Alteration Type 1, Alteration Type 2

NYC Alteration Type 1, Type 2 Architect

(Last Updated On: November 20, 2018)

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.


Alteration Type 1 or Alteration Type 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
  • LONO –  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. 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 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 and we wish you the best of luck with your upcoming projects.


New York Architects, Jorge Fontan

Author Jorge Fontan AIA

This post was written by Jorge Fontan, a Registered Architect and owner of Fontan Architecture.


  • 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?

  • Paulette Dacosta

    March 20, 2018 1:06 am

    I have a one family but it is tax as a 2 family I went to dob to try to get some answer was told to apply for a LNO but I got a letter from them saying it’s been disapprove because hpd record indicate a two units and 2stories dof indicate two family dwelling .Do I have file an application ALT-1 what does that entail thank you

  • Immzy C

    March 26, 2018 10:09 pm

    I am buying a house from a seller who did alt 1 and requires C of O but seller is saying they will give me 3 sign offs before closing and will keep some money in escrow. Now my question is if I am buying this house with 3 sign offs then how long it might take to get the actual C of O from the DOB?
    You advise will be greatly appreciated.
    Thank You in advance

  • Richard halls

    April 2, 2018 1:21 pm

    Hi Jorge.
    I would like to build a unattached storage structure , 14 x 22ft in my backyard, does this require a permit.?.

  • L Bysz

    April 12, 2018 11:56 pm

    I bought a one story building in a C2 zone, the certificate of occupancy classification states commercial building and the use states storage. I want to use it as an office do I need to change C of O?

  • Yogi

    April 14, 2018 12:12 am

    Hi Jorge,

    Your post are very informative.
    I have a question for you, I’m in the process of purchasing a property in Queens NY that’s zoned R2 with a 7600SF lot. It is being sold as a single family because there was no CO and DOB gave them a letter to sell as a single family (currently being used as a single family but has a kitchen and full bath on each floor. OASIS and Dept. of Finance have it as 2 family and it’s currently being taxed as a 2 family property.
    Is it possible for me to convert to a 2 family (R2 zoning)? What stepts should i follow? Can the CO be updated since it’s being taxed as a 2 family?
    Thanks in advance.


  • Cynthia

    April 18, 2018 3:36 am


    I own a 2 family house with finished basement built in 1920 so there is no CO on File. Building class is B1 and zoning is c2-2.

    I am thinking of opening a small saltwater fish shop in the basement. I am not changing anything other than adding a wall that divides the basement in half and it will have a door. I’m confused about what i would have to do since i am in a c2-2 zone. Do I need to make any changes? For example, Do I need an architect? Will I need a CO or LNO? Or non at all? Or Can this be classified as a home business? I’m so confused! Please help.

    Thank you!

  • Teddy Deignan

    May 1, 2018 12:07 am

    A pre-1933 (No CO) three story with basement, six unit (two per floor), building was gut renovated. The Alt 2 renovation included enlarging the two ground floor apartments by adding a staircase from each unit to the basement below, effectively doubling the size of each apartment, as well as adding a 1/2 bath in the basement of each unit. Based upon the expansion of the ground floor units into the basement, should this have actually been an Alt 1 project and a new CO required?

  • Kemi Oladipo

    May 3, 2018 8:53 pm

    Good evening,
    I am looking for some clarification. I bought a renovated 3 family property in the bronx 5 years ago, 2 story with a finished basement that has a bedroom. I recently had an HPD inspection where the inspector gave me a violation classifying my “Basement” as a “cellar” and ordered a discontinue use of the bedroom in the basement as well as “FILE PLANS AND APPLICATION AND LEGALIZE THE FOLLOWING ALTERATION OR RESTORE TO THE LEGAL CONDITION EXISTING PRIOR TO THE MAKING OF SAID ALTERATION STUD AND SHEETROCK WALLS ERECTED FROM FLOOR TO CEILING CREATING
    ROOMS THRU-OUT AT CELLAR”. I have no COO because the property is pre-1938 and there is a current LNO on file with the DOB. in addition the Icard on file states the Legal occupancy as 3 apts plus basement. Nothing on the Icard indicates a cellar.

    My question would be how do i go about addressing this? I dont even know what the property was suppose to look like prior to renovations and my purchase of said property. The application on file for when the renovations were done before i purchased was an ALT2.

  • ben sela

    June 7, 2018 2:42 pm

    would adding a restaurant kitchen in a cellar of an existing use group 6 ground floor constitute a change in egress/occupancy. scope also involves adding a stair from ground floor to cellar

  • Chris S

    June 19, 2018 7:50 pm

    I’m looking to purchase a home and the seller has done some work which extended the home only on the 1st floor by approximately 7.5 feet. (Enlarging the kitchen)

    They also added a bathroom to the 1st floor.

    What is the plan of action to make these changes legal and comply with nyc dob rules and regulations.

      • john clagett

        September 18, 2018 1:28 pm

        What liabilities will the owner incur if they choose to not obtain a permit for the completed work? Most importantly, is their home insurance in jeopardy?

  • Jayson

    September 20, 2018 3:20 am

    Hi there. I’m considering an addition to my house – extending first and second floor.

    I looked on DOB Website for NYC and saw about 15 years ago when my neighbor did this they filed Alt 2. They added kitchen and extended second floor bedroom.

    How can I do the same? I wanted to extend kitchen and second fooor bedroom.

    If I add bathroom is that alt 1 or 2?


  • Ian Bock

    October 2, 2018 11:07 pm

    Hi, I’m looking to convert an accessory zoned basement in a Brooklyn group 6 building to a commercial kitchen for a bar in the same building. Can I do this with an alt1? If it makes any difference there aren’t any other occupants of the building (the entire thing will be a bar/restaurant) and it is completely detached from all sourpubdibg buildings. Thanks.

  • Robert Balsamello

    October 8, 2018 11:43 pm

    HI, I am interested in purchasing a property on Staten Island. The lot size is 63 x 85 and the building dimensions are 26 x 27 It is a ranch style home. Would I be able to add a second floor to this building even though the lot is not 100′ deep?

  • Lisa

    October 9, 2018 9:01 pm

    Can both an architect or contractor sign off on an Alt-1?

  • Kathleen Leuba

    October 25, 2018 4:17 pm

    DoB says ALT 2 is needed when moving a load bearing wall. Does that mean I can move a wall that is NOT load bearing ,and skip the step of getting the ALT 2? Studio Apartment: I would like to take down the wall separating kitchen from living room/ and/ take down a closet. Thank you! Kathleen

  • Arsene Remy

    October 26, 2018 7:47 am

    I’m looking to purchase a flip property, a 2 story building classified as a B3 in Bedstuy, no CofO on file. Currently set up a 2 apartments over unfinished basement. My plans are to create a 1st floor and basement owner’s duplex, leaving the second floor as a rental unit. Would this trigger a CofO change or would I be filing an ALT 2 as occupancy will remain the same?

    Your articles are worth more 4 yrs university. Big thank!

  • Jessica smith

    November 5, 2018 10:30 pm

    Hello! We rent an apt in a 2 family dwelling, which the configuration was changed from the duplex being floors 1&2 to the duplex being floors 2&3. The building is pre war (189?). Is our landlord required to have an C of O or an LNO? There is also no record with HPD either… Trying to understand our rights as tenants for an I’ll constructed property.

  • JSH

    November 6, 2018 2:37 am

    So happy to have found your site. I am hoping you can help me. I believe my apartment to be an illegal conversion, which has led to a whole host of issues since moving in five years ago.

    Prior our moving into the unit in 2013, the space had always been commercial space, a fact backed up by a business listing active through 2012, the personal testimony of the 30+ year tenants who live above us, etc. When I search DOB for permits, the permit they used to convert our unit is an A2. They specifically state that in the permits that the use, both existing and proposed, is residential. This despite the fact that it was always commercial space before us—and despite an earlier permit from 2009 that does list the use as commercial (existing and proposed).

    I understand that since the building is pre-1938, it’s possible that the building might have obtained a Letter Of No Objection which allowed for an A2 conversion. However, I cannot find this on the DOB site. Would one be there for me to find? And would they really even be able to obtain one under the facts as I have presented them?

  • Chris

    November 11, 2018 6:52 pm

    Thanks for all the great information! Question on permits. HPD classifies the home as a 3 family and DOF as a 2 family. Been used as a 2 family for a while (2 kitchens). Can the units be combined to a single family or continued to be used as a 2 family but moving one of the kitchens without filing alt-1 and getting a news co? Optimal would be to move and upgrade kitchen. Eliminate some non-load bearing walls. Upgrade mechanicals (including electrical and maybe plumbing). Does the answer change if we add a bathroom or don’t move a kitchen? The heart of the question is how much can be down in a townhouse before an alt_1 is needed, especially when If comes to reducing use from 3 family to 1 or 2 family. Thanks!

  • Nancy E. Murphy

    December 16, 2018 6:17 am

    Wow, not kidding, these exchanges are great! Very interactive feeling.

    We have a 2 family 3 story house currently configured as a duplex down, with an apartment on the 3rd floor. We want to flip and make the garden level the apartment. There is no CofO. There is however an I card showing that there is a bottom duplex and a kitchen on each floor. There is no longer a kitchen on the ground floor. To do what we want, do we need to file an Alt 1? Is the icard always looked at? What if it does not match existing conditons?

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