Adding a Roof Deck to a Townhouse in NYC

by | Last updated Jul 23, 2023 | Renovations, Residential

Can You add a Roof Deck to a Townhouse in NYC?

When adding 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 the Manhattan-based architecture firm Fontan Architecture. In our office, we work on various property types, including Townhouses and Brownstones. In this post, I will discuss some critical issues when adding a roof deck to a townhouse. I will use an example from one of our projects, where we built a new Roof Deck on top of a Landmark Brownstone in Manhattan. We have a post on the Differences Between Brownstones and Townhouses if you are interested.


Adding a Roof Deck

Adding a roof deck is more complicated than most people think. Usually, the easiest part of the project is building the deck. Most of the money and time that goes into making 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 can discuss the project and fully understand what is involved. As an architect, I always try to prepare people for what it takes to complete their projects.


Structural Analysis for a Roof Deck

The first step to adding a rooftop deck to 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 or Brownstone. If the joists on the roof are not exposed, we will have a contractor come and do a few probes. Probing means making holes in the ceilings and where the ceiling meets the walls. With these probes, we can see the size and spacing of the joist as well as determine their condition. Sometimes we find joists that are sagging, rotten, or pulling out of the masonry wall. These are all issues that we need to address.

Once the assessment is complete, our team can determine the roof’s structural capacity. If the math works out, your roof can support a deck. If not, we will then design a system to reinforce the roof. There is more than one way to add structure to the roof. One option is to replace the roof joists completely. Another way is to Sister the Roof Joists. Sistering 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 current conditions will significantly impact which route we take.

In the photo below, you can see one of our projects. We fully gut renovated this Brownstone and built a new addition on top with a roof deck. We rebuilt the entire roof structure to accommodate 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.

Brownstone addition and roof deck

Brownstone Addition and Roof Deck in NYC


Roof Membrane

Adding a deck on top of your roof membrane will make it more difficult to replace the membrane in the future. Therefore maybe now is a good time to do so. The membrane should be evaluated, and it may be time to do new waterproofing on your roof. If you are building a whole new structure, you will do this anyway.


Adding Guardrails

When you add a roof deck, you will need to have parapets or guardrails 42″ above the walking surface. Providing gaurs may mean raising the parapets or installing guard rails. Either way, this must 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.

Townhouse Roof Deck Guardrail

Townhouse Roof Deck Cable Rail Guardrails


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 get a new Certificate of Occupancy. If you apply for a new C of O, this process will be more involved.


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 if it is visible.

Guardrail Mock Up for Roof Deck

Guardrail Mock Up for Roof Deck


Building a Roof Deck on a Townhouse

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 make a rear-year deck. If you are interested, 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.

New Manhattan Roof Deck

New Manhattan Roof Deck


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

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.