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Alt-1, Alt-2, and Alt-3 Filings Explained

For decades, the NYC Department of Buildings categorized all construction work into New Buildings (NB) or Alterations (Alt). Alterations were broken down into three main categories: Alt-1, Alt-2, and Alt-3.

While the DOB is transitioning to a newer filing structure within the DOB NOW system (using categories like "Alteration-CO" and "Alteration"), the Alt-1, 2, and 3 terminology is still universally used by architects, contractors, and real estate professionals. Understanding these categories is essential for navigating NYC real estate.

Why it matters for NYC property owners

The "Alt" type dictates the complexity, cost, and timeline of your project. Crucially, it determines whether you will need a completely new Certificate of Occupancy (CO) when the work is finished. Filing the wrong type of alteration can lead to DOB rejections, severe project delays, and costly architectural redesigns.

The Three Alteration Types

Alt-1 (Major Alterations): These are major changes that affect the building's legal use, egress (exits), or occupancy limits. Examples include converting a commercial building to residential, adding a new story, or changing a two-family home into a three-family home. An Alt-1 always requires the issuance of a new or amended Certificate of Occupancy.
Alt-2 (Standard Alterations): These cover work that does not change the building's use, egress, or occupancy. Examples include typical apartment gut renovations, combining two apartments (without changing the overall building's legal unit count in a way that requires a new CO), or moving non-load-bearing interior walls. Alt-2s do not require a new CO; they are closed with a Letter of Completion.
Alt-3 (Minor Alterations): This category is for minor work that typically involves only one type of trade. Examples include cutting a curb cut, erecting a construction fence, or installing a temporary sidewalk shed.

Check open permits

D.O.B. Guard lets you search your property's history to see if there are old, unresolved Alt-1 or Alt-2 filings that might block a sale.

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What owners or managers should check

If you are buying a building, check the BIS system for open Alt-1 filings. An open Alt-1 means the building does not yet have its new legal Certificate of Occupancy.
Do not attempt to disguise an Alt-1 project as an Alt-2 to save time. The DOB plan examiners will catch the discrepancy, resulting in objections and potential fines.
Ensure your contractor properly signs off Alt-2 jobs to obtain the Letter of Completion. Open Alt-2s are a major red flag during property sales.

How D.O.B. Guard can help

D.O.B. Guard helps you uncover the hidden history of your property. If you discover open legacy Alt filings that are preventing you from refinancing or selling, our network of licensed professionals can help navigate the complex administrative process of closing them out.

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Need help determining your filing requirements or closing an old Alt permit? Request a consultation, or search your building right now.

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Disclaimer: This is general information only. Determining the correct alteration type involves complex zoning and building code analysis. For a property-specific determination on permit requirements, confirm with the relevant NYC agency (e.g., DOB) or consult a licensed architect or engineer. D.O.B. Guard does not provide architectural or engineering advice.

Frequently Asked Questions

Are Alt-1s and Alt-2s still used in DOB NOW?

Technically, no. DOB NOW uses a slightly different naming convention. An Alt-1 is generally equivalent to an "Alteration-CO" (requires a new CO), while an Alt-2 is generally equivalent to an "Alteration" (no new CO required). However, the industry still heavily relies on the legacy terms.

Can I live in the building during an Alt-1?

It depends heavily on the scope of work and building safety plans. In many major Alt-1 projects (like adding a story or a gut conversion), the building must be vacant. Always consult with your architect regarding Tenant Protection Plans and occupancy legality during construction.