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 (architectural, structural, mechanical, plumbing, electrical, sprinkler)
• DOB plan examination — full review by DOB examiners (not self-certification eligible in most cases)
• A new or amended Certificate of Occupancy issued at project closeout
• All required special inspections (Statement of Special Inspections) and sign-offs

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 PE-stamped drawings for each trade
• For structural work: structural drawings, calculations, and a Statement of Special Inspections if triggered by BC Chapter 17
• DOB plan examination (cannot use self-certification for structural Alt-2 in most cases)
• Required DOB or special inspections during construction
• Sign-off from engineer of record 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 do not require plan examination — a licensed contractor pulls the permit and proceeds to work. A DOB inspection may be required at completion. Structural work essentially never qualifies for Alt-3. Even minor structural repairs (repointing a masonry bearing wall, replacing a deteriorated lintel) typically require at minimum an Alt-2 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

All NYC DOB alteration applications are now submitted through DOB NOW: Build at https://a810-bisweb.nyc.gov/bisweb/bsqpm01.jsp. The portal replaced the legacy BIS paper-based system. Key DOB NOW workflow steps:

1. Create an account at DOB NOW: Build and register as a Design Professional
2. Create a new job application — enter the property address, filing type (Alt-1/2/3), work type, and description of work
3. Upload PE-stamped drawings in the required PDF format (max file sizes apply)
4. Submit the application electronically and pay filing fees online
5. Track plan examination status through the DOB NOW dashboard
6. Respond to plan examiner objections (comments) electronically by uploading revised drawings
7. Once approved, permit is issued — contractor can begin work
8. Schedule required DOB inspections through the portal
9. Upload special inspection reports and engineer sign-offs 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 flag objections (code violations, non-compliant details). This process typically takes 4–12 weeks depending on the filing type, submission quality, and DOB workload. Back-and-forth correction cycles are common.
• Self-Certification (Professional Certification): Design professionals with active NYC DOB Professional Certification authorization may self-certify Alt-2 and Alt-3 applications, bypassing standard plan exam review. The PE certifies that the drawings comply with the Building Code. Self-certified applications are subject to random post-approval audits by the DOB. Structural Alt-2 work may be self-certified in some cases but carries significant PE professional liability.

NB Filings: When It's Not an Alteration

For new construction — new buildings, demolition of an existing building and construction of a new one, or additions that exceed 110% of the original building's bulk — a New Building (NB) filing is required rather than an alteration. NB applications have more complex documentation requirements and longer plan examination timelines than Alt filings. The structural engineer's role and drawing requirements are similar for both NB and Alt-1 filings.