The most common cause of death from fires is smoke inhalation. And for every fatality, many more are likely to be hospitalised.
Allan Hurdle believes architects should be specifying smoke-limiting s1 wall membranes for a wide range of buildings, such as schools, hospitals and care homes. Especially where residents’ mobility may be limited.
Hurdle hosts an on-demand RIBA CPD webinar on A2 Limited Combustible Membranes (LCM) and is a technical consultant to the Serge Ferrari Group.
In the webinar, he points out that membranes offering high levels of smoke protection give occupants time to be evacuated more safely, without being overcome. Just three breaths of toxic smoke can be enough to lead to unconsciousness.
What are non-combustible breather membranes?
A new generation of limited-combustibility and smoke-blocking wall membranes have been developed since the Grenfell Tower fire. They are increasingly used for recladding and new buildings and are fire-resistant to Euroclass A2.
These breathable membranes have a fire resistance of A2-s1,d0.
- Class A2 denotes very limited combustibility
- Class S1 guarantees very limited smoke
- d0 guarantees no burning droplets that can spread fire.
Wall membranes of this kind dramatically restrict deadly smoke transmission into buildings, and can also offer the advantages of rainscreening and breathability.
The first of these non-combustible breather membranes in the UK to be independently tested to EN 13501-1 was Stamisol Safe One. Other manufacturers such as Du Pont, Effisus and Cortex have since introduced A2-s1,d0 membranes.
This provides a performance above that required by current regulations. And when it comes to lower-risk buildings, regulations state that membranes used as part of an external wall construction above ground level must achieve a minimum of Class B-s3, d0. That is well below the A2-s1,d0 level.
Are wall membranes exempt from the combustible materials ban?
Anyone who specifies construction materials will almost certainly be aware of the ban on combustible materials on the external walls of buildings, introduced in 2018.
Part B4 of Approved Document B Regulation 7(2) relates to fire spread in buildings over 18 metres. It states that all materials forming part of an external wall system must achieve Euroclass A2 or the higher, non-combustible A1.
But there is an exemption for some materials - including membranes.
Nevertheless, Hurdle recommends that if a building’s cladding is being upgraded to A2-s1,d0 levels it makes sense to upgrade membranes to A2-s1,d0 at the same time. This provides the building with a complete A2 fire-rated system. Existing wall membranes in place are likely to be the much lower-rated Euroclass E or B.
The advantages of breathability
“If you are selecting a membrane, you should be now looking for an A2 breathable and waterproof membrane with UV protection,” Hurdle advises. “You should also be looking for an installer that can demonstrate competence.”
A typical wall build might be brick, thermal blockwork, membrane and cladding. An A2-s1,d0 membrane will be a glass-fibre membrane (similar to the non-combustible A1) with a specialised coating to provide waterproofing and breathability. Hurdle advises architects to look for a water resistance rating of W1, which offers the blockwork rainscreening protection from driving rain.
For new builds, a breathable membrane will allow moisture to escape from the newly-laid thermal block layer as well as allowing long-term moisture transfer. Breather membranes such as Stamisol Safe One can be used both for closed and partially open vertical facades with up to 50mm joints, or with an open area of up to 50%.
Will the re-cladding programme have an impact on all buildings?
Hurdle predicts that recladding programmes are going to be running for many years. Following the Grenfell Tower fire, 2820 higher-risk residential buildings were identified as having potentially dangerous cladding. Four years later, fewer than 500 had been surveyed and confirmed as candidates for recladding.
He also anticipates that client expectations about non-combustible materials will, over time, impact low-rise buildings too - and not just residential ones. There are hundreds of fires recorded in schools alone in the UK every year.
“We don’t actually know at this time how many buildings are fitted with combustible cladding materials,” Hurdle reflects. “Changing cladding systems without changing combustible membranes is a missed opportunity, and could be a disaster waiting to happen.”
Thanks to Allan Hurdle, CEO, AKH Services Ltd.
Text by Neal Morris. This is a Professional Feature edited by the RIBA Practice team. Send us your feedback and ideas
RIBA Core Curriculum topic: Health, safety and wellbeing.
As part of the flexible RIBA CPD programme, professional features count as microlearning. See further information on the updated RIBA CPD core curriculum and on fulfilling your CPD requirements as an RIBA Chartered Member.
