Alt 1 & Alt 2 Explained, NYC DOB Alterations

by | May 8, 2017 | 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


Alt 1 or Alt 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:

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 Type 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.


[maxbutton id=”1″ ]


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 to speak with an NYC Architect. I hope this article was helpful. We wish you the best of luck with your upcoming projects.


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.

  • Hey Jorge,
    We’re in contract to sell our home in Brooklyn. We’ are faced with the dilemma that the original CO from 1934 states 1 Family and the Dept of Finance states 1 Fam converted to Two Fam. The buyers bank is requesting a LNI. We went to Brooklyn DOB and there’s no file folder found for our Block and Lot , supposedly no Micro either. There’s are Two ALT permits pulled in 1937 attaches to our block and lot file on the website.

    Someone at some point had another electrical meter installed prior to our purchase in 1976.

    What do think our chances are of having a LNO approved ? A No work ALT 1 will take too long to save the sale. We’re considering allotting for a price reduction to reflect the ALT1 no work for a new CO but are scenically that’s might actually kill the deal as well.

    So, what do you think our best course of scrutiny is?


    Stuck in Brooklyn

  • S says:

    Hi Jorge. Thanks for great information!
    I have an Alt 1 in progress. The builders didn’t demo correctly leaving all the wood/floors etc. exposed and now needing replacing. Do we need to amend to a NB to replace all the wood? Thanks.

    • S
      I am not sure I understand the question. But if you have an Alt 1 in progress why don’t you ask your architect. They will be much more familiar with the details of your project than I would be.

  • Andrew Fazio says:

    Hi Jorge,

    I’m currently opening a coffee shop in a building in NYC & currently already have an Alt 2 for food & beverage use. We are having some issues getting an answer regarding whether we can obtain a C of O before we have the final fire alarm inspections done. Are we able to do this at a later date as the proposed timeline to get the inspectors is more than 3 months away and we are ready to open the doors in 4 weeks after we get the certificate of occupancy? Are there any other ways around this as our neighbors who own a pasta shop next door never arranged one and they’ve been open for more than 6 months already.
    Please help

    • You are not going to get a Final Certificate Of Occupancy without complete inspections. You asked if there is a way “around this”. The way is simple: do everything required and follow all the rules. there is no getting around a fire alarm inspection. Do the inspections. Your building needs to be safe.

      • Andrew says:

        Hi Jorge, Thanks for the quick reply.
        What I’m ultimately trying to say is that we definitely intend to get the full FA inspection but we were told that it could take up to 3 months before they could come out and inspect our place. We are almost ready to open the doors in roughly 4 weeks time. Is there a way to fast track this situation is what I was trying to say in my previous post?

  • Hello my name is Loena,
    Just bought a business a bar restaurant and I’m having trouble applying for the liquor license because the building which is an old building had a LNO of 2010 and they are doing some work in the roof, beside that the sprinkler system got renovated and still needs to be inspected and signed of.
    As I am the tenant of the first floor and half of the basement once the sprinkler system is signed off will I be able to apply for LNO separately from the building as the roof might take 3-6 months to be done,
    Do I need to file one of the alterations type 1 or 2?
    Plz this will really help

  • Aiko says:

    Hi Jorge,

    We recently bought a two-family house in the Bronx, and are planning to renovate it. We are confused with the whole Alt1 or Alt2 question (although your post did help in clarifying quite a lot – thank you!).

    – The house: No CoO (pre-1938), two-family dwelling. Two floors + finished basement, with the top two floors being used as individual units.

    – The renovation: 1) Combine the top two floors and make into owners’ duplex (-1 unit); 2) Do work on basement to make into legal rental unit (+1 unit). Overall, two units, which is the same as it is now.

    – Use and occupancy will therefore remain unchanged. For the basement, the position of the door and window may change, which we understand could be a change in egress, which, if it is the case, would trigger the need to obtain a new CoO.

    The question is, does the work described above require obtaining a new CoO (hence requiring an Alt1)? Or could we manage the entire renovation under Alt2?

  • Elizabeth Wills-King says:

    Elizabeth here – glad to read your post. My question can I do an extension with adding of 2 bedrooms and a 4 piece bathroom to my B-1 2 Family home. No change from 2 Family just need more space to owners apartment not to Tenant. No C of O building built before 1938. NYC taxes per 2 family. I really want to do the Remodel soon in R 4 zone. Can you tell me if this can be done?

  • michael says:

    Hi Jorge,

    Your website is so helpful and it is very nice of you to provide information to questions. I was wondering if you’d be able to answer a question for me. I am looking to lease some space in a warehouse that is being divided into multiple rental spaces each independent of each other. I am looking to convert the space that i lease into an event space. The property is located in Brooklyn. Assuming the zoning is all ok, who’s responsibility is it to file for the change of use and new C of O. Is it ours or the landlord? And does our filing for our C of O get affected by new tenants that may come into the building and build-out different use spaces? I was told that for my renovations and work i would file an Alt2 and that would be my responsiblilty. I also know that i would have to file for a public assembly license but is it the landlords responsibility to file the Alt 1 and the change of use and new C of O? Will it be possible for me to get my permanent C of O while other tenants are filing and doing their work on their spaces. I guess its more than one question but i’m sure you get the idea.

  • Cherry says:

    Hi Jorge,
    We had purchased property that is one family with office. Zone is R3X. Was told that only 500sqft can be used for office. Can the building be changed to 2 family with office? It’s original CO was for 2 family and R3-2 zone. Thank you for your help

  • Nathalie Wiggins says:

    Hi Jorge

    We would like to change the CofO of a commercial space to be used from an office to an Adult Learning Center. We submitted a letter of no objection to the DOB but it was denied. We now have to file an ALT1. Please advice on how to proceed.

    Thank you

  • David Reins says:

    Good Afternoon, I find this website very informative. I have a circumstance that hopefully you can guide me to start the process. A commercial space was converted to a clinic space, and filed at DOB as an Alt type 2. This new occupancy classification was obviously not identified and one of the required items for this alt 2 sign off is to file an alt type 1 and legalize this new use. Will an ‘Alt Type 1 – No work’ filing -linked to that already permitted alt 2 help me obtain a new COO with this new use?
    Thank You

    • David, I would need more information to answer this question. I would have to review the alt 2 and see if all the work covered by the alt 2 permit satisfies all of the requirements for a change of use.

  • Leave a Reply

    Your email address will not be published.

    Contact Fontan Architecture

    If you would like to speak with an architect you can contact our office and we can discuss your project. Fontan Architecture is a full service architecture firm working on a wide range of project types. Thank you and good luck on your upcoming project. 

    Contact Us