Adding a Floor to a Brownstone in NYC

by | Last updated Apr 27, 2023 | Landmarks / Preservation, Townhouses / Brownstones

If you own a townhouse in NYC and are considering enlarging it with a new addition, you may be asking yourself if this is even possible. There are many factors that will affect the feasibility of an addition to an existing townhouse, so the question is: Can you add a floor to a townhouse in NYC?

You can add a floor to a townhouse in NYC if the zoning district regulations of the specific property allow for it. You will need approval from the Department of Buildings (DOB) in order to build an addition to a townhouse, as well as the Landmarks Preservation Commission (LPC) if the building is Landmark or within a Landmark District.

I am Jorge Fontan, an architect in New York and owner of Manhattan based architecture firm Fontan Architecture. In this post I am going to discuss some of the basic concepts involved in building an addition to a townhouse in NYC. We will be using one of our projects as an example, where we added on top of a landmark brownstone in Harlem.


Zoning Analysis for a Townhouse Addition

If someone calls me and wants to look into the possibility of building an addition to a townhouse, the absolute first thing that I want to check is the zoning for the property. As an architect, this is even more important to me than whether the townhouse is landmarked or not. If the zoning does not work the project does not work.

The New York City Zoning Resolution determines what you can build on a property as far as bulk and use is concerned. This includes the shape and size of the structure. Zoning will determine height limitations, yard requirements, lot coverage, setbacks, and floor area. For example, if the building is maxed out on it’s height limitation or on its floor area it will not be possible to build the addition. This is why the first step in discussing a townhouse addition is to have an architect review the zoning.

At our office we often provide a zoning analysis to clients as the first step to building a new home or an addition in NYC. Depending on the existing conditions and what zoning district you are in, some of these are much more straightforward than others. In some instances, I will be able to say very quickly if the addition is possible and in others it may be more complicated.


Building an Addition to a Landmark Townhouse

Building an addition to a historic landmark townhouse or one located within a landmark district will require approval from the NYC Landmarks Preservation Commission (LPC). You will also need a permit from the NYC Department of Buildings (DOB) to build any form of addition to a townhouse in NYC. If your townhouse is not a landmark or within a landmark district you can skip the sections of this post on landmarks.

When filing an application for an enlargement of a townhouse with LPC, you are subject to one of two types of reviews: staff level or full Commission review and public hearing.

A staff level review is the preferable option when dealing with LPC, as it will most likely be an easier and faster review process. There are going to be architectural requirements for additions that will dictate what type of review is applicable. For example, line of site and visibility of the addition will need to be established. The overall height of the addition is another matter to take into consideration. If the addition falls within the acceptable limitations, it can be reviewed by LPC staff. This is the easier option as it will take some time but will not be as extensive as a public hearing.

If the addition exceeds the height limitations for a staff level review, the LPC will require a full review by the Commission with a public hearing. This will most certainly take longer and be a much more involved process. The biggest problem is that they could possibly raise objections. Of course, there may be ways to work with them through compromise on the design to achieve your goals. By this point, you will have spent a great deal of time, energy, and money just to receive a potential objection, so be prepared that you may need to rethink the design based on objections raised during the LPC review process.

Below you will see a picture of the front façade of the Brownstone. When this picture was taken the addition on top was complete. If they cannot see the addition from the street this will really be helpful, especially if you are trying to get a staff level review.

Landmark Brownstone in NYC

Landmark Brownstone in NYC with Nonvisible Rooftop Addition


Building a Mockup for LPC Review

In order to build an addition, LPC will require you to first build a mockup. A building addition mockup is a temporary structure built to demonstrate the overall size and shape of the addition. The purpose will be to see how visible the addition is from the street and the magnitude of its impact on the architectural character of the townhouse and block where it resides.

The mockup can be quite simple, usually built of 2 x 4s and orange mesh. The general contractor will assemble this under the direction of an architect, such as myself, and it must accurately represent the proposed extents of the addition design. As the architect for the addition, I must verify its accuracy, document it with sufficient photographs, and invite the LPC staff to come to the jobsite and view the mockup themselves. One warning, sometimes you can wait a while for LPC to come out and see it.

Below is a photograph of the mockup our contractor built for the brownstone addition in Harlem. When the preservationist from LPC came out he walked up and down the streets looking to see if he could see it. Although it was quite a process, they did eventually approve it.

NYC Landmark Addition Mockup example

NYC Landmark Addition Mockup Example


Historic Records

As with any Landmarks project, the process should begin with historic records. As the architect, I need to determine if the building is an individual landmark or within a historic district. We will identify the building style, original architect, construction date, find historic photos, document the existing conditions, etc.


Rooftop Additions to a Landmark Townhouse

A vertical enlargement to a Landmark Townhouse will be reviewed for appropriateness of size, visibility, architectural form, materials, color, and architectural features. The bottom line is that the LPC does not want you to ruin the existing character of the building or neighborhood. You should always have respect for the original architecture for two reasons. First, it will make things easier with LPC. Second, is that you will probably have greater architectural character within the final product if you respect the original design.

Rooftop additions of any significant size will be subject to a public hearing and commission review. If it is only one story and falls within the LPC guidelines, it can be reviewed at staff level. This will be ideal if you are hoping to move the project along and not get caught up in what we affectionately refer to as “Landmarks Hell”.


Rear Yard Addition to a Landmark Townhouse

When proposing a rear yard addition to a landmark structure we need to analyze the block and identify what other properties have existing additions that are not original to the building. This analysis must include the height and depth of the existing additions.

If the rear yard addition is not visible from the street at any point, this will be an advantage in the review process. If the enlargement is visible from the street, you will incur greater scrutiny.


Structural Design

Building an addition to a townhouse will involve structural work. The architecture and engineering team has to assess the existing conditions and determine a proper course of action. Also be aware that old townhouses can have existing problems that need to be fixed and this of course will impact your project budget.


Certificate of Occupancy

If you are adding a floor to your townhouse, you will need a new Certificate of Occupancy. The architect will file an Alteration CO application (formerly known as Alt 1) with the NYC Department of Buildings. After all approvals are issued, the work is complete, all signoff paperwork is submitted, and inspections are passed, the DOB will issue a new C of O for the building.

I mention this because the process for getting a new C of O is quite involved and comes with additional requirements and inspections from DOB. You should always be prepared that this type of work is complicated, time consuming, and costly, but the bright side is that when it’s all done you have the completed home you wanted.


Townhouse Addition in NYC

Townhouse Addition in NYC


NYC Townhouse Additions

It is possible to build an addition to a landmark townhouse in NYC, but this is an involved and complicated process. Logistics and execution of design, architectural character, and many other factors will impact whether or not this proposal will be successful. I greatly recommend embarking on the project with an open mind. As in any other project, game planning in advance and proper preparation will often be the determining factor for success.

If you would like to read more about townhouses in NYC, we have another post on Renovating a Townhouse in NYC that covers a broad range of topics.


Thank You for Reading Our Blog Post on Building an Addition to a Landmark Townhouse.

I hope this was helpful. If you would like to speak with an architect about a potential project, you can contact us at Fontan Architecture directly.


Contact Fontan Architecture


Jorge Fontan
Jorge Fontan

This post was written by Jorge Fontan AIA a Registered Architect and owner of New York City architecture firm Fontan Architecture. Jorge Fontan has earned 3 degrees in the study of architecture including two degrees from the City University of New York and a Masters Degree in Advanced Architectural Design from Columbia University. Jorge has a background in construction and has been practicing architecture for 20 years where he has designed renovations and new developments of various building types.