R4 Zoning NYC Residential Development

R4 Zoning NYC Building Case Study

We are going to be tracking a small residential development in an NYC R4 Zoning district. This Article will be updated as the project develops. R4 Zoning meaning a Residential 4 Zoning District in New York City. This is a residential building for multiple families.


R4 Zoning NYC

Whats is R4 Zoning?

R4 zoning is a residential zoning district in NYC. It allows all types of residential uses including multifamily residential. R4 buildings are usually small. The maximum building height is 35 feet. The most common building types you see in R4 are attached 1 and 2 family row houses also known as townhouses. These are houses that are attached to each other and share a wall. You are not allowed to build attached houses in an R4 district with more than 2 families in each house. you can also build single or two family detached houses. A detached house is one with yards on all 4 sides that does not touch another house or property line. These are less common in R4 zoning.

You can also develop an R4 lot into a small multifamily apartment building. That is what we are doing. The following is a case study on building 1 small multifamily building in an R4 Zone.[/vc_column_text]

Residential Development Background

Our client owns two adjacent properties on this site. These properties are touching and therefor can be combined. Properties can also be subdivided. The original owner divided one of the 2 properties into 10 lots and built 10 two family houses on them. The houses were roughly 60% finished in construction when the owner went out of business. MY client purchased the properties from the original owner looking to finish the construction. He immediately discover the development was full of problems. The construction and the filing with DOB were a mess. The owner fired everyone involved in the original development and brought in a new team. Our firm came in and helped finish the project. We got everything up to code and finished. We straightened out problems with the DOB and handled inspections.  Eventually we obtained final Certificates Of Occupancy on all 10 of the 2 family homes. The client now has 20 families renting there.

We were now ready to develop the second property. The client wanted to build attached 3 family houses. This is not allowed in R4 zoning. The client did not want to build 2 family attached houses because he would not get as many units as he liked. We proposed to do a small multi family building, and the client agreed. As I mentioned this is not usually the most common development for R4 zoning. Attached 1 and 2 family houses are far more common, but we are going with a multifamily apartment building option.

R4 Zoning Analysis NYC

R4 Zoning Analysis

All developments start with a zoning analysis. The zoning analysis is an in depth look into the zoning regulations affecting the development. The zoning analysis will determine how many apartments we can develop on the site, how many square feet we can build, yard requirements, and all sorts of other details. We are going to keep it to the basics. In this post but there is a great deal of nuance and detail involved in zoning.  That’s why clients often hire us just to do a zoning analysis before starting a project. I recommend you always get your zoning analysis done by a licensed architect.

Development Rights & Floor Area Ratio – FAR

The FAR is a proportion that determines how many square feet you can develop on a property. When we were brought in to complete the development of the first property we realized they had not maximized their allowable square footage. This was fine with us because we can allocate that square footage to the new development. People usually call this “air rights”. Check out an article we wrote discussing NYC Air Rights.

The more technical term for “air rights” is “development rights”. The zoning text uses development rights but either way they mean the same thing. They are the right to develop a property and the amount of square footage you can legally develop on that property as of right.

In our example the first property did not use all of its development rights. We were not about to let that go to waste. So how do you move development rights from one property to another? You combine the zoning lots. This is called a Zoning Lot Merger. Zoning lot is different from a property lot. A zoning lot is the area of property included in determining the zoning for a development. The zoning lot is conceptual. It can be made of multiple property lots as long as the lots are touching. So even though the two properties are separate properties. We can conceptually join them as 1 zoning lot. But they are 2 separate real properties. In reality they are 11 properties but I am trying to keep it simple. The first property was previously divided in 10 real property lots when they did the original houses. Either way we are combining the empty property and the developed properties into 1 zoning lot.

Zoning lot

Determining what you can build on a zoning lot?

When you combine the multiple zoning lots into 1 zoning lot you simply figure out the total allowable square footage of the new combined zoning lot. You then subtract whatever has been used by the completed development of houses. That will give you the new development rights. Are you confused? Lets do some math.

The properties combined lot area is = 28,369.28 Square feet

Therefor the new Zoning lot area is = 28,369.28 Square feet

The FAR in R4 Zoning is .75 that is the ratio to determine the buildable square footage. R4 also has what is called an attic allowance. This allows you to increase the FAR to .9 as long as the increased area is under a pitched roof with a height between 5′ and 8′. We are going to calculate the allowed zoning floor area. This is how much total square footage of floor area is allowed on the zoning lot.

Zoning Floor Area = Zoning lot area X FAR

Zoning Floor Area = 28,369.28 Square feet X .9

Zoning floor area = 25,532.82 square feet

We now have to deduct all the floor area used by the original 10 two family houses. Those all add up to 20,684.3 sq ft.

New Building Floor Area = Allowable Zoning Floor Area – Used Floor Area

New Building Floor Area = 25,532.82 sf – 20,684.3 sf

New Building Floor Area = 4,848.52 sf

So we now know we can build a small building of a maximum 4,848.53 square feet.

The maximum building height in R4 is 35 feet. We aren’t even going to go that high. We are going to do a two story building. Each floor will be about 2,424 sq ft.

How many apartments can we put in the new building?

So we already know our total building floor area. We now need to figure out how many apartments we can put. WARNING This involves more math. The number of units is determined by dividing the Allowable Zoning Floor Area of the Zoning lot by the dwelling unit factor. In R4 zoning the dwelling unit factor is 870. The factor changes between zoning districts. It is only 870 in R3-2, R4, R4-1, and R4B Zoning districts. Do not mix up Zoning Floor Area with Zoning Lot Area when doing this calculation. Here’s the math:

Number Of Dwelling Units = Zoning Floor Area / Dwelling Unit Factor

Number Of Dwelling Units = 25,532.82 sf / 870

Number Of Dwelling Units = 29

That’s 29 counting the original development. We now subtract what has been used by what is allowed. The original development was 10 two family houses. Each family is 1 dwelling unit or 1 apartment. So we are doing 10 x 2 = 20 dwelling units used.

Allowed apartments in new building = Total allowed dwelling units – used dwelling units

Allowed apartments in new building = 29 – 20

Allowed apartments in new building = 9


We can build a maximum of 9 new apartments in a 4,848.52 square foot new building. I told you it was going to be a small building. These are of course the maximums we can build less.


Small Building Design

We are currently designing the new building. We will hopefully be posting a 3D rendering by the end of 2016.

It looks like we are going to end up doing 8 apartments. 4 on each floor of the 2 story building. The client was more interested in doing 8 larger apartments than 9 smaller ones.

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3 thoughts on “R4 Zoning NYC Building Case Study”

  1. So if I purchase a 4000 lot (40×100) detached , I can technically build 4 units @ 870? by using that .90 attic roof (4000*.9/870=4.13?) How do you solve the parking problems per unit? Thanks.

  2. Great article Jorge! I have an R4 lot I’m going to be purchasing in the Bronx. Would love to get your feedback on the best way to maximize the lot.

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