Fire Rated Glazing for Windows and Doors: Everything You Need To Know

Fire rated glazing is an essential component in building planning and design, helping to slow or stop the spread of fire by making glass panels more resistant to flames, smoke and heat.


06 Dec 2022


Simon McAuliffe

In recent years the technological advancements in glazing have produced excellent fire-rated glazing components that comply with the required safety regulations but do not interfere with the architect’s aesthetic vision. Unlike concrete or corrugated steel, fire rated glazing will create bright open spaces, with greater transparency.


In order to successfully specify and supply fire rated glass, a good working knowledge of the performance and design characteristics of today’s offerings is required. This article will explain everything you need to know about fire rated glazing for floors, doors, windows, and walls, laying the foundation to help you choose the right products for your next project.

What is fire rated glazing?

Fire rated glass is a specialist glazing product that has been developed and tested to provide a period of protection during a fire. 

For reference, standard float glass offers very little fire protection (it tends to break at 120°C). Toughened glass or tempered glass lasts slightly longer than float glass – it will withstand heat of up to about 260°C. However, to be fire-rated, glass must be capable of withstanding temperatures in excess of 870°C.

How does fire rated glazing work?

In the event of fire, the glazing will compartmentalise smoke and flames via dedicated spaces between panes of glass, which prevent it from shattering. The heat from the fire will cause the outer layer of the glass to break – however, the broken pane will be held in place by an intumescent layer (a substance that swells as a result of heat exposure).

These layers then rapidly swell to provide insulation – this reduces the level of heat from the fire radiating through into the surrounding rooms and into the protected fire exit routes. Essentially, the extra spaces contain fire-suppressing materials, which both contain the fire, and keep the radiant heat from going into the adjacent room.

This typically works one way, so there is a ‘correct’ and an ‘incorrect’ way to install fire-resistant glass. You also need to be sure you’re using a fire-resistant frame system (including framework, hinges, components, handles etc), for it to be effective.

Is there a difference between fire-protective glazing and fire-resistive glazing?

There are two types of fire rated glazing, which are categorised as fire-protective glazing and fire-resistive glazing. It is vital to know the differences between the two glass materials, as the incorrect specification might jeopardise the safety of building occupants.

Fire-protective glazing is designed to help compartmentalise buildings by defending against the spread of flames and smoke for the amount of time specified (i.e. 30 minutes, 60 minutes, 120 minutes, etc.). It is typically suitable where building codes allow an assembly designated as ‘opening protective’ to enclose a space. It is the less effective version of the two, since it does not protect against radiant heat from fire. Due to this, there is a limit to the amount of ‘fire protective’ material that you can use in a certain space for most building codes.

Fire-resistive glazing has no such limitation; instead, it adds further protection by blocking the transfer of radiant and conductive heat.  It is tested to the stringent fire-resistance test standards for walls (including ASTM E119 and UL 263), and can therefore exceed 25 percent of the total wall area. It is typically suitable where building codes require an assembly designated ‘fire resistant’ to enclose a space and it is essential for glass floors, because if they weren’t insulated from the heat they would become too hot to walk on.

What is the fire rating system?

Fire rated glass is classified by the amount of time it provides for integrity and insulation, and is broken down into numbers for UK building regulations. These numbers are the measure in minutes that the system can withstand in that category before breaking down.

The first number is structural integrity, which is how long the glass will remain in situ in its frame/fixings under the effects of fire, which is crucial for any load-bearing walls or other structures. This also denotes the glass’s ability to prevent the passage of flames and hot gas through the glass when exposed to fire on one side. 

The next number measures the heat resistance or insulation of the glass i.e. the amount of time the glass will act as an effective barrier against flames, heat and smoke under the effects of fire. When tested, the glazing must limit the temperature on the non-fire side of the glazing to no more than an average of 140C and no more than 180 C in any single position.

All these measurements range from 20 minutes to 3 hours, with most being an average of 45 minutes. This is enough time for most residential and low-risk areas since it is enough time to evacuate a smaller building.

The above categories are also split into the duration of protection the glass provides for Integrity and Insulation. These fire protective levels are broken down into E classifications to denote its performance.

E = glass with an integrity only rating

El = glass with an integrity and insulation rating

EW = glass with an integrity rating and a degree of heat resistance


What are the uses for fire rated glazing?

The purpose of fire rated glazing is to protect exit ways from a building for a pre-prescribed amount of time to ensure that everyone can escape safely in the event of a fire. These fire-rated glass systems also help to slow down the process of fires spreading throughout the building, thus providing the fire service with more time to attend the fire before it spreads further.

Fire rated glazing is a requirement in certain buildings – usually those with high volumes of footfall, to help slow the spread of fire from one space to another, and to ensure a safe exit route. Every fireproof glass panel is therefore required to act as a barrier to the passage of smoke and/or fire to varying degrees depending on the location of the product and the fire hazards associated with that building.

If you are designing a new build home or renovating an existing property that is over three storeys (this includes loft conversions) then fire rated doors will be required to separate the stairwell and every habitable room located off the stairwell. Fire-rated doors in the home are also required in a two-storey residential property that has a door leading from a garage to the main house.

Fire-rated glass floors offer the absolute highest quality in insulation and protection – even with a fire raging nearby, they can still be walked on with no adverse effects. They can be crucial for maintaining access along fire-escape routes (which often require fire-rated glass floors as standard). For any homeowner or construction professional wishing to include the properties of a glass floor in their plans, to provide daylight into a basement for example,  but also need to meet fire safety regulations, a fire rated walk-on glass floor will be the only answer.

Cinema foyer with cafe seating and large glass facade overlooking Leicester Square

What are the benefits of fire rated glazing?

It almost goes without saying, but fire rated glass will save lives in the event of a fire. It will add precious minutes to allow occupants to evacuate, and help to protect a home or business by giving the fire service extra time to put out the flames.

This type of glazing can be used to ensure that – along with other elements such as walls and doors – fire and smoke does not spread to other parts of a building for a prescribed period. It can be used to provide fire separation or compartmentation as part of an integrated fire safety strategy.

Fully glazed fire doors offer the benefits of fire protection while maintaining light transmittance through areas of a building, resulting in the feeling of a more light and open living space even though they are compartmentalised.

Plus, some fire-rated glass intumescent layers turn opaque in the heat of a fire which stops vision through the glass – this can help to reduce the level of panic when leaving the building.

Can fire rated glazing be insulated?

Most fully glazed fire doors can be double glazed or triple glazed, as required. The need for an insulated solution could be either for acoustic insulation or thermal insulation.

Man drawing an architectural sketch

Fire rated glazing is essential for any architects who are in the early stages of planning a project and need to incorporate health and safety fire regulations into their designs. Using fire-protective and fire-resistive glazing will help to slow or stop the spread of fire, by making glass panels more resistant to flames, smoke and heat.

But fire-resistant glass can only achieve its designed performance when it is part of a complete fire-resistant glazed system. This means that all component parts – such as the glazing seal, beads, fixings and frame material – must be compatible and work together to achieve the required performance, and must be referenced to appropriate and relevant test evidence.

It’s also vital that the fire-resistant glazed system is installed as tested and assessed by a competent authority. The glass must be tested and classified in its proposed end use application, for example as a sky room, sky frame, glass wall, or glass floor or any other glazed system.

Installation must be carried out by properly trained and competent individuals who can demonstrate the necessary knowledge and skills required to satisfy the third party certification schemes.

If you need help with specifying fire rated glazing for your next project, get in touch with us today.