Geoff Wilkinson is shocked by revelations in fire safety reports the government has sat on for three years
The aluminium composite material (ACM) cladding scandal that came to light following the Grenfell Tower tragedy continues to dominate headlines and regulatory change in 2019. By now most readers will be aware that the government has published amendments to Part B of the Building Regulations, restricting the use of combustible materials in the external walls of certain buildings over 18m in height.
The current restrictions apply to the external walls of buildings with residential uses, such as blocks of flats, student accommodation, care homes, sheltered housing, hospitals and dormitories in boarding schools. The new requirement means that all materials forming part of an external wall or specified attachment must achieve a fire rating of European Class A2-s1, d0 or Class A1.
However, if you think it is only ACM cladding that is at issue you may be surprised to learn that it has been revealed that zinc composite material (ZCM) used as cladding is also now under scrutiny. This month the government’s Building Safety Programme will commence a series of tests on other forms of cladding, including zinc, to see whether they pass the BS 8414 test, following indications that these, too, may be combustible. As a result, it is now believed that there could be as many as 1,678 more at-risk sites over 18m with combustible cladding than was previously believed.
The government has also finally put in the public domain a series of legacy reports commissioned in 2014 which raise much wider concerns regarding the potential for fire spread in buildings erected using modern construction methods. In particular, a BRE report entitled ‘Compartment size, resistance to fire and fire safety project work stream 3’ raises significant concerns over everyday construction methods.
BRE report ‘Compartment size, resistance to fire and fire safety project work stream 3’ raises significant concerns over everyday construction methods
The report (issued by BRE prior to the Grenfell fire) warned that while, historically, there had only been a limited number of fatalities that could be directly associated with fire or smoke spread in concealed spaces, those cases showed that the potential risks and losses remained high.
The report concluded that new and innovative methods of construction introduce additional voids, cavities and shafts into buildings as part of the construction process.
This gives rise to issues associated with the provision and quality of installation of fire protection products and systems in concealed spaces. Architects should look in particular at Section 5 of the report, which reviewed a number of case studies of actual fires in low-rise residential developments (which, remember, are not covered by the current ban) with some shocking revelations.
In the first case study, a fire reportedly started within the external wall void of a three-storey timber-framed residential building simply due to a nail penetrating a lighting cable. The external façade was an insulated cladding system and fire spread up the building through the internal cavities and the external cladding.
In another case, again involving a three-storey timber-framed block of flats, the fire spread through the cavities up and along the front face of the building. The fire then spread up to the roof space, downwards internally and laterally through the roof area. The fire spread led to the collapse of roof trusses and the ceiling.
Ad-hoc fire tests carried out by BRE indicated that everyday building products such as the breather membrane contributed to fire spread within the cavity, while bituminous material spanning the roof beneath the tiles contributed to fire spread within the roof space.
Another case involved a fire within one of the ground floor flats of a four-storey timber-framed block of flats. The fire brigade extinguished the fire and, before leaving the scene, checked the area with a thermal imaging camera to ensure there were no hidden hot spots. But they were called back an hour or so later, as the fire had reignited within the external wall cavity and spread into the roof space, ultimately leading to the collapse of the building (pictured).
The investigation found causes of the fire spread included timber battens used to bridge the cavity in line with the compartment floor levels, which were wrapped in a bituminous damp-proof material to prevent moisture ingress. Furthermore, the sheathing layer was a low-density bitumen-impregnated fibre board identified as the one of the worst-performing products of those tested by BRE using the BS EN ISO 11925-2 small flame test.
These case studies have highlighted that it is not just high-rise buildings that are at risk and that the potential for everyday products such as timber battens and plastic vents can act as a potential route for fire spread. Specifiers should consider the risks associated with the location and selection of materials for any products forming or penetrating the external building envelope, with non-combustible materials always being the safest option if there is any doubt.
Geoff Wilkinson is an Approved Inspector and managing director of Wilkinson Construction Consultants www.thebuildinginspector.org