Combustible vs Non Combustible Buildings: How to Tell
Is your building fireproof? It sounds like a simple question, but the answer changes which FDNY fire notice you post and the safety advice it gives tenants. Most owners have never checked. Here's how to find out for sure.
The quick answer
In short: Under FDNY rule 3 RCNY Section 401-06, a building is treated as combustible unless its Certificate of Occupancy or Letter of No Objection says it's noncombustible or fireproof, or a registered design professional certifies that in writing.
What the words mean
Noncombustible. Built mostly of concrete, steel and masonry, so fire spreads slowly between apartments.
Combustible. Usually brick walls with wood floors and joists, common in older walk ups and brownstones. Fire and smoke can spread faster.
Brick on the outside doesn't make a building fireproof. Many brick walk ups have wood framing inside, which makes them combustible.
How to tell, step by step
- 1Certificate of OccupancyLook it up on the Department of Buildings site. If it says noncombustible or fireproof, you're set.
- 2Letter of No ObjectionOlder buildings without a C of O may have one that states construction type.
- 3Design professionalAn architect or engineer can certify the construction type in writing.
- 4Nothing on fileThe building is treated as combustible. Use the combustible notice.
Why it matters
Construction type decides which FDNY fire safety notice goes in your lobby and inside every apartment door. It also has to be listed in Part I of your FDNY emergency guide. Using the wrong version gives tenants the wrong advice in an emergency, and it's one of the common sign violations we see.
Tell us your building's construction type and we'll send the right fire safety notices. See fire safety signs
Typical NYC examples
Usually combustible: masonry walls with wood floors.
Often combustible, but check. Some were built fireproof.
Usually noncombustible: concrete and steel.
Check the C of O. Some newer low rise buildings use wood framing.
These are just patterns. Your building's documents decide, not its age or look.
What this looks like in practice
Say the owner of a 1950s six story building assumes it's fireproof because it's brick and has an elevator. The C of O doesn't mention construction type, and there's no Letter of No Objection. Until an engineer certifies otherwise, the building is treated as combustible, so the combustible notice goes up in the lobby and on every door.
Official sources: FDNY 3 RCNY 401-06, FDNY apartment fire safety guide.
Quick answers
How do I know if my NYC building is fireproof?
Check the Certificate of Occupancy or Letter of No Objection. If neither says noncombustible or fireproof, the building is treated as combustible.
Is a brick building fireproof?
Not necessarily. Many brick buildings have wood floors and framing inside, which makes them combustible.
Which fire notice does a combustible building use?
The FDNY combustible (non fireproof) version. See the checklist for every sign.
Not sure what your building needs?
Send us your address and number of apartments. We will tell you exactly which signs to order.
General information based on the NYC HPD Required Signage page as of November 2026. Not legal advice. HPD Signs NYC is not affiliated with the City of New York or HPD. Prices may change. Check nyc.gov/hpd for the latest rules.