Glass fire resistance: how many minutes do you need?

When specifying glass for fire resistance, you need to decide how many minutes of protection you need.

Typical ratings include:

Thirty minutes for certain fire-resisting doors, partitions and protected escape routes
Sixty minutes for some compartment walls and other fire-resisting elements
Between 90 and 120 minutes in situations requiring longer periods of fire resistance

You need more than just a number, however. The glass may need to provide integrity (E) alone, integrity and insulation (EI), or integrity and radiation control (EW). You'll also need the glazing system as a whole to be fire-resistant – not just the glass.

The precise specification depends on several factors: building type, building location, the function of the glazing and regulatory requirements. In this article, we break down this complex topic into its basics.

Before we go any further, it's important to note that this article isn't intended as a substitute for the building regulations themselves. With that said, we hope it helps you understand the fire-resistant glazing requirements for your project.

Building type

The level of fire resistance required generally increases with the risks associated with the building. For that reason, its use, height, depth and construction can all affect the required rating.

In England, the basic guidance is laid out in Approved Document B, which distinguishes between different types of buildings. These include:

Houses and blocks of flats
Offices
Shops and commercial buildings
Assembly and recreation buildings
Industrial buildings
Storage buildings
Car parks

Different requirements apply to each category. For example, the minimum fire-resistance periods for certain building elements may be higher in a multi-storey office than in a small, single-storey shop.

These requirements can also vary within the same building. A fire door, compartment wall and glazed screen may all need different levels of fire resistance, depending on their location and purpose.

The main thing to note is that fire-rated specifications aren't simple equations (shop = 30 minutes, car park = 120 minutes). They depend on a combination of factors, including the presence or absence of sprinklers.

And while Approved Document B sets out minimum fire-resistance periods for different building elements, these aren't automatically the ratings required for every glazed component.

The importance of height

Height makes a big difference to fire-resistance requirements.

In an office without sprinklers, for instance, the minimum fire-resistance period for certain building elements increases with the height of the top floor. Under Approved Document B for England, an office with a top floor up to five metres above ground level may require 30 minutes. Meanwhile, one with a top floor up to 11 metres may require 60 minutes.

These periods can increase further as the building gets taller.

With sprinklers in place, some of these requirements may be reduced. In the case of very tall buildings, however, 120-minute fire-resistance periods may still be required.

It's important to remember that these are general requirements for building elements, rather than automatic specifications for glazing. The exact rating required for a glazed door, partition or curtain wall depends on its function and the applicable fire safety requirements.

What is the glass doing?

The glass's function is essential to specifying the right fire resistance. "Sixty minutes" alone isn't an adequate description. Instead, you must consider whether the glazing provides integrity only (E), integrity and insulation (EI), or integrity and radiation control (EW).

Here are some common examples:

E30: integrity only for 30 minutes
EI30: integrity and insulation for 30 minutes
E60/EI60: integrity only/integrity and insulation for 60 minutes
E90/EI90: integrity only/integrity and insulation for 90 minutes
E120/EI120: integrity only/integrity and insulation for 120 minutes

EW ratings follow the same principle, adding a requirement to limit radiant heat rather than providing the temperature-rise insulation required for an EI classification.

The precise classification depends on what the glass is doing. Is it part of a vision panel in a fire door, a fire partition, a protected stair enclosure or an external wall?

The glazing's function affects both the number of minutes' fire resistance required and the type of protection it must provide.

Building location

The building's location is also important when specifying fire-resistant glass – in particular, the building's distance from the relevant boundary. This might be a site boundary or a notional boundary between buildings on the same site.

In England, Approved Document B places particular restrictions on external walls within one metre of the relevant boundary. These generally need to provide fire resistance from both sides, and the amount of unprotected glazing permitted is restricted.

If the wall is more than a metre from the boundary, greater areas of unprotected glazing may be permissible. Depending on the circumstances, fire resistance may only need to be demonstrated from inside the building.

However, the rules aren't quite as simple as a one-metre cut-off. The building's use, the area of the external wall and its distance from the boundary all help determine the requirements.

These regulations are intended to limit the spread of fire between buildings, including the risk of heat radiation and flames causing a fire to spread to a neighbouring property.

Regulatory requirements

The UK has no single regulation or document specifying the length of fire resistance required in glazing applications.

Requirements depend on the building's use, height, location and function, and the applicable building regulations differ between England, Scotland, Wales and Northern Ireland.

In England, the main guidance is Approved Document B – Fire Safety, which supports the Building Regulations 2010.

This document covers the spread of fire internally and externally. It contains tables specifying minimum fire-resistance periods for different building elements, organised by factors such as building purpose, height, basement depth and sprinkler provision.

England is also moving away from the older BS 476 fire-resistance testing route. References to these national fire-resistance classifications are scheduled to be removed from Approved Document B from 2 September 2029, subject to transitional arrangements. They will be replaced with references to the European BS EN classification route.

Wales also uses Approved Document B, but its own Welsh edition applies and should be consulted separately. In Scotland, the relevant guidance is found in the Building Standards Technical Handbooks, Section 2: Fire. In Northern Ireland, it's Technical Booklet E: Fire Safety.

Wherever you're specifying glazing, it's essential to check the applicable requirements rather than assuming the same fire-resistance periods apply throughout the UK.

Does fire resistance only apply to glass?

No. You must consider fire resistance across the whole glazing system – not just the glass. This is an essential consideration when specifying glass for fire safety.

The complete assembly needs appropriate evidence of its fire-resistance performance. That includes the glass, frame, beads, seals, gaskets and other relevant components.

Even one unsuitable component can compromise the whole system's fire resistance, potentially leading to non-compliance, project delays, replacements and other headaches.

That's why it's important to specify a complete, appropriately tested glazing system rather than relying on the fire-resistance rating of the glass alone.

What's the maximum number of minutes for fire-resistant glazing?

Fire-resistant glazing systems are available with a range of ratings, including 30, 60, 90 and 120 minutes. Some specialist systems can provide longer periods of fire resistance.

The maximum available rating depends on the system, its configuration and the type of fire-resistance performance required.

The important thing is to specify a system that meets the requirements of the application, rather than simply choosing the highest available rating.

What's the difference between standard glass and fire-rated glass?

Fire-rated glass is specially engineered and tested to provide a specified level of fire resistance. Depending on its classification, it can maintain a barrier against flames and hot gases, limit radiant heat or provide thermal insulation during a fire.

Standard glass doesn't provide the same tested level of fire resistance and shouldn't be used where fire-rated glazing is required.

How Wrightstyle can help

Are you looking for high-quality fire-rated glazing systems for doors, windows, screens and curtain walls? At Wrightstyle, we provide tested steel glazing systems and technical guidance to help you find the right solution for your project.

Get in touch with Wrightstyle today for comprehensive product advice.

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