Following the devastating fire which ripped through 24-storey Grenfell Tower on 14 June, blame quickly fell on the building’s overcladding.
Communities secretary Sajid Javid then ordered safety checks for aluminium composite material (ACM) cladding used on all social housing across the UK.
On 21 June, building research and testing body BRE began testing samples of aluminium composite material (ACM) cladding to see if its core met a specific level of fire resistance. At the time of going to press, cladding samples from 200 buildings across the country had been tested – and all had failed this particular test, and further testing has been recommended.
So what exactly is the test? And how, given the 100% failure rate, was this type of cladding signed off as meeting building regulations in the first place?
As fire service firm Hilti fire engineer Alastair Brockett explains, there are no clear answers in fire testing.
“The whole thing about testing gets very confusing because there are so many different types of fire test, and they determine a particular performance and/or response to fire,” he says.
Under requirement B4 (1) of the Building Regulations 2010, it is stated that: “The external walls of the building shall adequately resist the spread of fire over the walls and from one building to another having regard to the height, use and position of the building”.
This is the regulation which must be met. But it is not that simple, as there are several options for complying with this requirement.
OPTION ONE: PRODUCT TEST
One option is to follow guidance set out in Approved Document B, the government’s own text offering advice about how to comply with building regulations. By using materials of “limited combustibility” for buildings taller than 18m and providing adequate cavity barriers, clauses 12.6 to 12.9 of Approved Document B are met.
Appendix B of the document gives a definition of limited combustibility. It says a material sample must meet testing criteria described in BS476-11, although the British Standard can be substituted with equivalent European codes such as BS EN13501-1:2007, which is used to classify fire resistance in construction products.
BRE is currently screening ACM cladding samples for limited combustibility based on testing methodology detailed under BS EN ISO 1716:2010, one of a suite of standards published under BS EN 13501-1:2007. During the test, cladding samples are burnt in a pure oxygen atmosphere to determine the gross heat of combustion. From the results the samples are then given a one to three rating, where a two or three grade indicates a failure to meet requirements.
However, BRE has made clear that its test uses a limited interpretation of BS EN ISO 1716:2010, meaning it simply needs to set fire to the core material in each ACM panel to determine whether panels pass or fail the test.
OPTION TWO: FULL SCALE TEST
Approved Document B offers another way to comply with building regulations, given in clause 12.5. This involves holding a bespoke fire test of a full scale proposed external cladding system, as specified in BS 8414-1 and BS 8414-2. It is this test that has now been recommended the government’s expert panel on fire safety, set up in the wake of Grenfell. The data generated by the test must then show that the system meets performance criteria set out in BR135 – Fire Performance of External Thermal Insulation for Walls of Multistorey Buildings.
Unlike Option One, Option Two tests the way fire spreads across a full cladding system, rather than a small sample. Therefore the entire cladding system is being tested, not just one part. It means that, technically, a cladding system could include material which would not pass testing under Option One, but would under Option Two.
OPTION THREE: DESKTOP STUDY
There are alternative sources for guidance for how to comply with building regulations. For example, in 2015, the Building Control Alliance (BCA) released guidance for meeting building regulations for buildings exceeding 18m.
Under this third option, a desktop study can be carried out in place of an expensive physical test. The BCA guidance states that a desktop study must come from a suitably qualified fire specialist and must state whether, in their opinion, the proposed system would comply with BR135 criteria.
OPTION FOUR: WHOLE BUILDING TEST
Finally, if none of the other options is suitable, a fourth option offers a holistic fire engineer approach – meaning that the building’s geometry, ignition risk and other factors limiting the spread of fire are taken into account and a building is assessed by a fire engineer. Any fire engineer approach would have to follow recognised design codes.
So, testing a building component, like a cladding sample, or testing how well part of a building would resist fire as a whole, are both options to meet building regulation requirements. This explains how two tower blocks in Bootle on Merseyside were able to comply with building regulations, but fail the BRE’s test.
QUESTIONS RAISED BY TEST PROGRAMME
Communities secretary Sajid Javid has said the failure rate has “underlined the value of the testing programme”. But this test programme has raised legitimate questions about the validity of guidance and building regulations.
“This has brought into question everything that surrounds the environment of testing construction methodologies,” says Barry Turner, who is director of technical policy for building control professionals representative body Local Authority Building Control.
Meanwhile Brockett argues advice in Approved Document B (ADB) should be clearer. “There are many things in ADB which need to be addressed; some just tightened up, just small tweaks, other things, a serious overhaul I would say,” he says.
Grenfell | Tower blaze highlights building regulations flaws