Alt 1 & Alt 2

NYC Alteration Type 1, Type 2 Architect

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
  • LONO –  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. 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 issued by the Department Of Buildings that lists the building’s legal use or 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 any alteration that will require a 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.
  • Increasing the number of apartments in a building.
  • Change that alters the number of occupants in a space.
  • Changes in outdoor space can also require an alt 1 like adding outdoor seating in the rear yard of a restaurant.
  • Building a roof deck.

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 are required to follow new building regulations but not required to 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.


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

I hope this article was helpful. If you have any questions please feel free to post a comment or contact us directly. If you are planning to file an NYC DOB Alteration Type 2 or Type 1 we would be happy to discuss your project.



  • Mara

    May 29, 2017 3:07 pm

    This is very helpful. One question I have is, if a building has no C of O but has been a 2-family for most of it’s existence, do you need to file an Alt 1 or an Alt 2 to renovate and change the configuration of apartments. So, to be specific, to change from a double duplex with kitchens on the parlor and 2nd floor, to a triplex over a garden aparment with kitchens on the parlor and garden levels. No change in use or egress. Thanks for any thoughts on this!

  • Dennis Telesford

    June 16, 2017 11:33 pm

    I am trying to obtain some information on how I should proceed with the request from the DOB to file an Alt 1 for a lot which states ‘parking for more than 5 vehicles’; however wants to amend to state 25 vehicles. The DOB is requesting an architect drawing and zoning analysis.

  • Audre

    September 6, 2017 12:29 am

    If I change 2 family house into 1 family and do some extension in the back of the house both floors and extension on the front just the second floor do I need to file alt 1? When I was doing all extensions with out converting into 1 family it was alt 2.
    Also, can I pull permit for alt 1 with dob tracking number or do I need something else ( in Brooklyn)?
    thank you!

      • Audre

        September 6, 2017 11:04 pm

        Jorge, thank you so much for your prompt reply! Appreciate it!

  • Alex

    September 23, 2017 1:19 am

    Jorge, this was very useful!

    To do some work in a townhouse in Manahattan with a current C of O showing 2 apartments and small Com. Facility to convert it to just 3 apartments (moving partitions and maybe some minor plumbing work) Is alteration II fine?


  • Joyce

    October 20, 2017 2:41 am

    I want to open an indoor kids playground/gymnastics in one space with zoning C2-2, group 16. Do I need to change C/O? Which group should I change? How long will it take?

  • Wojciech

    November 8, 2017 9:31 pm


    I have one question regarding this tread, what OT stand for? Thank you

  • ira l cotler

    November 10, 2017 5:32 am

    How do I change a c of o from 1 family to a 2 family

  • RobertH

    November 14, 2017 10:41 pm

    If there have been several CO’s issued to a building, with the different CO’s showing different use groups, is it the most recent CO that governs? For example, if the first CO shows use group 6, and second one shows use group 10, is it a use group 10 only, or a 10 AND 6 for the building?

  • Rich

    November 16, 2017 7:36 pm

    Hello Jorge,

    Your articles are very helpful thank you. We’re in the process of buying a townhouse that was built pre-1938, so there is no C/O and also no LONO. It has always been used as a 2-fam, bottom duplex/top single.

    We’re thinking of making an extension for the bottom 2 floors and leave the top floor as-is. Since it’s an extension would this require us to file for an Alt.1 and new C/O no matter what else?

    Is there any scenario in which we could do an extension with just a LONO and Alt.2, maybe keeping it as a 1-fam?

    Thank you!

  • Christopher Carew

    December 7, 2017 7:41 pm

    I’m planning to convert a raw, one floor, ground floor 12,000 square foot warehouse in Brooklyn, zoned as M1-2, into a food hall. It is a corner space, with a current C of O (from 1963) allowing 45 persons, with a live load of 120. I ultimately plan to keep it mostly raw, with the exception of 20 commercial kitchens (built out by subtenants), and bathrooms, all on the perimeter of the space.

    I know I will need to change the use, and of course the occupancy (thus a Place of Assembly).

    With just the information above, I have 3 questions:
    1.) Do you foresee any issues with doing this?
    2.) What should I expect the landlord to do before taking the space, versus what I should be expected to do? (i.e., Certificate of Occupancy, Place of Assembly)

    Thank you so much for your insight.

  • michelle

    December 11, 2017 7:21 pm

    I have a question we recently rented a commerical space in a pre 1938 building that don’t have CO or LNO on file. the space is reminding open as is, we only painted and upgrade the bathrooms. We’re so confused because some is saying we do and my landlord saying no we don’t

  • Gloria

    March 2, 2018 12:04 pm

    Hi Jorge,
    We are buying a house in queens ny
    Built before 1938 all indicates is a two family? However there is not c of o
    But the attorney says we might have issues in the future with the department of building if we want to sale.
    The house is taxed as a two, has to gas meters, and two electric meters as well.
    Do we need an architect to get the certificate?

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