Fire Door Glazing Rules: What the Code Allows

Author: Esteban Galicia

Updated:

Fire door glazing title card illustration

Yes, a fire door can have glass. But the glass must be fire-rated, sized within the limits for the door’s rating, installed in the frame and beads it was tested with, and in most locations it must also meet safety glazing rules. Miss any one of these and the door assembly may fail inspection or fail in a fire.

This guide is for contractors, property managers, architects and owners who need to specify, replace or inspect glazing in fire doors. It uses the model code language as adopted in the US, with New York City examples where they differ. Always confirm the final answer with your local Authority Having Jurisdiction (AHJ).

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TL;DR

  • Glass in a fire door must be fire-rated glazing, listed and labeled for use in a door, and installed in the manner it was tested.
  • Fire-protection-rated glazing is capped at 100 square inches in many door ratings. Larger lites need fire-resistance-rated glazing.
  • Fire rating and safety (impact) rating are separate. A door lite usually needs both.
  • Never cut a lite into an existing fire door in the field. That can void the door’s label.
  • Signs cannot go on the glazing. A missing label is not fixed by a new sticker.

Table of Contents

Why glazing is the weak point of a fire door

A steel fire door is a tested assembly: leaf, core, frame, hinges, latch, seals and, where present, glass. The label on the door covers that assembly as tested. Cut an opening and add glass, and you have changed the assembly.

That is why the rules are strict. Glass behaves differently from steel in a fire. Some products block flames and smoke but let heat through. Others also limit heat transfer. UL’s guide to fire doors and windows classifies fire-protection-rated glazing for doors from 20 minutes (1/3 hour) up to 3 hours, and it notes that factory-prepared doors usually include the glazing frame but not the glass itself. The glass is often bought separately. That makes compatibility your job to verify.

The two kinds of fire-rated glass

The code separates fire glazing into two families. Knowing which one you have decides how big the lite can be.

Type What it does Typical limit in a door
Fire-protection-rated glazing Blocks flame and smoke. Does not stop heat transfer well. Tested under NFPA 252 and similar door tests. Size-limited, often 100 sq in.
Fire-resistance-rated glazing Blocks flame and smoke and limits heat transfer. Tested like a wall assembly. Larger lites allowed where listed.

The New York City Building Code is a clear example. Section 716.5.5.1 says fire-protection-rated glazing over 100 square inches is not permitted in doors, while fire-resistance-rated glazing over 100 square inches is permitted in fire doors.

The UL guide describes the same practice: vision panels beyond 100 square inches should use fire-resistance-rated glazing, evaluated under tests such as NFPA 252, UL 10B or UL 10C. If you want a plain-language refresher on how those test standards and fire ratings relate, this code guide to flame spread and related ratings is a useful companion read.

Glazing rules by door rating

The permitted lite depends on the rating of the door. Here is how it generally works in model-code based jurisdictions. Check your adopted code edition, because local amendments exist.

20-minute doors

These are common for corridor and some residential unit doors. In the model code, the glazing in a 20-minute door must be rated at least 20 minutes, and it is exempt from the hose stream test. That is why some ordinary safety glass shows up in these doors where code allows. Do not assume it. The specific code section and the door manufacturer’s instructions decide.

45-minute, 60-minute and 90-minute doors

These are the doors you see at stairwells, shafts and rated corridors. For 60 and 90 minute doors, fire-protection-rated glass is typically limited to 100 square inches. Using larger vision panels means moving to fire-resistance-rated glass. The NFPA also describes how the fire door rules in NFPA 80 govern the installation, including signage on doors and glazing.

3-hour doors

Doors at the highest rated openings are the most restricted. Industry guidance notes that 180-minute door vision lites are limited, so verify with the door manufacturer and the AHJ before specifying any glass at all. In many designs, the answer is a solid leaf.

Check the label on the glass

Fire-rated glass carries a permanent mark. Under the model code, the marking letters tell you what the glass is approved for. “D” means the glass is permitted in fire door assemblies and meets NFPA 252 fire protection requirements. “H” means it meets hose stream requirements. “T” means it meets the temperature requirements. The marking also states the rating period in minutes.

If you cannot read the mark on a lite, you cannot prove what it is. An inspector will not accept a guess.

Fire rating is not safety rating

This is the most common mix-up we see. A lite in a door has to resist fire. It also has to resist a person hitting it.

Safety glazing is a separate requirement. According to the NFPA 80 inspection checklist for swinging doors, glazing in doors, sidelights and transoms in hazardous locations needs to meet the safety glazing requirements of the local building code, such as IBC Section 2406. Typical triggers include glass within 24 inches of a door, or within 18 inches of the walking surface.

Traditional wire glass is the usual casualty. An NFPA 80 meeting document explains that wire glass in fire doors is now significantly restricted in favor of newer fire-protection-rated and fire-resistance-rated glazing that also meets impact requirements. One more caveat from a code-reference summary on safety glass: a product can be acceptable in a fire opening and still not be safety glazing.

So when you order a lite, ask two questions. What is its fire rating and duration? What is its impact rating for this location?

Fire rating is not safety rating — overview diagram

The whole system must match

Glass alone is not the product. The product is glass, frame (the lite kit), beads, intumescent seals and glazing tape or compound, all tested together.

The UK-based British Woodworking Federation publishes a fact card on fire door glazing for timber doors under UK rules. The regulations differ from US codes, but the principle carries over: the glass, bead, seal and glazing medium must be proven compatible with the specific door by test evidence, and changing one part without that evidence can void certification. A generic fire glass kit that does not match the door manufacturer’s instructions is a classic failure.

In practice, this means:

  1. Get the door manufacturer’s glazing instructions and listing.
  2. Match the glass listing to the door rating and the lite size.
  3. Use the beads, tape and fasteners named in the listing.
  4. Keep the paperwork for the inspector.

Cutting a lite into an existing door

Don’t. The BWF fact card states that field machining an aperture is a major violation that invalidates the manufacturer’s fire rating, even if the glass installed is rated. Apertures should be cut by the original manufacturer or a licensed processor who holds test evidence for that door design.

The same logic holds for labeled steel doors in the US. If a door needs a vision panel, order it prepared at the factory or replace it. For a failed opening that is on a deadline, replacement is often faster than rework. See our fire-rated steel doors for stocked options.

Signs, labels and inspections

Inspectors look at glass and the things stuck to it.

  • Signage. Per the NFPA’s fire door FAQ, signage cannot be installed on any glazing in a fire door and cannot interfere with operation. Keep signs off the glass entirely.
  • Labels. A painted-over or missing label is a leading reason doors fail. The NFPA 80 meeting material above notes that replacing a label takes documentation or an inspection service acceptable to the AHJ. A new sticker is not enough.
  • Damage. Cracked glass, loose beads and gaps around the lite can compromise the assembly. The HUD NSPIRE standard lists glazing damage among the defects that can compromise a labeled door.

Enforcement is tightening around NFPA 80, and the AHJ is responsible for verifying the integrity of the whole assembly, not only the label. Our fire door inspection service in NYC can help you see problems before the inspector does.

Our perspective

Most glazing failures we see are not exotic. They are a lite that was bought separately, a kit that did not match the door, a label painted over during a renovation, or a hole cut in the field to “add a window.” Every one of these is avoidable at the specification stage.

Our perspective — overview diagram

Our advice is simple. Decide early whether the opening needs glass at all. If a solid leaf meets the design and egress needs, a solid leaf is the cheapest and lowest risk choice. If you need vision, write the glass rating, lite size, impact rating and manufacturer listing into the order, and keep the documents with the project file.

We supply fire-rated steel doors, hollow metal frames and commercial hardware, and we offer installation and service. For New York City work, the schedule is often the problem as much as the code. That is why we focus on fast delivery and emergency replacement. Right door, right paperwork, installed once.

— Esteban

Order and install the right opening

If you are replacing a failed door or specifying a new one, we can supply fire-rated steel doors, hollow metal frames and hardware, and handle installation and service. Start with our fire-rated steel doors collection, or browse a stocked option such as the 32 x 84 steel door slab, 90 minute fire-rated. For installation, see our door and frame installation in NYC. Pricing is not published online, so contact us for a quote.

32 x 84 Steel Door Slab, Single Cylindrical Prep – 20 Gauge, Fire-Rated - 90 Min

A short checklist before you buy glass

  1. Confirm the door’s fire rating from its label.
  2. Check the code section for the maximum lite size at that rating.
  3. Decide between fire-protection-rated and fire-resistance-rated glass.
  4. Confirm impact rating for the location, including sidelights and transoms.
  5. Match glass, beads, seals and tape to the door manufacturer’s listing.
  6. Keep the labels visible and the glass free of signs.
  7. Ask the AHJ if anything is unclear.

For a broader view of ratings, see our guide to fire-rated doors: ratings, requirements and how to choose. If a door has already failed, our fire door repair service in NYC covers it.

FAQ

Can fire doors have glass in them?

Yes, if the glass is fire-rated, labeled for door use, and installed in the frame and beads it was tested with. The size is limited by the door’s rating. Larger lites need fire-resistance-rated glazing.

What are the glass requirements for a 20-minute fire door?

The model code requires glazing with at least a 20-minute fire-protection rating, and it is exempt from the hose stream test. Local amendments and the door manufacturer’s listing still apply, so confirm with your AHJ.

Can I add a window to an existing fire door?

Not in the field. Cutting an aperture can void the door’s label, even with rated glass. Have the original manufacturer or a licensed processor do it, or replace the door with a factory-prepared one.

Is fire-rated glass also safety glass?

Not always. Fire rating and impact safety are separate requirements. Check both on the product listing, especially for glass near doors and walking surfaces.

Sources

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