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Fire Resilience
Standards & Regulations

The importance of product testing and certification in mitigating flat roof fire risk

Lisa Stephens, Product Manager – Building Envelope
Lisa Stephens, Product Manager – Building Envelope
November 28, 2022

A fire outbreak in or near the roof can cause severe damage and disruption to a building and its inhabitants. More than that – it can seriously affect surrounding communities and public services and lead to vast socio-economic losses, as happened after Primark’s Belfast store fire.

The good news is that building engineers and specifiers can take preventative measures to avoid such losses. It starts with having a thorough understanding of roof fire safety requirements and knowing the relevant testing and product certifications to look for.

In this article, Lisa Stephens, Product Manager – Building Envelope, ROCKWOOL UK, explores the building regulations for fire safety in roofs and advises on some of the actions specifiers should take when reviewing and selecting roof insulation products.

But first, why are flat roofs at greater risk of fire?

Although all roofs are vulnerable to a fire spreading from within the building or from falling debris nearby, the accessible surface area of flat roofs makes them a prime candidate for arson. Easy to access, flat roofs can often be the original source of a fire.

Arson is a leading cause of fire, accounting for half of all fire service callouts in the UK, according to reports. Maintenance and refurbishment of flat roofs are among other common causes of fire, while the installation and storage of electrical equipment introduces further hazards.

Solar panels on roofs are also becoming common, which is a benefit for the environment but carries with it additional fire safety challenges. There are known incidences of faults with solar panels caused by ‘arcing’.

Modern uses of the flat roof are opening it up to more fire risks that architects and specifiers need to address during design and construction.

An overview of the Building Regulations for fire safety - Approved Document B (ADB)

The Building Regulations are accompanied by a series of approved documents that provide guidance on how aspects of a building’s construction – such as structure, fire safety, ventilation – can comply with legislation. In England and Wales, the governing body responsible for these documents is the Department for Levelling Up, Housing and Communities[1].

Approved Document B (ADB) provides practical guidance on common building situations about how to meet the requirements of the Building Regulations. It includes many of the provisions needed to protect the lives of building occupants, firefighters and others passing by. Some of the areas it covers are:

  • Means of escape
  • Fire detection and warning systems
  • Fire resistance of structural elements
  • Compartmentation and isolation to prevent fire spread

The regulations for fire safety were amended in 2018 when the use of combustible materials in the external walls of relevant buildings over 18m[2] was banned – but the same didn’t apply to the roof. 

Given the many risks flat roofs are exposed to and the absence of an outright ban on combustible materials in roofs, building engineers must ensure that they are familiar with the relevant standards.

Fire safety standards for flat roofs

Even though there isn’t a comprehensive ban on combustibles within roofs, sections of ADB specifically address fire safety in roof structures, for example in the context of passive fire protection through compartmentation.

Compartment structures (including walls and floors) are fire-resistant constructions in buildings designed to delay fire moving between compartments and prevent it from spreading quickly through the rest of the building. Fire-rated compartment elements buy extra time and allow people in other areas of the building better chances of escape.

A roof can contribute to the internal spread of fire where it passes over the heads of compartment walls – which is why it’s vital to address intricate places like junctions. It’s essential to ensure fire cannot spread via the roof build-up or bypass compartments to enter new zones, nor continue penetrating through the roof structure itself.

Section 8.26 of ADB Volume 2 states, “To reduce the risk of fire spreading over the roof from one compartment to another, a 1500mm wide zone of the roof, either side of the wall, should have a covering classified as BROOF(t4), on a substrate or deck of a material rated class A2-s3, d2 or better.”

This means that the substrate – the insulation layer – must achieve a Euroclass reaction-to-fire rating of at least A2, and the roof covering across the wall junction must be classified as BROOF(t4).

A BROOF(t4) rating, however, does not relate to a fire resistance test. This classification only considers how a roof system reacts to external fire exposure when subjected to burning brands, simulated wind and radiant heat – it doesn’t assess how the system behaves in a fully developed fire. 

Roof systems containing combustible materials can achieve a BROOF(t4) rating, but running combustible insulation over the head of a fire-rated wall can prove insufficient in a fire.

To de-risk their buildings and simplify their route to compliance, a growing number of designers and developers are specifying non-combustible insulation throughout the whole roof.

Identifying suitable building products – certifications and testing

So how can specifiers be sure that the products they use meet the safety standards and building regulations for fire protection?

The simplest way to determine the combustibility of a roof insulation product, or any building material, is to verify its Euroclass reaction-to-fire rating. A non-combustible material is defined by a Euroclass rating of A1 or A2-s1, d0.

During specification, it’s best practice to verify a product’s fire safety performance by reviewing supporting evidence against the required standards. Specifiers can do so by asking for the relevant testing and product certifications. These should be easy to obtain from manufacturers. 

A quick and easy way to determine the reaction to fire rating is to refer to a Declaration of Performance (DoP) certificate. A DoP certificate signifies a product has been assessed according to a harmonised European standard and supports greater transparency in the product documentation.

By referring to performance data in DoP certificates, specifiers can verify that the product’s reaction to fire rating is appropriate for the application and meets the criteria laid out within Building Regulations and Approved Documents.

Managing fire risk in the fifth façade

Rather than having to design and specify individual zones of non-combustible insulation, developers are increasingly using non-combustible insulation across the whole of the roof. This simplifies the route to ADB compliance by avoiding the complication of using different materials across multiple zones of the same roof, all while substantially reducing the fuel load available to a fire.

To help industry professionals solidify their understanding of flat roofs fire risk, ROCKWOOL has launched a new on-demand version of its CPD on managing fire risk in the Fifth Façade that you can now take whenever is convenient for you.

Article History

Our experts continually review and update our articles when legislation changes or new information becomes available. 

Current version: 1

First published: 28/11/2022

Product Management Headshot - Lisa Stephens

ROCKWOOL Group