Fire safety issues in the building envelope

With the Grenfell disaster approaching its fifth anniversary, the Mayor of London has criticised the current approach to designing and implementing building safety, reflecting the views of many in the housing sector. Allan Hurdle, CEO of AKH Services, highlights the urgent need to establish best practice and explains why concerns remain over the area of risk which was central to Grenfell.

The Mayor of London, Sadiq Khan, recently announced a significant intervention in the regulation of fire safety in buildings. A new public consultation on draft guidance that puts fire safety at the centre of the planning process for new developments, the London Plan Guidance (LPG) aims to ensure that fire safety is considered at the earliest design stage of a development and addressed in planning applications to ensure the most successful outcomes are achieved for building occupants and users. LPG will consider a range of developments, including alterations to external walls.

Sadiq Khan said:

“The current building safety situation is a scandal, and I am concerned that almost five years after the tragedy at Grenfell Tower, it appears that the Government are still not willing to properly address it. That’s why I’ve been using all the tools at my disposal to raise the standard of fire safety measures in London, through requirements for developers in my London Plan and lobbying developers and building owners to share vital fire safety information with residents.”

There has been much discussion about the contentious issue of who should pay for the safety upgrades. Thousands of leaseholders have been facing huge costs to fix dangerous cladding, but government has signalled a significant shift in its stance this year: Housing Secretary, Michael Gove, has outlined a raft of amendments to the Building Safety Bill which will require developers, manufacturers and building owners to pay for the £4bn estimated remaining cost to replace unsafe cladding.

That change brings welcome relief for leaseholders and more clarity to the question of who pays for the mandatory remediation, but another important question has not yet been definitively answered: does the mandatory remediation go far enough in improving safety? Sadiq Khan is one of an increasing number of high-profile figures expressing doubt about the answer. His comments reflect concerns widely shared within the housing sector about the extent of current regulations and whether they are maximising protection against fire.

While cladding has been a focal point in the tightening of regulations, another area of potential risk has avoided the spotlight. Laws introduced in response to Grenfell require a building’s outerwall system to have a minimum Euroclass A2-s1,d0 fire safety rating, denoting limited combustibility. However, breather membranes installed behind the cladding are subject to less stringent standards. Approved Document B Volume 2 (Aug 2019) states that “there is no requirement for membranes which are part of external wall construction over 18m for any building to be limited combustible.” Membranes are currently exempt from being part of an A1 or A2-s1, d0 vertical wall system.

It’s a curious discrepancy: breather membranes represent a large component of the building envelope, comparable in surface area to cladding, and therefore logic dictates that these elements should meet the same levels of fire retardancy. So why is the regulation inconsistent?  It’s largely due to the complexities involved in developing A-rated systems at the time when the legislation was drafted. In the past, there have been challenges in manufacturing breather membranes that could meet the non-combustibility or limited combustibility of Euroclass “A” to  BS/EN13510-3 without compromising their breathability to BS5250 standards with water resistance to W1 standards, negating their primary functions in controlling moisture, reducing condensation and protecting against rainwater.

That may have been the case in 2017, but the construction industry has always evolved through innovation. Advances in design have raised the bar for sustainability; they have the potential to achieve the same for safety with life-saving improvements to this vital area of building performance. We have now reached the point where the development of breather membrane technology has overtaken legislation by redefining what is possible.

I have been consulting the companies that are driving advances in the development of breather membrane technologies. Manufacturers and suppliers in Europe include the Serge Ferrari Group in Switzerland and ITP in the UK. They are currently offering breather membranes which are Euroclass A2, W1-rated for waterproofing and breathable to BS5250. Their discussions with developers, contractors and façade specialists suggest that opinion across the sector is increasingly in favour of fully A2 -rated external wall systems. The prevailing view echoes the straightforward logic underpinning the discussion: if the technology is available, then why not use effective A2-rated membranes which are waterproof, breathable and offer a high UV level to enhance safety in buildings?

It’s worth noting certain distinctions which apply to different ratings within the Euroclass A classification in the context of breather membranes.  Euroclass A1 membranes have been developed for non-combustibility, with no smoke and no hot droplets, but they are limited in breathability. A more effective all-round solution is a Euroclass A2-s1, d0 limited-combustibility membrane providing additional breathability to remove moisture. It also provides W1 waterproofing to EN ISO 20811, enabling building protection over and above the capabilities of an A1 membrane, while exceeding the requirements of Approved Document B part 4 which is in need of updating for building safety. A good A2 rated membrane will also offer 5,000 hours of UV resistance to EN ISO 13859-2.

Those nuances reflect the broad complexity of breather membranes. Assessing different areas of performance can be a challenge, so it is vital to use all the technical resources available. Most importantly, products should be supplied with comprehensive and transparent data on combustibility, breathability and water resistance with reference to the relevant standards. The data should be independently certified by authorised testing bodies. The Grenfell Tower Fire Investigation discovered the use of non-compliant products and a lack of independent testing.  It exposed the need for a more rigorous specification process and, with that in mind, no breather membrane should be considered without certified evidence of fire safety tested to EN13501-1 which forms the basis of Euroclass standards.

Sadiq Khan and others are advocating a fire strategy which drives the widespread adoption of practices serving a clearly defined building safety concept. To achieve that goal, it is vital to provide education and support throughout the construction supply chain to ensure that specifiers make informed decisions and installers have the key competencies needed to play their part.

BSI, in its role as the UK National Standards Body, opened a public consultation in December 2021 for PAS 8671, a new framework for competence of individual Principal Designers and designated individuals working under the Organisation Principal Designer. The consultation sought input from residents and experts in the housing, construction, fire, and safety industries to develop a new standard as a part of the Built Environment Competence Programme, which supports the government’s Building Safety Bill to raise competence requirements for three newly regulated roles: Principal Designer, Principal Contractor and Building Safety Manager. The conclusions will help to define future best practice and, together with the Building Safety Bill,  they are likely to apply formal responsible responsibilities across the supply chain. If so, it could spur collective will to ensure that existing and new buildings meet the highest fire safety standards. Designers, consultants and Installers should adopt “best practice” when it comes to A2 membranes being fitted over the current B S3 class.

When the Grenfell disaster happened five years ago, the problem of dangerous building façades became a catalyst for change. There is no doubt that, in this critical area of risk, the time is ripe to review the regulations and guidance to ensure that we are doing everything possible to keep building occupants safe.

With hundreds of existing high-rise buildings still in need of façade replacement, there is no better time than now to start that process.

Regardless of how the latest legislation unfolds, best practice should be adopted without the need for regulatory enforcement – Grenfell taught us that compromising on standards can have fatal consequences.