Adding a Roof Deck to a Townhouse in NYC

by | Last updated Apr 21, 2023 | Renovations, Residential, Townhouses / Brownstones

Can You add a roof deck to a townhouse in NYC?

In order to add a roof deck to a townhouse in NYC you will need to hire an architect to assess the existing conditions, obtain approval from the Department of Buildings, and design all necessary alterations to complete the project. You will need permits from DOB, and LPC in the case of Landmark Townhouses. In some cases you may need to obtain a new Certificate of Occupancy. 

I am Jorge Fontan an architect in New York and owner of Manhattan based architecture firm Fontan Architecture. In this post I will be discussing some of the key issues involved when adding a roof deck to a townhouse.


Adding a Roof Deck

Adding a roof deck is more complicated than most people think. In most cases the easiest part of the project is building the deck. The majority of the money and time that goes into building a rooftop deck in New York city will go to all the other things you need to accommodate the roof deck.

If you are planning to add a roof deck to your townhouse the first thing you should do is call an architect. You discuss the project and fully understand what is involved. As an architect I always try my best to prepare people for what it takes to complete their project.


Structural Analysis for a Roof Deck

The first step to adding a rooftop deck on a townhouse is the structural analysis. We need to assess the existing conditions and determine if the roof structure can support the weight of the pavers and the required live load as specified in the New York city Building code.

When performing a structural assessment we will need to see the roof structure which will be wood joists if you have an old townhouse. If the joists on the roof are not exposed we will have a contractor come and do a few probes. This means making some holes in the ceilings and where the ceiling meets the wall. With these probes we can see the size and spacing of the joist as well as determine the condition. Sometimes we find joists that are sagging, rotten, or pulling out of the masonry wall. These are all issues that need to be addressed.

Once the assessment is complete our team can determine the structural capacity of the roof. If the math works out your roof can support a deck, if not we will need to design a system to reinforce the roof. There is more than one way to add structure to the roof. One option is to completely replace the roof joists. Another way is to sister the roof joists. This means adding a second joist next to each existing joist and bolting them together to make a double joist. The third option is to put a new structure over the existing roof. The existing conditions will greatly impact which route we take.

This project was a full gut renovation with a new room addition on the roof of the Brownstone. The entire roof structure was rebuilt to accommodate the addition of the new room and deck. If you want to learn more about rooftop additions we have another post on Adding an Addition to a Brownstone in NYC.

NYC Brownstone Roof Deck

NYC Brownstone Roof Deck and Stairs


Roof Membrane

If you are going to add a deck on top of your roof membrane you w make it more difficult to replace the membrane in the future. This means maybe now is a good time to do so. The membrane should be evaluated and it ma be time to do new waterproofing on your roof. If you are building a whole new structure you will be doing this anyway.


Adding Guardrails

When you add a roof deck you will need to either have parapets or guardrails that are 42″ above the walking surface. This may mean raising the parapets or installing guard rails. Either way this needs to be worked out as it can be a significant expense in building your roof deck.

Below is a photograph of the guard rails at a roof deck we designed on a Brownstone in Harlem.

Guardrails on Roof Deck in NYC

Guardrails on Townhouse Roof Deck in NYC


DOB Approvals

In New York City your architect will file a structural engineering analysis, plans, and paperwork with the NYC Department of Buildings to obtain approvals and permits for building the rooftop deck. In some cases you may need to obtain a new Certificate of Occupancy. If you are applying for a new C of O this will be a more involved process.


Landmarks Approval

If the townhouse is Landmarked or within a Landmark District you will also need approval from the Landmarks Preservation Commission. If you are adding guardrails or raising parapets your team will build a mock up to be reviewed by LPC. They will want to see what it looks like from the street and how visible it is.

Guardrail Mock Up for Roof Deck

Guardrail Mock Up for Roof Deck


Building a Roof Deck on a Townhouse

The most important thing I want you to know from this blog post is that building a roof deck on a townhouse may sound easy but it can be more complicated than you think. All the ancillary work needed for the roof deck is where the majority of the time, money, and effort goes. Be prepared and work with good quality people. Make sure they are upfront with you and set realistic expectations.

The roof is not the only place to build a deck on a townhouse. You can also build a rear year deck. If you are interested you can look at another post we have on Building a Rear Yard Deck on a Townhouse in NYC. And of course you can always do both if you want to add a roof deck and a rear yard deck.

If you are interested in townhouse renovations and want to read more about townhouses in NYC we have another post on Renovating a Townhouse in NYC which covers a broad range of topics.


Thank You for Reading Our Blog Post on Adding a Roof Deck to a Townhouse in NYC.

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.