Alt 1 & Alt 2 Explained, NYC DOB Alterations

by | Last updated Jun 26, 2020 | New York City, NYC DOB

In NYC an Alteration Type 1 or Alt 1 is a building alteration that requires a new Certificate Of Occupancy. An Alteration Type 2 or Alt 2 is a building alteration that does not require a new certificate of occupancy.


Alt 1 or Alt 2

There are different types of fillings with the NYC Department Of Buildings to acquire NYC Building Permits. One very common question we get from clients is “do I need an alt 1 or do I need an alt 2?” Lets see what the difference is between an Alt 1 and an Alt 2. First the DOB loves abbreviations so lets go over a couple.

  • Alt 1 – Alteration Type 1
  • Alt 2 – Alteration Type 2
  • C of O, or CO – Certificate Of Occupancy
  • DOB – New York City Department Of Buildings
  • LNO –  Letter Of No Objection


Alteration Type 1 or Alteration Type 2

The basic difference between an Alteration Type 1 and an Alteration Type 2 is the effect on the Certificate Of Occupancy for the building. If the work you propose will required getting a new or amended Certificate Of occupancy then you must file an Alt 1. Alternatively if the work does not require a new or amended certificate of occupancy you can file an Alt 2.

If you are building a New Building you will File an NB Application.



What is a Certificate Of Occupancy (C of O) (CO)?

NYC Certificate Of Occupancy

The Certificate Of Occupancy is a document that lists the building’s legal use or occupancy. The Department Of Buildings (NYC DOB) issues a Certificate Of Occupancy.

Buildings built before 1938 are not required to have a Certificate Of Occupancy unless they undergo an alteration requiring a new Certificate Of Occupancy.


Alteration Type 1

Changing Certificate Of Occupancy NYC

An Alteration Type 1 or Alt 1 is an alteration resulting in new or amended Certificate of Occupancy. So the entire point of an Alt 1 is to change the C of O or if the building is pre 1938 to get your first C of O. The following changes require an Alt 1 and a new C of O: Change in use, egress, or occupancy.

Changing Certificate of Occupancy NYC

Changing a Certificate of Occupancy in NYC will always require an Alt 1.

Here are some examples:

  • If you have a commercial building or space and you want to convert it to residential.
  • Converting from residential to commercial.
  • If your want to build an addition to your building that changes its use or occupancy.
  • Vertical Enlargements – Adding a floor to a building
  • Increasing the number of apartments in a residential building.
  • Converting a 2 family house into 3 families or more.
  • Change that alters the number of occupants in a space.
  • Building a roof deck in certain cases.

NYC Architect Alteration Type 1

You will need an architect when filing an Alt 1. Make sure to consult with your architect about what type of alteration is right for your project.


Alteration Type 1 to meet New Building Requirements

When you are doing a building addition that increases the square footage by more than 110% you will follow new building regulations but will not file for a new building permit.

That means if the building is 10,000 Square feet and you wish to add 11,000 square feet or more it must be filed as an “Alteration Type 1 to meet new building regulations”. Your building application will be reviewed with the same requirements as a new building.


Alteration Type 1, OT “No Work”

An alt 1 with “No work” is when you are changing the certificate of occupancy or getting a new certificate of occupancy but no actual construction work is being done.


Alteration Type 2 (Alt 2)

An NYC DOB Alteration Type 2 is when you are doing a renovation and not changing the certificate of occupancy. This means no change to the use, egress, or occupancy. Basically this is interior or exterior renovations that leave how the building is used them same. Here are some examples:

NYC DOB Alteration Type 2

NYC Architect Alteration Type 2

You will need an architect when filing an alt 2. Make sure to consult with your architect about what type of alteration is right for your project.


Letter of No Objection

If a building does not have a Certificate Of Occupancy or the Change is in the same use and occupancy group you can apply for a “letter of no objection” (LNO) to make a change in use. If this is approved you can file an alt 2. One example would be converting a store to a restaurant in a building with no Certificate of Occupancy.


Alteration Tye 1 or Alteration Type 2 NYC Filing

DOB protocols are complicated and every situation should be assessed on a case by case basis. In this article we reviewed some of the basics with regards to the difference between and Alt and Alt filing in the NYC DOB. This post does not assume to cover every possible issue or condition, but provide a general overview of the topic.


Thank You for reading our Blog Post on Alt 1 and Alt 2 applications.

Please feel free to post questions or comments below. If you are planning to file an NYC DOB Alteration Type 2 or Type 1 we would be happy to discuss your project. If you are interested in discussing a specific project please contact us directly.


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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 15 years where he has designed renovations and new developments of various building types.