The New York City Department of Buildings (DOB) utilizes a specific, trigger-based system for classifying construction projects that can be complex for property owners, developers, and tenants. The process is often counterintuitive, as classification is determined not by the physical scope or monetary cost of the work, but by its legal impact on the building itself. This document serves as a strategic rubric for determining the correct permit application type—New Building (NB), Alteration Type 1 (ALT1), Alteration Type 2 (ALT2), or Alteration Type 3 (ALT3)—for a given project. The core principle of the NYC system is that a project's classification is dictated by its effect on the building's legal status. At the heart of this determination is one critical document: the Certificate of Occupancy.

1. The Decisive Factor: The Certificate of Occupancy (C of O)

Strategically, the single most important document in the NYC permit process is the Certificate of Occupancy (C of O), which functions as the building's legal "identity card." The C of O dictates a building's approved use (e.g., residential, commercial), its egress configuration (the number, location, and width of exits), and its occupancy level (the maximum number of people legally allowed in a space). Any project that requires a new or amended Certificate of Occupancy is, by definition, a major alteration that mandates the most rigorous DOB review process, as it signifies a fundamental change to the building's life safety profile.

Strategic Note
The DOB uses the C of O change as a mandatory trigger to force older buildings to upgrade their life safety systems (egress, fire protection) to modern code, mitigating the risks associated with grandfathered, non-conforming conditions.

Therefore, the fundamental question every project owner, architect, and contractor must ask at the outset is, "Will this work require a change to my existing Certificate of Occupancy?" If the answer is yes, the project is automatically classified as an Alteration Type 1 (ALT1), triggering a comprehensive review. The following matrix provides a clear decision-making framework to apply this core principle to your specific project scope.

2. The Permit Determination Matrix

This matrix is the core decision-making tool of this guide. To identify the likely permit type required for your project, find the description in the table below that most closely matches your scope of work. Understanding this classification is the first step in developing a sound filing strategy.

NYC DOB Permit Application Matrix

The triggers for an ALT1 filing are the most consequential for project planning, as they represent a significant increase in regulatory scrutiny. The following section provides a more detailed analysis of these critical thresholds.

3. In-Depth Analysis: The Core Triggers for an Alteration Type 1 (ALT1)

Understanding the specific actions that trigger an ALT1 filing is the most critical strategic step in project planning. Any alteration that affects a building's Use, Egress, or Occupancy (UEO) elevates the project into this high-risk category. This classification mandates a rigorous DOB plan examination that forces the project to demonstrate compliance with modern codes and culminates in a new or amended C of O that legally reflects the building's new risk profile.

3.1 Change in Use

A change in use is a conversion from one major use category to another as defined by the Zoning Resolution (e.g., residential, commercial, manufacturing).

• Examples that trigger an ALT1:

  • Converting a commercial building or space to residential use.

  • Altering a building to increase the number of dwelling units.

3.2 Change in Egress

A change in egress is any substantive modification to the building's means of egress—the path of travel to a public way.

• Examples that trigger an ALT1:

  • Changing the location of exits.

  • Modifying the width of required exit paths.

  • Altering the number of required exits in a building.

3.3 Change in Occupancy

A change in occupancy is any alteration that changes the legal number of people allowed in a space or the building's official occupancy classification under the Building Code.

• Examples that trigger an ALT1:

  • Any change that alters the number of occupants in a space (e.g., densifying an office floor).

  • Establishing a Place of Assembly (PA), defined as an indoor space where 75 or more people congregate for purposes such as entertainment, worship, exercise, education, or civic engagement.

For projects that successfully avoid these C of O triggers, the next step is to distinguish between multi-trade (ALT2) and single-trade (ALT3) filings.

4. Clarifying Minor Work: Differentiating an ALT2 from an ALT3

For the vast majority of renovation projects that do not affect the Certificate of Occupancy, the primary distinction is the number of trades, or work types, involved in the project scope. This factor determines whether an application is filed as an Alteration Type 2 (involving multiple work types) or an Alteration Type 3 (involving only one type of minor work).

Strategic Note: While an ALT3 is simpler for a single task, strategically bundling several minor jobs (e.g., a curb cut and a new fence) under a single ALT2 application can streamline project management and reduce total filing fees. Consult your design professional on the best approach for your scope.

5. NYC's Unique Framework: A National Comparison

A key point of strategic insight for national developers is understanding how NYC's permit framework differs from the model used in most other U.S. jurisdictions. The fundamental difference is one of philosophy:

• The NYC Model is trigger-based, focusing on the legal consequence of the work. The system's primary concern is whether a project will change the Certificate of Occupancy, which is a proxy for the building's legal use and life safety profile.

• The IEBC Model (International Existing Building Code), used in most of the U.S., is scope-based. It classifies alterations by the percentage of the work area being renovated (e.g., Level 1, 2, or 3 Alterations), regardless of the work's impact on legal use.

This distinction has profound strategic implications. For example, a gut renovation of an entire building that does not change its use, egress, or occupancy would be a major Level 3 Alteration under the IEBC, potentially requiring a full building upgrade. In NYC, this same project can often proceed as a more streamlined ALT2 because it does not trigger a change to the C of O. This unique approach allows for extensive physical renovations without invoking the highest level of regulatory scrutiny, a critical advantage for sophisticated developers in the New York market.

6. The Non-Negotiable Role of the Design Professional

For any project requiring a permit, engaging a New York State licensed Professional Engineer (PE) or Registered Architect (RA) is non-negotiable. These professionals are legally responsible for preparing and submitting construction plans and serve two primary functions in the DOB approval process.

• Compliance & Filing: The PE or RA is responsible for preparing construction plans that comply with all applicable NYC Construction Codes and Zoning Resolutions. They are the official applicant of record who submits these documents to the DOB for review and approval.

• Professional Certification: A key strategic option is "professional certification" (or "self-certification"). In this expedited pathway, the licensed PE or RA attests that the filed plans are fully compliant with all applicable laws, bypassing the standard DOB plan examination. This can dramatically reduce the initial DOB review period for a complex ALT1 project from a standard of 3-4 months down to as little as 3-4 weeks.

Ultimately, the licensed design professional is the final authority for determining the correct filing strategy. Their expertise is essential for navigating the complexities of the NYC DOB and ensuring a project moves forward efficiently and in full compliance with the law.

7. Conclusion: A Framework for Strategic Decision-Making

The New York City permit system is governed by a clear, albeit complex, hierarchy. The central principle is that a project's classification is determined not by its size or cost, but by its legal impact on the building’s Certificate of Occupancy. Understanding this framework allows owners and developers to plan projects strategically, anticipating regulatory hurdles and timelines from the earliest stages.

This guide distills the permit hierarchy into a final set of takeaways:

• NB: For entirely new structures resulting in the first C of O.

• ALT1: For any project that changes the C of O via Use, Egress, or Occupancy.

• ALT2: For multi-trade projects that do not change the C of O.

• ALT3: For single-trade minor projects that do not change the C of O.

While this rubric is a powerful preliminary tool for project planning and risk assessment, it is not a substitute for professional counsel. The final determination and filing strategy for any construction project must always be made in consultation with a qualified and licensed NYC Registered Architect or Professional Engineer.