Fire Resilience
Standards & Regulations

Understanding flat roof fire safety building regulations

Lisa Stephens, Product Manager – Building Envelope
Lisa Stephens, Product Manager – Building Envelope
April 9, 2024

Legislation and guidance for the fire safety of high-rise buildings has been evolving consistently over the last few decades – and never more prominently than since the Grenfell tragedy in 2017. This proved to be a watershed moment around the use of non-combustible materials in the external walls of relevant buildings of 18m and over, and the industry has generally looked favourably upon the changes.

However, legislation covering flat roofs on high rise buildings has not necessarily received the same attention. For flat roof applications, specifiers and contractors must navigate a series of sources including the Building Regulations, Approved Documents, Technical Guidance documents, and recently Building Safety Act 2022.

This article will draw on the latest ROCKWOOL whitepaper, ‘Flat roofs: The functional fifth façade’, to shed light on mandatory regulations versus guidance in high rise flat roofs. 


Building Regulations for flat roofs

As the central source of truth for UK construction requirements, it is the responsibility of those designing and carrying out building works to meet the statutory requirements of the Building Regulations.

This is often confused with meeting the guidance of approved documents, such as Approved Document B (ABD) in relation to fire safety in England – especially as ADB makes reference to specific building types and heights, and where factors including compartmentation may affect specification requirements. Critically, ADB states:

“Although approved documents cover common building situations, compliance with the guidance set out in the approved documents does not provide a guarantee of compliance with the requirements of the regulations because the approved documents cannot cater for all circumstances, variations and innovations.”

Returning to the Building Regulations, the primary requirement that flat roof stakeholders must be aware of is B4:2: “The roof of the building shall adequately resist the spread of fire over the roof and from one building to another, having regard to the use and position of the building.” Notably, this requirement does not specify ‘height’ as a defining factor, in contrast to B4:1 in relation to external walls which does cover height.


Using flat roof fire safety guidance

Looking beyond the Building Regulations, guidance documents such as ADB are undoubtedly a useful – if not binding – resource for designers and contractors. ADB supports by providing practical ways to achieve compliance with the statutory requirements in common constructions, but acknowledges that it cannot be all-encompassing.

It is important to note, however, that in light of the Building Safety Act 2022 it may not be sufficient to simply follow this guidance. Even if it is an exact model of the construction offered in ADB. The Building Safety Act 2022 reinforced liabilities for all stakeholders, directing that compensation can be claimed from anyone responsible for any defective work including builders, contractors, architects and designers. Crucially, it states that it is not a valid defence for the defendant to claim to have followed established practice at the time[1].

Responsible parties must consider carefully whether their specific project adheres to the statutory requirements rather than to the guidance alone. In relation to roofs and façades, designers should be vigilant regarding all potential fire risks. Threat of fire from above the roof is considered in classifications such as BROOF(t4) (BS EN 13501-5), but exposure to fire from below the roof may not always be adequately addressed. The absence of fire stopping seals to building services and penetrations that pass through the roof may create paths for fire to spread to the roof, from below.

In practice, for a designer, this means finding construction products that have been subject to relevant performance testing for their application. Manufacturers may signify that their products meet BROOF(t4) as a general standard, but valuable suppliers go further to provide specific application guidance and will work directly with interested specifiers and architects to deliver bespoke technical support. For a deep dive into relevant testing and certifications, head over to our article: The importance of product testing and certification in mitigating flat roof fire risk.

[1] ¹ UK Government: Building Safety Act 2022

Achieving building regulation compliance

Flat roof stakeholders must work diligently to ensure that they uphold the statutory requirements of the Building Regulations at all times. In terms of selecting and installing compliant products, working with a reputable and transparent manufacturer that clearly presents its testing and certifications is a clear benefit.

To explore this topic in more detail, and to see how legislation and guidance affects common flat roof installations including solar PV and social spaces, download the ROCKWOOL whitepaper ‘Flat roofs: The functional fifth façade’.

Download the whitepaper now. 

Webpage history

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

First published: 09/04/2024