What is an Alt CO in NYC

by | Last updated Jun 30, 2023 | NYC DOB, NYC Zoning, Property Development

A Certificate of Occupancy is a document the Department of Buildings issues describing the legal use and Occupancy of a building in New York City. If you are changing a building or home with alterations contradicting the Certificate of Occupancy, you must file an Alt CO application to do so.


What is an Alt CO?

In NYC, an Alt Co or Alteration Certificate of Occupancy is an application type at the Department of Buildings to alter an existing building where there is a change to the Use, Occupancy, or Egress. Alt CO was formerly known as Alt 1. 

Under the new filing system at the NYC DOB, the Alt 1 or Alteration Type 1 application is now an Alt CO, but otherwise, the requirements are the same. Alt CO stands for Alteration Certificate of Occupancy. These applications do not apply to developing a New Building. All new ground-up construction is filed as an NB or New Building application.

I am Jorge Fontan, an architect in New York and owner of Manhattan-based architecture firm Fontan Architecture. In this post, I will review a few examples of what might qualify for an Alt Co application and discuss some of the implications.


When to File an Alt CO?

Most buildings in NYC have a Certificate of Occupancy, although some older buildings built before 1938 might not. The Certificate of Occupancy (C of O) outlines the use and Occupancy of a building along with various other details. We have another post if you want a deeper explanation of the NYC Certificate of Occupancy.

As per the Department of Buildings regulations, an Alt CO is filed to obtain a new C of O when you make any changes to the building’s Use, Occupancy, or Egress. A change in use means a change to the Zoning Use Group. A change in Occupancy means a change in the Building Code Occupancy Group or a change that affects the occupant load for a building.

Here is a list of just a few examples of the types of alterations that qualify for an Alt CO application.

Project Type Examples for an Alt CO

Many more possibilities can trigger an Alteration CO. These were just a few examples.


If You Don’t Have a C of O

The same protocols still apply if the building does not have a Certificate of Occupancy. Any changes in the use, Occupancy, or egress are filed as an Alt CO. At the completion of all requirements; the building will receive a Certificate of Occupancy. 


When You Do Not Need a New C of O

There are many types of alterations that do not require a new Certificate of Occupancy. These are alterations with no change in Use, Occupancy, or Egress. Below are a few examples of projects where you may not need an Alt CO.

Project Type Examples not requiring an Alt CO

  • Adding a bathroom.
  • Adding fire sprinklers
  • Apartment combinations (in most cases).
  • Converting a Store into an Eating and Drinking Establishment (under 75 people)
  • Façade Repairs
  • Interior renovations with no change in use, Occupancy, or egress. 
  • Modernizing your HVAC system.
  • Reconfiguring an office interior.

There are many more possibilities for renovations and alterations that would not require an Alt CO. These were just a few examples. New buildings are filed as an NB application. Alt COs are only filed for existing buildings to remain. 


How To File an Alt CO

An architect files an Alt CO at the Department of Buildings. This application will include a plan exam, paperwork, and filing fees. After completing any associated renovations, the property will be inspected by an NYC DOB inspector before signoff. DOB will issue the new Certificate of Occupancy after signoff.

As an architect in NY, we file many Alt COs in our office. I always explain to my clients the implications of doing so. An Alt CO application can trigger a full review of the property. If you are changing the Occupancy of a building, for example, you may now have ADA Accessibility requirements even if you did not comply in the past. You may need to add fire sprinklers or a fire alarm when changing the use or Occupancy of a building. The process of an Alt CO is more rigorous than a simple renovation may be. There will be many requirements that do not apply to other work types.

Example Architectural Plan from Approved Alt CO

Example Architectural Plan from one of our Approved Alt CO Applications


LNO, Letter of No Objection

If you are trying to make a change where you think you may not need a new Certificate of Occupancy, you can file a Letter of No Objection (LNO) or Letter of Verification (LOV) with the Department of Buildings. The letter of no objection is a simple determination from the DOB where they state if they have no objection to a particular use of a building or space. For example, if you want to use a retail space for eating and drinking under seventy-five people, you can get an LNO approved for this in most cases. 

We have filed many LNOs for different types of projects. If you are interested, we have another post that goes deeper into the subjection of filing a Letter of No Objection with NYC DOB.


Alteration Certificate of Occupancy

If you are renovating a property or planning a change of use that will contradict the existing Certificate of Occupancy. In that case, you must obtain a new C of O. An architect must file an Alt CO application with the NYC DOB, obtain all necessary approvals, complete renovations, and pass inspections before getting a new Certificate of Occupancy.

You will need to hire an architect when altering a building or home in NYC. It is never too early to start these discussions with an architect. 


Thank You for Reading Our Blog Post on The NYC DOB Alt CO.

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.