A critique of the Building Research Establishment’s advice on cladding after Grenfell

A typical cladding test rig used by BRE

The government responded to the Grenfell Tower fire by taking action to ensure the safety of high-rise buildings and their residents. Landlords were asked to test their Aluminium Composite Material (ACM) cladding to see if it was combustible or not. The testing process, which was conducted by the Department for Communities and Local Government (DCLG) at the Building Research Establishment (BRE), involved examining the filler material in the panel's core. If the panel failed the test, landlords were instructed to take interim fire safety measures as outlined by the government in June 2017.

The testing equipment and procedures followed the BS EN ISO 1716:2010 standard, but not all the steps in the standard were necessary for this screening process. An expert panel was also established to advise the government on further actions to improve fire safety. By July 2, 2017, all 181 samples of cladding that were tested had failed. On July 6, the expert panel recommended further testing by BRE to see how different types of ACM cladding and insulation perform in a fire. These tests involved building full cladding systems and exposing them to a severe fire according to the BS 8414 standard.

The tests examined six combinations of three different types of ACM cladding, including polyethylene, fire-retardant polyethylene, and non-combustible mineral cores, combined with insulation made of rigid polyisocyanurate foam and non-combustible mineral wool. These cladding systems, which were built to a height of 9 meters, were subjected to severe fires in accordance with the BS 8414 standard. The results of the tests were made public.

BRE test results

Here is a summary of what I understand from the test results: 

1. The first test, conducted on July 28, 2017, found that a system comprising ACM cladding with polyethylene filler and foam insulation did not meet building regulations. 82 buildings are believed to have this system. Following these results, the government issued additional advice for landlords of affected buildings.

2. The second test, conducted on August 2, revealed that a system consisting of ACM cladding with a polyethylene filler and stone wool insulation did not meet building regulation guidance. There are 111 buildings known to have this system. They were advised to take remedial action. 

3. The third test, conducted on August 8, found that a system comprising ACM cladding with a fire-retardant polyethylene filler and PIR foam insulation did not meet current Building Regulations. There are 13 buildings in England over 18 meters tall with this system. The government also commissioned a seventh test on ACM cladding with fire retardant polyethylene filler and phenolic foam insulation.

4. The fourth test, conducted on August 11, revealed that a system comprising ACM cladding with a fire-resistant polyethylene filler and stone wool insulation was compliant with Building Regulations when installed and maintained properly. There are 13 buildings in England over 18 meters tall with this system. It is unclear what action was taken on these buildings. 

5. The fifth test, conducted on August 14, found that a system comprising ACM cladding with a limited combustibility filler and PIR foam insulation was compliant with Building Regulations. The government is not aware of any buildings in England over 18 meters tall with this system.

6. The sixth test, conducted on August 21, revealed that a system consisting of ACM cladding with a fire-retardant polyethylene filler and phenolic foam insulation did not meet Building Regulations. There are 22 buildings in England over 18 meters tall with this system.

7. The seventh and final test, conducted on August 24, found that a system comprising ACM cladding with a non-combustible mineral core and stone wool insulation was compliant with Building Regulations. There are no buildings in England over 18 meters tall with this system. Landlords of buildings with cladding systems that have failed these tests have been advised to take appropriate safety measures and seek professional guidance.

Therefore, BRE advised the government that three types of cladding and insulation combinations did in fact satisfy the building regulations (and were therefore deemed safe), but is this accurate?

A critique of the testing process

The approval process for cladding systems on high-rise buildings often involves referencing large-scale British Standard tests, such as BS8414. These tests are necessary because the cladding systems may contain combustible materials that are separated from the fire by other materials for a certain period of time. In order to accurately test the safety of these systems, the test specimen must accurately represent the way in which the system will be installed in real life. However, there may be concerns that this criterion is not being met in certain cases.

The BS8414 test, which is used to evaluate the suitability of cladding systems for use on high-rise buildings, involves a large wood-crib fire that simulates a compartment fire breaking through a window and threatening the exterior cladding. I do not believe these test conditions replicate the installation of cladding in the real world. There are five main areas of concern regarding the adequacy of this test:

1. The relevance of the fuel load to modern materials and lifestyles: The fuel load used in the test may not accurately represent modern fires, which often contain a high percentage of plastic-based fuels that can raise flame temperatures and lengthen flames. This could affect the ability of the test to accurately assess the performance of cladding materials, such as aluminium, which becomes weaker at high temperatures.

Fire plume differences between materials 

2. The impact of un-fire-stopped vents and ducts on the cladding system: The test does not take into account other breaches in the cladding system, such as windows, vents, ducts, or pipes. These openings can allow fire and toxic by-products to spread into the cladding system's void, where combustible materials may be located. This could affect the ability of the test to accurately evaluate the performance of the cladding system in real-life situations.

3. The provision of oxygen to materials and the occurrence of "chimney effects": The test may not accurately simulate the flow of oxygen within the test specimen or the occurrence of "chimney effects," which can accelerate the spread of fire. This could be due to factors such as the sealing of test piece edges, the proximity of fire stops, the absence of vents, and the use of non-representative void depths.

4. The performance of cavity barriers: The test does not take into account the ignition properties of all materials that cavity barriers separate, only the external cladding material. This could affect the ability of the test to accurately evaluate the performance of cavity barriers when exposed to direct flame challenges or when separating materials with different ignition properties.

5. The performance of insulation materials: The test may not accurately evaluate the performance of insulation materials because it does not take into account the presence of fire stops or the impact of different ignition properties on the spread of fire.

Accordingly, it is my opinion that the BS 8414 test does not provide sufficient assurance that cladding systems tested to its standards will meet necessary fire safety requirements. Ideally, the British Standards Institution (BSI) should conduct a review of the BS8414 standard or develop an alternative test that is approved by insurers.

Discussion and summary:

While BRE suggests that some of the current cladding systems do adhere to the building regulations, I believe the testing methods are not representative of in-situ applications. Therefore, some of the cladding(s) used on high-rise blocks (and other buildings such as hospitals and schools) currently deemed “safe” may in fact be a ticking time bomb. I cannot find any information online about whether buildings with "safe" cladding systems have undergone any remedial work in the aftermath of Grenfell. While most buildings with ACM insulation have been remedied since 2017, what about buildings with limited combustibility fillers and 'fireproof' insulation defined by the clearly insufficient BS8414 standards? New government legislation which bans combustible materials in external insulation on high-rise structures has not been applied retroactively and therefore some buildings pose a danger to life. I have been unable to find data about the number of non-high-rise structures in the UK which use cladding that may be erroneously regarded as safe. 

To surmise, the test fires used in evaluating the safety of existing cladding systems only involve wood, while real fires often involve a significant percentage of plastic materials. Additionally, the cladding materials tested are typically sealed units, while in real life they may have gaps and cover a larger area. The materials tested are also in their manufacturers condition, but during actual use may be punctured by vents or ducts and deteriorate over time. Furthermore, the cladding application may not follow the manufacturer’s specifications as installers may lack relevant qualifications. These are just some reasons why the Building Research Establishment (and by extension the government) may have given a false impression about the safety of cladding still in use in the UK. We do not need another Grenfell disaster.