by Phil Slinger – CAB Chief Executive
Since the tragedy at Grenfell Tower, to many, the Government has appeared slow to react to replace dangerous cladding, but in 2019 it did implement a combustible material ban to residential buildings over 18m in height for new build in England. Today, there still remains thousands of properties requiring remedial work to remove what could be ‘dangerous’ cladding. Following a review of the fire at The Cube in Bolton in November 2019 there was much speculation as to whether the Government would lower the combustible material ban in England from 18 to 11 metres. In an update to the House of Commons, then Housing Secretary Robert Jenrick revealed that the student housing block fire in Bolton in November 2019 was technically excluded from the 18m threshold fire regulation, as the building was just 17.8 metres high.
Following the report from Jenrick and the ban on combustible materials in the external wall, stakeholders have now suggested that an 11m threshold is an acceptable limit of traditional external fire-fighting techniques. The 11m threshold was initially implemented in Scotland, but there does not seem to be any comprehensive research that supports this fire-fighting limit.
In January this year the office of the Rt Hon Michael Gove MP, Secretary of State for Levelling Up, Housing and Communities, wrote to Peter Caplehorn, Chief Executive of the Construction Products Association, requesting that the cladding and insulation companies will be held responsible for remediation work for buildings over the 11m threshold. The letter goes on to state that the Government estimate the cost to remediate unsafe cladding on buildings over 18m to be £5.1bn and for buildings between 11-18m, estimated a further £4bn spend will be required to replace dangerous cladding. The CPA currently dispute these figures as they are based purely on a desktop exercise and lack any real-world inspections. The CPA also points out that due to the nature of the contracting process it can be very difficult to determine which material has been installed, making on-site inspection necessary to determine the full extent of the cladding that needs to be replaced. The figures from the Government do not take into consideration the amount of unsafe Aluminium Composite Material (ACM) used in cladding projects compared to aluminium sheet and non-combustible insulation used in rain screen cladding, which can be perfectly safe.
Whilst the CPA are in agreement with Government that homeowners who are affected by unsafe cladding should not be expected to pay for remedial work to make their properties safe, there is no consensus at the moment as to what size the fund needs to be and how it can be contributed to. The deadline of having an agreement in place by March 2022 with CPA members in the Secretary of State’s letter of January 2022 has not been met, but a proposal has been made by the CPA to the Government in order to get a fund up and running to undertake the remedial works required to inspect and, if necessary, replace unsafe cladding. We await the final details of this fund and how it is to be formed.
As an industry we appreciate the danger of surface spread of flame in some ACM from building fires here in the UK and some well documented fires in the Middle East. So how does this affect where we are today with buildings using aluminium cladding panels and aluminium framed windows or curtain walling?
It is important to state that aluminium is non-combustible. What can be combustible is what you put on the aluminium as a finish or as a support backing. In the case of ACM, the core forming the aluminium sheet sandwich can be combustible. As aluminium melts at about 650ºC, the outer sheet of an ACM panel can quickly melt away leaving the core to burn if it is combustible. ACM has been used as a cladding material as it is cost effective and offers a perfectly flat and decorative sheet which needs little support in order for it to remain stable in use. Furthermore, ACM is easy to cut and fold, making it an ideal cladding material with good life expectancy. Today ACM sheets are still used, but with fire retardant or non-combustible cores depending on the regulations in place, making it safe for use.
Traditional aluminium rainscreen systems, normally made up of heavier gauge aluminium sheet and not ACM, are perfectly safe in use as long as the surface finish meets the desired classification to minimise surface spread of flame. If the aluminium sheet forms a cladding or rainscreen system with insulation, the components that make up the external wall of a “relevant building” (i.e. a residential building over 18m in England) must be non-combustible or of limited combustibility (i.e. A1 or A2-s1, d0, as classified by BS EN 13501-1, as per regulation 7(2)). Also very necessary are fire stops to ensure the space between cladding and structure does not act as a chimney, helping to propagate a fire. Window frames and glass are exempt from the requirement for an A1 or A2-s1, d0 classification for parts of the external wall in relevant buildings, and curtain walling framing “can be considered as a window frame”, according to the government’s FAQs on the subject. It must be noted that spandrel panels and/or other opaque insulated panels in curtain walling are not exempted and must comply with regulation 7(2). However, there remain some questions concerning the application of regulation 7(2), including the use of laminated glass, and CAB continues to work with all stakeholders to clarify the requirements.
There has also been quite a bit of discussion regarding which surface finish is required for panels to meet an acceptable resistance to surface spread of flame. Some architects are insistent a fire classification of A1 to BS EN 13501-1 must be used. In reality a classification of ‘A2-s1,d0’ is perfectly acceptable, as this offers excellent resistance to surface spread of flame and meets the requirements of current legislation.
Whilst anodised aluminium is completely non-combustible, powder coating can contain compounds which could burn. Powder coated surfaces applied at industry standard levels, normally no more than 110 microns in thickness, can be demonstrated to meet ‘A2-s1,d0’ which is perfectly acceptable on high rise “relevant” properties. This is further supported by the testing required for London Underground approval, often referred to as a barometer of fire safety. This requires compliance to the EN 45545 series, where arguably spread of flame is measured objectively (ISO 5658-2) unlike BS EN 13501-1, which involves visual assessment only. Furthermore, smoke production from powder coating is typically extremely low or non-existent (s1) with no flaming droplets (d0). On the chart of combustibility, ‘A2-s1,d0’ sits just under the ‘A1’ non-combustible classification.
A fire test for the whole external cladding system is BS 8414, which can still be used to demonstrate the safety of systems for “relevant buildings” over 11m in Scotland, alongside the requirement for materials used in the external wall to be classified A1 or A2-s1, d0 as above, but BS 8414 is not admissible for “relevant buildings” (i.e. over 18 m) in England. This test requires external wall systems that meet the performance criteria given in BRE report BR 135, which assesses whether the cladding build up is deemed safe for buildings at elevated height. The test itself involves a 9m high wall with a complete cladding installation, including the fixing of panels and insulation. It is therefore a ‘through-the-wall test’. On tests, powder coated aluminium sheet performance is perfectly acceptable and does not contribute to surface spread of flame.
The European Commission is funding work to develop a European approach to assess the fire performance of facades, and it is about to start a round-robin using the method established, which was developed from BS 8414 and DIN 4102-20 test methods, and hopes to consider falling parts and the role of a secondary opening such as a window as well as fire spread. It is intended to include curtain walling in the round robin testing. It is hoped that the European Commission will initiate a standardisation request for CEN to prepare a new test standard, but this process will likely take ten years to publish a new standard from now.
The key is getting the correct specification for cladding, curtain walling and windows completed at an early stage of building design, using the new Gateways in the Building Safety Act should help to ensure that building safety is considered at each stage of design and construction. On existing buildings, given the knowledge our members now carry, cladding systems can be quickly assessed to determine if they meet current legislation, or if they must be upgraded or possibly replaced. Our association will continue to monitor progress in the replacement of cladding and keep our members up to date with what is happening in the industry.
Based at the picturesque Bonds’ Mill development in Stonehouse, CAB staff are always on hand during normal working hours to answer any membership, training or technical aluminium fenestration related questions. News and event information is regularly updated on the CAB website at www.c-a-b.org.uk and also in the Association monthly ezine ‘A Window Into Aluminium’ which is free to sign up to. If you are not a member of CAB and wish to learn more about membership, please contact Jessica Dean at the CAB offices by email firstname.lastname@example.org or telephone Jessica at the office on 01453 828851.