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Ensuring a fire safe and compliant flat roof specification

26 October 2020

When looking to refurbish a flat roof, achieving a specification that helps protect the building from the spread of fire is essential.

Here, Daren Fraser, Head of Technical at Langley Waterproofing Systems Ltd explains the fire regulations and what Facilities Managers should consider before selecting a compliant flat roof system.

The regulations

In England and Wales, Approved Document B (Fire Safety) of the Building Regulations, Section B4, relates to roof coverings; and is concerned with the resistance to the spread of fire from an external source, prevention of the spread of fire to adjacent buildings via thermal radiation, as well as the resistance to flame spread over the roof and/or fire penetration from external sources.

To minimise this risk, Approved Document B outlines boundaries and minimum distances and the required fire resistance of building materials, including roof coverings, based on the distances between buildings.

Testing and classification

Two criteria are used to determine the fire resistance of a roofing material - the penetration of flame and the spread of flame.

The external fire performance of a roofing material is assessed using the European test standard BS EN13501-5.

Under the European standards, which are referenced in Approved Document B, roof systems are classified into five categories based on their performance - Broof, Croof, Droof, Eroof and Froof, with B the highest fire resistant rating.

There are four test processes that each include specific measures designed to meet the legislative requirements of different countries. - t1 for Germany, t2 for Scandinavia, t3 for France and t4 specific to the UK.

The specified test for the UK has two stages designed to meet the stricter obligations demanded by UK regulations, therefore, when selecting a roof system, it is essential to ensure it has passed this test method and therefore has a Broof(t4) classification.

A Broof(t4) classified system is referred to as ‘unrestricted’ or ‘low vulnerability’ and therefore has no minimum distance requirement between adjacent buildings.

Choosing the correct system

For any flat roof system that is proposed, it is important to consider the system build up information to ensure the solution fully complies with the regulations:

Independent certification
Look for a system that has undergone independent testing to verify its performance. For example, British Board of Agrément (BBA) certification or assessment by an independent fire testing organisation will confirm its Broof(t4) classification.

System substitutions
Fire resistance classifications apply to the whole flat roof system, rather than individual components, so any change to the build-up will invalidate the certification.

For example, if the system has been tested and passed with a specific type and thickness of insulation, it cannot be assumed it will perform as expected if the insulation type or thickness is changed.

A leading systems supplier will have ensured their system has been rigorously tested with a range of thicknesses and insulation types to ensure that the required solution is compliant with the Building Regulations.

Tested scenario versus proposed installation
It is also vital to look at the scenario the system was tested in to ensure it represents the building in question.

For example, in all the tests the system may have been installed on a concrete roof deck, which is in effect a best-case scenario.

Therefore, the performance when installed on a combustible material deck cannot be determined. Reputable system suppliers will also have tested their systems in a range of configurations and situations.

Desktop studies
Beware of the use of desktop studies, also known as ‘assessments in lieu of a test’.

This method uses test data to predict how a system will perform, based on similar tests; and minimising this practice was among the key recommendations of the Hackitt Review.

Compliant installation
It’s essential that any roof is installed by a contractor that is trained to do so and in line with the approved specification.

A system supplier will have a database of approved contractors who are certified to install the system.

It is also recommended that you select a supplier that will monitor the work throughout to ensure a correct and fully compliant installation.

To book a detailed CPD presentation on ‘Mitigating Fire in Flat Roofing’ delivered online by Langley’s expert team, visit

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