Approved Document B: what it means for glazing and fire safety

How does Approved Document B support fire safety in glazing installations? Find out in our industry guide.



Compliance is a crucial consideration for any building project. It's partly a question of legality – ensuring that your project meets strict industry standards and regulations.

But more than this, it's about making buildings better for people and better for the environment. Increasingly, building specifications focus on making buildings more energy-efficient and better protected against fire and other environmental hazards.

It's no exaggeration to say that dodging compliance simply isn't an option. This is partly because of reputational damage, but overwhelmingly because of the financial penalties that follow non-compliance.

This is true of all aspects of the construction industry – and the world of fire-resistant glazing is no exception.

In the UK, fire safety and glazing are primarily regulated by Approved Document B (Fire Safety) and Approved Document K (Protection from falling, collision and impact).

These documents are both taken from the Building Regulations 2010. They're supported by specific British and European (BS EN) standards that govern performance and installation.

In this article, we explore what Approved Document B means for glazing and fire safety. But before we go any further, it's important to issue a quick disclaimer.

This article is intended purely as a point in the right direction. It's by no means a substitute for the document itself. Always refer to official guidance for accurate and up-to-date information.

What is Approved Document B?

Approved Document B is a statutory guidance document that forms part of the UK's Building Regulations.

It has two parts: "Dwellings" and "Buildings other than dwellings". Both provide builders, architects and developers with practical guidance on how to ensure fire safety in the design and construction of buildings.

The purpose of Approved Document B is to protect people from fire – people including building occupants, firefighters and the occupants of neighbouring properties.

It focuses on four things:

1. Means of escape

Buildings need to be built so that occupants can safely exit in the event of a fire – and so that firefighters can safely access the building.

2. The internal and external spread of fire

Buildings must also be built to limit the spread of flames and smoke between rooms and across the building's exterior.

3. Structural stability and 4. Firefighter access

Finally, buildings must be built so they stay stable long enough for people to exit and for firefighters to enter.

These regulations cover all aspects of construction work. So, how do they apply to glazing specifically?

How does Approved Document B apply to glazing?

Approved Document B stipulates that glazing must restrict the spread of fire between rooms (internal) and between buildings (external).

This means glass must be fire-rated. The regulations mandate minimum ratings. These are typically E30 for integrity or EI30 for integrity and insulation. These minimums are based on the proximity to boundaries and escape routes.

Glazing must be rated according to BS EN 13501-2. Protected stairways, boundary walls and other areas requiring fire resistance need glass with a minimum of E30. Higher safety areas require EI30 to EI120 to prevent the transmission of heat.

If integrity-only (E) glass is used – rather than integrity and insulation (EI) glass – the total area of glass allowed is restricted. These restrictions are set out in Table A4 of Approved Document B.

The restrictions apply to the installation process as well as the materials required. Fire-rated glass must be installed strictly in line with manufacturer guidelines. This often involves intumescent seals – seals that expand in the heat and provide a protective barrier against the fire.

These installation standards are in place to ensure that the fire-rated performance of the glass isn't compromised.

It's important to note, too, that glass is only considered fire-resistant when paired with a suitably rated framing system. The glass and the frame are rated in tandem.

What role does glazing play in fire safety?

Specialised fire-rated glazing plays a critical role in protecting buildings against fire. It does this by acting as a barrier that contains flames, smoke and hot gases while still allowing light to pass through.

It's designed to maintain the compartmentalisation of buildings – in other words, containing a fire to the room where it originated and stopping it from spreading. This, in turn, gives occupants more time to evacuate and the emergency services longer to arrive.



What is fire-rated glass?

Fire-rated glass is a type of glazing designed to contain flames and hot gases in the event of a fire. To be classified as fire-rated, it needs to meet strict standards.

Ordinary annealed glass shatters even at low temperatures. Fire-rated glass, by contrast, can withstand temperatures exceeding 870°C (1,600°F) for a set period. This aids with both evacuation and firefighting.

It works by using multiple layers of glass bonded together with special transparent interlayers, often made from intumescent foam or gel.

When exposed to extreme heat, this interlayer prevents fire from passing through by either:

• foaming up and swelling into a heat-absorbing shield, or
• cooling the glass and holding it in the frame.
  
  

How is glass fire-rated?

Fire-rated glass is rigorously tested and classified according to the time it can hold back fire and the type of protection it offers.

It's measured according to integrity (E) and insulation (EI). E-rated glass acts as a barrier to fire but allows heat to pass through. EI-rated glass, by contrast, prevents the spread of fire and blocks the heat of the fire.

As well as the "E" and "EI" rating, fire-rated glass is given a number. This refers to the number of minutes the glass can safely resist the fire. E30, for example, protects against fire for 30 minutes, while EI90 protects against fire and heat for 90 minutes.

A fire-rated glazing system combines fire-resistant glass, frames, seals and fixings to withstand high temperatures for specified periods.

Wrightstyle is a trusted UK supplier of specialised glazing systems. Our fire-resistant glazing systems are tested to international standards and rated up to EI120. Don't hesitate to get in touch with our experts for industry-leading technical advice.