Choosing the right fire rated glass for steel doors involves far more than picking a pane that looks the part. The glass, seals, glazing bars and fixings all work together as one tested assembly, and swapping any single component can affect the whole doorset’s certification. This guide answers the questions we hear most often about the glass and components used in fire-rated steel and glass doors, from integrity versus insulating performance through to tinted, obscured and replacement glazing.
Not sure which fire-rated glazing option suits your project? Get in touch with your required classification and we’ll talk you through the options.
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What Glass Is Used in Fire-Rated Steel and Glass Doors?
What Is the Difference Between Integrity and Insulating Fire Glass?
Can Fire-Rated Steel and Glass Doors Have Reeded, Fluted or Obscured Glass?
Can Fire-Rated Steel and Glass Doors Have Tinted or Coloured Glass?
Why Is Fire-Rated Glass Thicker Than Standard Glass?
Do Glazing Bars Affect the Fire Rating of a Steel and Glass Door?
What Seals Are Used in Fire-Rated Steel and Glass Doors?
What Is an Intumescent Seal and How Does It Work in a Fire Door?
Can You Replace the Glass in a Fire-Rated Steel and Glass Door?
Fire-resistant glass isn’t one generic product — the glass used in a fire rated steel and glass door depends on the required fire performance criteria, most commonly expressed as E, EW or EI, and on the specific tested or assessed system the doorset belongs to.
Because these criteria demand different glass constructions, you can’t simply substitute one type of fire-resistant glass for another without checking it against the doorset’s test evidence. As a result, the “correct” glass for your project always comes down to the classification you need and the system your supplier has certified it within.
The terms integrity (E) and insulating (EI) describe two different levels of fire performance, and understanding the difference explains why an E30 doorset and an EI30 doorset can use noticeably different glass.
Integrity-only glass (E) prevents flames and smoke from passing through the door for the rated period, but it can still get extremely hot on the side facing away from the fire. This makes it suitable for applications where people won’t be in close proximity to the unexposed face for extended periods.
Insulating glass (EI), by contrast, also limits how much heat transfers through to the unexposed side. Consequently, EI-rated glass typically uses a thicker, multi-layer construction than E-rated glass of the same time period (for example, EI30 versus E30), because it has to do more work to control heat transfer, not just flame spread.
In short, the letters after the fire rating tell you what the glass actually protects against — not just how long it lasts.
Yes — you can specify reeded, fluted or obscured glazing on a fire-rated steel and glass door, provided it’s compatible with the tested fire-resistant glass beneath it.
Here’s the important distinction. Decorative or obscured glazing is usually applied as an additional layer or film alongside the required fire-resistant glass, rather than replacing it outright. In other words, you’re not choosing between “fire glass” and “reeded glass” — you’re specifying a fire-resistant glass build-up that also achieves the reeded or obscured appearance you want.
Because of this, always confirm decorative glazing requirements with your supplier before manufacture, so they can check the finish against the specific tested system and glazing thicknesses involved.
Tinted and coloured glass options are often achievable on fire-rated steel and glass doors, but availability depends entirely on the system and its supporting test evidence.
Some fire-resistant glass products accept tinted interlayers or applied coatings within their tested configuration; others don’t, because the tint or coating hasn’t been tested as part of that specific build-up. Therefore, rather than assuming any tint is possible, it’s best to treat tinted or coloured glass as a system-specific question from the outset.
If colour or tint forms part of your design brief, raise it early — this gives your supplier time to confirm which tested options genuinely support it, and avoids a late-stage design compromise.
Tall fire-rated steel and glass doors are achievable, but the maximum height of an opening leaf isn’t necessarily the same as the maximum height of the complete glazed assembly.
This distinction is especially relevant for floor-to-ceiling glazed screens.
Where the full structural opening exceeds the permitted door leaf height, a fixed glazed toplight can sit above the door, separated by a horizontal transom. This creates the visual impression of a tall, mostly-glazed screen without requiring the moving leaf itself to span the entire floor-to-ceiling height.
The exact achievable arrangement depends on the system, fire classification, glazing type and overall dimensions involved.
Specifier tip: when planning an unusually tall fire door, provide the full floor-to-ceiling or structural opening height — don’t assume the whole height must be manufactured as a single opening leaf.
Yes — glazing bars in a fire-rated steel and glass door aren’t purely decorative; they can be a functional requirement of the certified system.
Fire-rated glass has maximum tested panel dimensions, so where a design calls for a pane larger than that tested limit, glazing bars, mullions or transoms divide the glazed area into smaller, individually certified sections. This means the position of glazing bars on a fire-rated doorset is often dictated by the tested configuration, not purely by the architectural pattern you’d like to achieve.
That said, many projects successfully combine both goals, using glazing bar layouts that satisfy the tested panel sizes while still delivering the desired look. Sharing your preferred glazing pattern early lets your supplier check it against the panel limits of the chosen system.
Fire-rated steel and glass doors typically use two distinct types of seal, and it helps to know the difference between them.
Intumescent seals sit within the door leaf or frame and expand under heat, closing the gap between the door and frame to maintain fire integrity as the doorset is exposed to fire.
Smoke seals, meanwhile, address cold smoke leakage around the door edges in day-to-day conditions, before a fire reaches the temperature needed to activate an intumescent seal. Not every fire-rated doorset needs smoke seals — it depends on whether the specification includes a smoke-control requirement (often shown as an “S” suffix, such as FD30S).
Because these two seal types do different jobs, a doorset might use one, the other, or a combined intumescent-and-smoke seal, depending on its required classification. For more detail on how intumescent seals work, see the next section.
An intumescent seal is a strip of material fitted into the door leaf or frame that stays inactive under normal conditions but reacts rapidly once exposed to heat.
When a fire reaches a certain temperature, the seal’s chemical composition causes it to expand significantly, often to many times its original thickness. This expansion closes the gap between the door and frame, helping to maintain the fire barrier at exactly the point where flames and hot gases would otherwise escape.
Because this reaction is temperature-triggered rather than mechanical, intumescent seals work automatically and require no action from anyone in the building, which is precisely why they’re such a fundamental (and non-negotiable) component of any certified fire doorset.
| Component | Function |
|---|---|
| E (integrity) glass | Blocks flame and smoke; limited heat protection |
| EI (integrity + insulation) glass | Blocks flame and smoke; also limits heat transfer |
| Intumescent seal | Expands under heat to close door/frame gaps |
| Smoke seal | Blocks cold smoke leakage in normal conditions |
| Glazing bars/transoms | Divide glass into certified panel sizes |
| Decorative/obscured glazing | Applied alongside, not instead of, fire-resistant glass |
Published by Doors of Steel
Specialists in internal steel and glass doors and fire-rated steel door systems.
Last reviewed: September 2026
Every component of a fire-rated steel and glass door — from the glass itself to the seals and glazing bars — has to work as part of one certified system. Speak to our team about your required classification, and we’ll help you specify glass and components that meet it without compromising your design.
ON THIS PAGE
Choose From Topics Below
ON THIS PAGE
Choose From Topics Below
What Glass Is Used in Fire-Rated Steel and Glass Doors?
What Is the Difference Between Integrity and Insulating Fire Glass?
Can Fire-Rated Steel and Glass Doors Have Reeded, Fluted or Obscured Glass?
Can Fire-Rated Steel and Glass Doors Have Tinted or Coloured Glass?
Why Is Fire-Rated Glass Thicker Than Standard Glass?
Do Glazing Bars Affect the Fire Rating of a Steel and Glass Door?
What Seals Are Used in Fire-Rated Steel and Glass Doors?
What Is an Intumescent Seal and How Does It Work in a Fire Door?
Can You Replace the Glass in a Fire-Rated Steel and Glass Door?
Fire-door requirements are project specific. Information within this Knowledge Centre is intended as general guidance and should not replace the project’s fire strategy or advice from the responsible architect, fire engineer, Building Control professional or other competent person.
