Adding a Floor to a Brownstone in NYC

by | Last updated Jul 24, 2023 | Landmarks / Preservation, Townhouses

If you own a townhouse in NYC and consider enlarging it with a new addition, you may ask yourself if this is possible. Many factors will affect the feasibility of an addition to an existing townhouse.


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) to build an addition to a townhouse and the Landmarks Preservation Commission (LPC) if the building is a Landmark or within a Landmark District.

I am Jorge Fontan, an architect in New York and owner of the Manhattan-based architecture firm Fontan Architecture. In this post, I will 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 first thing 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 a landmark. 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 regarding bulk and use. Bulk 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 its height limitation or floor area, building the addition will likely not be possible. Therefore 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 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 say very quickly if the addition is possible, whereas, in others, it may be more complicated.

Brownstone Addition Zoning Analysis

Brownstone Addition Zoning Analysis


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 applying to LPC to enlarge a townhouse, you are subject to one of two types of reviews: staff level or full Commission review and public hearing.
A staff-level review is more straightforward when dealing with LPC, as it will likely be a faster review process. There will be architectural requirements for additions that will dictate what type of review is applicable. For example, the addition’s line of sight and visibility 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 review is our preference 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. The full Commission Review will take longer and be more involved. The biggest problem is that they could raise objections. Of course, there may be ways to work with them by compromising the design to achieve your goals. By this point, you will have spent a great deal of time, energy, and money 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 enlargement from the street, this will be helpful, especially if you are trying to get a staff-level review.

Landmark Brownstone in NYC

Landmark Brownstone in NYC with new addition not visible from the street.


Building a Mockup for LPC Review

LPC will require you to build a mockup before building an addition. A building addition mockup is a temporary structure built to demonstrate the overall size and shape of the enlargement. 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 is straightforward, 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 extent 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 job site 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 our contractor’s mockup 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 historical 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, and construction date, find historical photos, and document the existing conditions.

Historic Research for Brownstone Addition

Historic Research for Brownstone Addition


Rooftop Additions to a Landmark Townhouse

LPC will review a vertical enlargement to a Landmark Townhouse 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, you will 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. It can be reviewed at a staff level if it is only one story and falls within the LPC guidelines. This review type will be ideal if you hope to move the project along and not get caught up in what we affectionately refer to as “Landmarks Hell.”

Below is a picture looking down from the top of the addition. Here we built an addition to the townhouse and a new roof deck. We have another post you can read about Building a Roof Deck on a Townhouse in NYC.

New Manhattan Roof Deck


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 enlargements.

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


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, which will impact your project budget.


Certificate of Occupancy

If you add 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 you pass inspections, the DOB will issue a new C of O for the building.

I mention this because 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 you have the completed home you want when it’s all done.

Townhouse Addition in NYC

Townhouse Addition in NYC


NYC Townhouse Additions

Building an addition to a landmark townhouse in NYC is possible, but this is an involved and complicated process. Logistics and execution of design, architectural character, and many other factors will impact whether this proposal will succeed. I recommend embarking on the project with an open mind. As in any other project, game planning and proper preparation will often determine success.

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


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

I hope this was helpful. If you want to speak with an architect about a potential project, 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.