Take note: fire-safe façades

Credit: iSock.com/coldsnowstorm

Ensuring fire safety in façade design is critical, yet existing guidance in Approved Document B often requires careful interpretation. To bring much-needed clarity, the Centre for Window and Cladding Technology (CWCT) has recently published two new Technical Notes on the fire performance of façades: TN113 – Fire performance of façades – Introduction; and TN114 – Fire performance of façades – Use of combustible materials.

These are the first two Technical Notes in a series of four that replace previous guidance contained in CWCT TN98. This series is intended to provide those who design and construct façades in the UK with an introduction to the regulations and associated guidance relating to fire performance, and how the regulations can be met in the design and construction of modern façades. They also provide useful information for building designers and fire engineers on fire-related requirements for façades.

We have engaged widely in the preparation of these Technical Notes, including with the Building Safety Regulator in England and the Scottish Building Standards Division, both of which provided feedback on the Notes. This article summarises TN113 and TN114, and previews TN115 and TN116, which are due for publication later this year.

TN113 – Fire performance of façades

This Technical Note provides an introduction to the building regulations relating to fire in England and the associated statutory guidance in Approved Document B. Requirements in other countries of the UK may differ and key differences are described in an annex.

UK Building Regulations require buildings to be designed and constructed to limit the spread of fire:

• Within the building
• Over the external walls of the building
• From one building to another.

They also require provision for warning and escape in case of fire. Satisfying these requirements will affect the design of the façade and TN113 provides an introduction to these requirements.

The Building Regulations give minimum requirements to ensure life safety. These are generally in functional terms, with Approved Documents providing practical guidance that would normally satisfy the functional requirements. Approved Document B (ADB) covers fire.

There are five functional requirements relating to fire performance (B1 to B5), and TN113 summarises these, highlighting the influence they may have on the design and construction of the façade.

It is important to note that the façade cannot be designed in isolation – the design of the façade is affected by decisions about the design of the building. Therefore, a fire strategy needs to be developed by the building designer/fire engineer, with requirements communicated to the façade designer. It should also be noted that the requirements may exceed the recommendations given in ADB to reduce the risk of property damage in fire. These include:

Any requirements for the façade to be fire-resisting

• Identification of compartment walls/floors to allow design of interfaces
• Limitations on reaction to fire of materials that exceed limits in ADB
• Provisions relating to escape routes that affect the façade.

There are also minimum recommendations in ADB that should be met in relation to:

• Provision of cavity barriers
• Limits on the reaction to fire of materials.

TN113 also describes reaction to fire testing, and highlights the importance of ensuring that materials and products are tested in a way that is representative of how they will be used as part of the façade.

Materials and products can be tested in different configurations. It is therefore crucial that those specifying and selecting façade materials understand how products and assemblies have been tested, to ensure that the tested configuration covers the proposed use. A product may give different classifications for different configurations.

TN114 – Use of combustible materials

TN114 provides a detailed interpretation of the various recommendations given in Building Regulations ADB relating to the reaction to fire of materials and products used in the external wall.

In isolation, the different recommendations appear straightforward. However, when considered collectively, and with regulation 7(2), guidance is required to help provide logical conclusions.

While the regulations and guidance discussed in TN114 allow combustible materials to be used in certain situations, it is generally considered that minimising the use of combustible materials in the external wall will lead to the lowest risk of external fire spread.

This simple view does not, however, take account of other performance aspects of the façade, which must also be met, and which may require the use of combustible materials.

As a general rule, where less combustible materials are available without compromising other aspects of performance, it will almost always be appropriate to use them in preference to a more combustible alternative.

Extensive guidance and interpretation in relation to regulation 7(2) and modern façades is already provided by a joint CWCT and CIBSE’s Society of Façade Engineering (SFE) document, updated in 2023. This guidance is freely available (bit.ly/CJCWCTSFEfire) and should be read in conjunction with TN114.

Guidance in TN114

Figure 1: Summary flow chart from TN114

TN114 provides flow charts (see Figure 1) that summarise the recommendations given in ADB regarding combustible materials. These provide a very useful reference, but care is still required. They should be read in conjunction with the specific clauses in ADB, given in the flow charts, for the full context of the recommendations. In relation to ‘external surfaces’, we define what is meant by an external surface and then where the recommendations for external surfaces apply. This sounds straightforward, but when considered with other recommendations, illogical conclusions could be drawn, whereby the recommendations for lower-risk buildings could be more onerous than those for relevant buildings. We provide a pragmatic interpretation that avoids this.

The recommendations for ‘materials and products’ are relatively straightforward; however, there is still some confusion over the definition of a ‘filler material’. This has particular implications for laminated glass, and we explore this issue in the Technical Note.

Two further Technical Notes, TN115 and TN116, are in preparation and there are a number of outstanding issues that we are working hard to address .

Figure 3: Measurement of height for ‘materials and products’ (from Approved Document B)

Conclusion

The fire performance of façades remains a key industry challenge. Our two new Technical Notes provide guidance on the general requirements relating to the façade and then go into detail regarding the use of combustible materials.

Regardless of the interpretations provided, the risk of fire spread because of the specific materials used, and their extent and arrangement, should be considered on a project-by-project basis, to ensure that the functional requirements of the Building Regulations are met.

TN113 and 114 are available from the CWCT website: bit.ly/CJCWCTTNs