


    I own a 3-story house with basement in Brooklyn. It is a legal 2-family, and there is an electric meter for the parlor (2nd) floor / 3rd floor duplex and a separate meter for the first floor / basement. My neighbor’s house is identical except that her two meters are for (1) the 3rd floor only and (2) basement/first floor/parlor floor. In other word, my tenant’s apartment is the first floor / basement, but my neighbor’s tenant’s apartment is the 3rd floor only, which I think is a preferable set-up. Can I use my house the same way my neighbor is using her house without filing anything with the city if I am willing to pay the electricity for the entire house?

    Thank you.

  • Marga CC

    March 17, 2019 12:53 am

    My client is looking for a detached house in the Bronx, it’s a legal 2 family house, but set up as 1. Only one meter.
    They told me that the house has an unused FAR of 1000 sqft. Does mean that another floor can be add?

    Thank you in advance.

  • Tiffany L

    March 22, 2019 6:40 am


    When converting a 2 families to a 6 families building, do we need to follow rent stabilization rules? The home was originally built in the 1960’s.

  • Devindra Persaud

    March 27, 2019 2:18 pm

    I have a 4 story 4 family frame building, based on HPD it’s an existing 4 family but the DOB states we cannot use a frame building as a multiple dwelling. Is this correct? can we not convert a frame building to a multiple dwelling? or a 2 family frame to a 4 family frame?

  • Daniel J Pagan

    July 22, 2019 8:08 am

    I’m looking to convert my 1 family home to a 2 family home.

    Staten Island
    Block 511
    Lot 16

    I’m in the process of buying out my mortgage holder so I can renovate and refi w/ a conventional mortgage.

    What is a rough estimate cost to do this?

  • Fahim Anwar

    July 23, 2019 2:31 am

    Hi Jorge, your replies are very useful. I recently had a fire and now in the process with State Farm. FDNY asked DoB for structure check for this 2fam frame house on a C8-1 zone. Currently it has a vacate order by DoB. Should I give preference to an Attorney over Public Adjuster? GC came with FDNY, now awaiting clearance from Ins to work further, I am loosing valuable time, please suggest course of action if possible. Does Alt1 conversion of the house at this time make sense? I would appreciate your thoughts.

  • wilson R portuondo

    January 22, 2020 9:55 pm

    Can you convert a 2 family house into a 3 family house in an R5 Zoning?

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