NYC DOB Filing Types: Alt-1, Alt-2 & Alt-3 Explained

The Three NYC DOB Alteration Types

When existing NYC buildings undergo work — renovation, structural modification, change of use — the work must be filed with the NYC Department of Buildings as an Alteration. The NYC Building Code (Title 28 of the Administrative Code) defines three alteration types, each with different filing requirements:

Alt-1: Major Alteration (CO Change)

An Alt-1 is required whenever the work changes the Certificate of Occupancy — that is, when the alteration changes the legal use, occupancy group, egress path, or occupancy capacity of the building or any portion of it. Common Alt-1 scenarios include:

• Converting a manufacturing loft (M occupancy) to residential (R-2 occupancy)
• Converting a single-family house to a two-family dwelling
• Adding new floor area to a building (vertical addition)
• Creating new dwelling units within an existing building footprint (NYC's most common loft conversion scenario)

Alt-1 requirements:

• Licensed design professional (Architect or Engineer of Record) must file
• Full set of construction documents required across all affected disciplines
• DOB review path and filing requirements depend on the current scope and DOB rules
• A new or amended Certificate of Occupancy is typically part of project closeout
• All required inspections and sign-offs must be completed before final job closeout

Alt-2: Multiple Trade Alteration

An Alt-2 covers alterations that involve multiple work types but do not change the Certificate of Occupancy. This is the most common filing type for structural work on existing NYC buildings — removing load-bearing walls, modifying the structural system, adding new beams, cutting openings in slabs, or strengthening columns.

Alt-2 applications require:

• Licensed design professional (PE or RA) as the applicant of record for each affected discipline
• DOB NOW: Build submission with the drawings and forms required for the current scope
• For structural work: structural drawings, calculations, and any required special inspection documentation
• DOB review or professional-certification eligibility depends on the current job scope and DOB rules
• Required DOB or special inspections during construction
• Sign-off from the responsible design professional at completion

Alt-3: Minor Single-Trade Alteration

An Alt-3 is limited to minor work involving a single trade that does not affect the CO, life safety systems, or the structural integrity of the building. Examples:

• Boiler replacement (plumbing/mechanical trade)
• HVAC equipment installation on an existing structural roof
• Minor plumbing modifications (changing fixture locations within existing rough-in)

Alt-3 applications typically follow a lighter filing path than Alt-1 or Alt-2 jobs, but teams should still confirm the current DOB requirements for the exact scope. Structural work generally does not fit the Alt-3 pathway. Even modest structural repairs often require a higher filing level with PE-stamped drawings.

Structural Work: Which Filing Type?

For structural alterations to existing NYC buildings, the applicable filing type depends on whether the work changes the CO:

DOB NOW: Build — The Online Filing Portal

NYC DOB alteration applications are generally submitted through DOB NOW: Build. In practice, the filing PE/RA or permit consultant manages that workflow for the owner. Key steps typically include:

1. The filing team confirms the correct applicant account and filing role for the job
2. The filing PE/RA creates the DOB job application with the property address, filing type (Alt-1/2/3), work type, and project description
3. The current drawings and forms required for the filing are uploaded by the permit team
4. The application is submitted electronically and fees are coordinated through the filing workflow
5. Plan examination status is tracked through the DOB NOW dashboard by the filing team
6. Plan examiner objections are answered by uploading revised drawings and written responses
7. Once approved, the permit is issued and the contractor can begin work
8. Required DOB inspections are scheduled through the portal by the appropriate filing party
9. Special inspection reports and engineer sign-offs are uploaded at completion for job sign-off

Plan Examination: Self-Certification vs. Full Review

NYC offers two pathways through plan examination:

• Full DOB Plan Examination: DOB examiners review the submitted drawings and issue objections or comments when revisions are needed. The duration depends on job type, submission quality, and current DOB workload.
• Professional Certification: Some jobs may be eligible for professional-certification pathways, subject to the applicant's authorization status and current DOB rules. Eligibility and risk should be confirmed case by case before choosing that route.

NB Filings: When It's Not an Alteration

For work that qualifies as new construction rather than an alteration under current DOB rules, a New Building (NB) filing is required instead of an Alt filing. NB applications usually involve broader documentation and coordination requirements than alteration filings.