Back to Resources

    Change of Use & Change of Occupancy

    A plain-English guide to NYC change of use and change of occupancy — what qualifies as a change requiring DOB filings, the ALT-1 process, when a new Certificate of Occupancy is required, and common pitfalls that block conversions from ever getting approved.

    Change of Use: The Definition

    A change of use occurs when a building — or a portion of it — is converted from one use to another. In NYC, this means the new use falls into a different occupancy group from what the current Certificate of Occupancy authorizes. Any change of use triggers a required DOB filing, plan review, and typically a new or amended CO.

    Change of use is one of the most common triggers for ALT-1 permits in NYC. It's also one of the most common triggers for zoning issues, code compliance surprises, and unexpected costs — because a change of use forces the building to meet current code requirements for the new use group, even if the existing structure was grandfathered.

    Planning a conversion? Our zoning analysis and DOB filings services identify feasibility and the filing path before you commit.

    Common Change-of-Use Scenarios

    Commercial → Residential

    Converting a warehouse, factory, or office building into apartments. Historically one of the most common NYC conversions (SoHo lofts, DUMBO, LIC).

    Residential → Commercial

    Converting a ground-floor apartment into retail space. Less common but common in Manhattan and gentrifying neighborhoods.

    Office → Residential

    The current wave — Class B and C office buildings being converted to housing following remote-work vacancy trends and NYC's Office Conversion Accelerator.

    Warehouse → Community Facility

    Converting industrial space to schools, medical offices, or houses of worship. Requires community facility use approvals and often specific zoning.

    Retail → Restaurant

    Adding cooking, ventilation, and seating triggers change of occupancy — even if the retail and restaurant are both in Use Group 6.

    Cellar or Basement Occupancy

    Making previously non-occupiable cellar or basement space into legal occupied space. Always triggers a change of use.

    When a New CO Is Required

    Almost every change of use requires a new (or amended) Certificate of Occupancy. Specifically, a new CO is required when:

    • The new use is in a different occupancy group than the current CO
    • The new use requires different exit paths, fire ratings, or accessibility features
    • The occupant load changes significantly (e.g., converting retail to assembly)
    • The number of dwelling units changes
    • The change alters the building's height or bulk
    • New mechanical or plumbing systems are required for the new use

    The Change of Use Filing Process

    1

    Zoning & Code Feasibility Study

    Before design starts, confirm the new use is permitted in the property's zoning district. Verify the current occupancy group and the target group. Identify any variances, special permits, or CCD1/ZRD1 determinations needed.

    2

    Architectural / Engineering Drawings

    A registered design professional prepares plans showing the existing conditions, proposed changes, egress paths, occupancy loads, fire protection, and code compliance for the new use.

    3

    ALT-1 Filing via DOB NOW

    The PW1 application is filed as an Alteration Type 1 with a change of use / occupancy classification. All required disciplines (structural, MEP, sprinkler, fire alarm) are filed alongside.

    4

    Plan Review & Objections

    DOB examines the plans against current code for the new use. Objections often address egress, fire rating, accessibility, and mechanical compliance — expect multiple rounds.

    5

    Construction & Multi-Agency Sign-Off

    Once permits issue, work proceeds under inspections. FDNY, HPD, DOT, and other agencies must sign off before a CO can be issued.

    6

    New Certificate of Occupancy

    After all sign-offs are complete and the building passes final inspection, DOB issues the new CO reflecting the new use. Operating begins under the new authorization.

    Common Pitfalls to Avoid

    • Buying a building assuming the new use is permitted — before the zoning analysis is complete
    • Underestimating fire rating and egress upgrades required to meet current code
    • Starting work before permits issue — triggers work-without-permit violations and stop-work orders
    • Operating under the new use before the new CO issues — Class 1 violations and vacate order risk
    • Missing zoning constraints on the target use (e.g., manufacturing zones don't allow residential without a variance)
    • Failing to obtain LPC approval when the building is landmarked or in a historic district

    Planning a change of use?

    BVS's zoning analysis and Certificate of Occupancy services identify feasibility, quantify code compliance costs, and shepherd the ALT-1 filing to a new CO. Contact BVS for a free consultation before you close on the property.