Last edited 21 Jul 2017

ACM cladding

Grenfellcladding.jpg

Contents

Introduction

The term 'cladding' refers to components that are attached to the primary structure of a building to form non-structural, external surfaces. This is as opposed to buildings in which the external surfaces are formed by structural elements, such as masonry walls.

Aluminium Composite Material (ACM) panels are commonly used for cladding buildings, typically as a form of rainscreen. A rainscreen (sometimes referred to as a ‘drained and ventilated’ or ‘pressure-equalised’ façade) is part of a double-wall construction. The rainscreen itself simply prevents significant amounts of water from penetrating into the wall construction. Thermal insulation, airtightness and structural stability are provided by the second, inner part of the wall construction.

ACM cladding consist of two skins of aluminium bonded to either side of a lightweight core of polyethylene (PE), polyurethane (PUR), profiled metal or a mineral core. It is a popular product because of its precise flatness, variety of surface finishes and colours, light weight and formability. However, during a fire, the panels can delaminate, exposing the core material.

Grenfell Tower fire

ACM cladding became notorious following the Grenfell Tower fire on 14 June 2017, when ACM cladding with a polyethylene core was thought to have contributed to the rapid spread of the fire up the outside of the tower. The Reynobond PE ACM cladding used was reported by the press as being a ‘cheaper, more flammable’ option, compared to Reynobond FR, which has a fire-retardant core, or Reynobond A2 which has a non-combustible core.

ACM cladding was also linked to the Lakanal House fire in Camberwell (2009), the Wooshin Golden Suites fire in Busan (2010), the Lacrosse Tower fire in Melbourne (2014), and the Marina Torch and the Address Downtown fires in Dubai (both in 2015).

The Guardian reported that German construction companies have been ‘banned’ from using 'plastic-filled' cladding on towers more than 22 m high since the 1980s and that US building codes restrict the use of metal-composite panels without flame-retardant cores on buildings more than 15 m high. Ref: https://www.theguardian.com/uk-news/2017/jun/16/manufacturer-of-cladding-on-grenfell-tower-identified-as-omnis-exteriors

Speaking on 19 June 2017, Chancellor Philip Hammond said; "My understanding is that the cladding in question, the flammable cladding which is banned in Europe and the United States, is also banned here..." It is not entirely clear what Hammond meant by this.

He went on to suggest that; “There are two separate questions. One is: are our regulations correct? Do they permit the right kind of materials and ban the wrong kind of materials? The second question is: were they correctly complied with?"

John Cowley, managing director of CEP Architectural Facades, producer of rainscreen panels for the cladding sub-contractor Harley Facades Ltd, said: “Reynobond PE is not banned in the UK. Current building regulations allow its use in both low-rise and high-rise structures… The key question now is whether the overall design of the building's complete exterior was properly tested and subsequently signed off by the relevant authorities including the fire officer, building compliance officer and architect before commencement of the project.”

Building regulations

In England, the building regulations establish requirements for specific aspects of building design and construction. Approved documents then provide guidance for satisfying those requirements in common building situations.

The potential for fire to break out of a multi-storey building, and then to rapidly spread across external cladding is addressed in approved document B. This states that ‘The external envelope of a building should not provide a medium for fire spread if it is likely to be a risk to health and safety. The use of combustible materials in the cladding system and extensive cavities may present such a risk in tall buildings.’ As a result, materials with limited combustibility must be used in buildings with storeys more than 18 m above the ground.

Limited combustibility can be demonstrated in two ways:

Testing

On 18 June 2017, the government required social housing owners to compile lists of buildings with ACM cladding and buildings more than 18 m high and then to send samples of the cladding for fire tests.

The letter from Melanie Dawes, Permanent Secretary for the Department for Communities and Local Government (DCLG) (File:Acm cladding checks.pdf), gave the following advice on the identification of ACM cladding.

Aluminium Composite Material (ACM) is a type of flat panel that consists of two thin aluminium sheets bonded to a non-aluminium core, typically between 3 and 7mm thick. The panels can have a painted or metallic finish (eg copper or zinc effects). It can be differentiated from solid aluminium sheet by looking at a cut edge whereby the lamination is visible. It may be necessary to cut a hole in a panel if a cut edge is not readily accessible.

The Annex suggests that:

On buildings with a floor over 18m above ground level, where ACM panels are identified, it is necessary to establish whether the panels are of a type that complies with the Building Regulations guidance ie the core material should be a material of limited combustibility or Class A2.

Material of limited combustibility as described in Table A7 of Approved Document B (Vol 2) Class A2-s3,d2 or better in accordance with BS EN 13501-1.

On 21 June 2017, Melanie Dawes wrote a similar letter to owners, landlords and managers of private residential blocks offering testing of ACM cladding, paid for by DCLG. Ref https://www.gov.uk/government/publications/safety-checks-on-private-residential-blocks

On 23 June 2017, the Police confirmed that small-scale fire tests had been carried out on the Reynobond ACM cladding and the Celotex insulation used on Grenfell Tower, and both had failed. Detective Superintendent Fiona McCormack said; "The insulation was more flammable than the cladding. Tests show the insulation samples combusted soon after the test started." See also: Celotex RS5000 PIR insulation.

On 24 June 2017, the government issued a statement from Sajid Javid, the Secretary of State at Department for Communities and Local Government (DCLG) regarding the cladding testing failure rate. Ref https://www.gov.uk/government/news/statement-from-the-secretary-of-state-regarding-the-cladding-testing-failure-rate

It confirmed that all the cladding samples tested, that is, samples from 34 high-rise buildings in 17 local authority areas, had failed a combustibility test carried out by the Building Research Establishment (BRE). Fire and rescue services were asked to conduct fire safety inspections of those buildings to decide what remedial works might be required.

However the statement made clear that:

...a failure in testing of the cladding does not necessarily mean that a building will have to be evacuated; the decision by Camden Council to evacuate 4 of the 5 towers on the Chalcots Estate was because the failed testing of the external cladding was compounded by multiple other fire safety failures which the fire inspection team found within the buildings.

On 24 June 2017, Reuters reported the guidance set out in a 2016 Reynobond brochure:

When conceiving a building, it is crucial to choose the adapted products in order to avoid the fire to spread to the whole building. Especially when it comes to facades and roofs, the fire can spread extremely rapidly… As soon as the building is higher than the fire fighters’ ladders, it has to be conceived with an incombustible material.

However, the Reuters article suggests that Arconic, the US company that supplied the cladding panels for Grenfell Tower may have known that it was a tall building when bidding for the project in 2014. Ref https://www.reuters.com/article/britain-fire-arconic-idUSL8N1JK2TZ

On 26 June 2017, Arconic announced that it was discontinuing sales of Reynobond PE for use in tower blocks. The statement said:

We believe this is the right decision because of the inconsistency of building codes across the world and issues that have arisen in the wake of the Grenfell Tower tragedy regarding code compliance of cladding systems in the context of buildings’ overall designs.

On 26 June 2017, in a statement to the House of Commons, Sajid Javid announced the creation of the Grenfell Tower independent expert advisory panel to advise the government on the fire.

By 27 June 2017, 75 cladding samples had 'failed' the fire tests being undertaken - 100%. Fire safety experts then began to question what sort of testing was being carried out, pointing out that it is the entire cladding assembly that needs to be tested, not just small samples, and suggesting the building regulations do not require that cladding panels achieve a Class A2 rating if the entire cladding system meets the standards set out in BS 8414. Concern was also expressed that removing cladding from buildings could compromise any insulation that was exposed.

On 28 June 2017, with 120 cladding samples having 'failed' tests, the National Housing Federation chief executive David Orr suggested the tests should be stopped, and the focus shifted to considering how to make people feel safe in their homes.

On 29 June 2017, Theresa May announced that Sir Martin Moore-Bick had been appointed to lead a Public Inquiry into the fire. For more information see: Grenfell Tower Inquiry.

On 30 June 2017, the BBC and the Times reported having seen documents showing that the original cladding specified for the Tower had been a zinc cladding with a fire-retardant core, but in 2014 this was changed to ACM cladding with a PE core to save £293,000 and to allow a change of colour.

However, the BBC point out that ‘both types of cladding have the same official fire rating’ (it is not clear what is meant by the word ‘official’) and there was ‘no suggestion a deliberate decision was made to cut fire safety’. Ref http://www.bbc.co.uk/news/uk-40453054 and https://www.thetimes.co.uk/edition/news/keep-costs-of-cladding-down-grenfell-tower-experts-told-6qrhmwzxv

By 2 July 2017, DCLG were reporting that 181 samples of cladding had 'failed' fire tests - 100% of those tested.

In a statement to the House of Commons on 3 July 2017, Sajid Javid said:

...we ourselves have asked questions about the testing regime after discovering the 100% failure rate so far.

Last week I asked for the testing regime to be independently assessed.

This was carried out by the Research Institutes of Sweden, and they have confirmed they believe the process to be sound.

A full explanatory briefing note on the testing process is available on GOV.UK.

As the note explains, every failed test means the panels are unlikely to be compliant with the limited combustibility requirement of the building regulations guidance.

This has been confirmed by legal advice and the advice of the independent expert panel that was established last week.

For use of the panels to be safe landlords need to be confident that the whole wall system has been tested and shown to be safe.

We are not aware of any such system having passed the necessary tests, but I have asked the expert advisory panel to look into this further.

Ref https://www.gov.uk/government/speeches/update-on-grenfell-tower-fire-and-fire-safety

The Government building safety programme - explanatory note referred to in the statement says:

The Department’s view, supported by expert and legal advice, is that external walls in a tower block can meet the Building Regulations requirement for resisting fire spread in two ways....
  • The first is for each individual component of the wall (insulation, filler, etc) to be of limited combustibility, and to each meet set standards for this.
  • The second is to ensure that all the combined elements of a wall, when tested as whole system, have sufficient fire spread resistance to meet a set standard.

The tests being conducted at BRE are testing only whether the core or filler of ACM panel samples being submitted are of a type that would fail the limited combustibility test for an individual element of a wall in a tall building (the first of the requirements summarised above).

It is possible, therefore, that ACM panels that have a core material that is not of limited combustibility, might be safe if installed as part of a whole wall system that meets the second test described above.

See also: ACM cladding testing by BRE.

At the third meeting of the Independent Expert Advisory Panel, they suggested drawing attention to the need to ensure recladding work complies with all Building Regulations’ requirements, including; structural safety, resistance to moisture penetration and build up, and energy - as well as ensuring fire safety. As a result, on 13 July 2017, a letter was sent from the Department for Communities and Local Government (DCLG) to all building control bodies in England including approved Inspectors. Ref https://www.gov.uk/government/news/ensure-that-recladding-work-meets-building-regulations-advises-expert-panel

Further tests

On 6 July 2017, the Grenfell Tower independent expert advisory panel advised that further testing should be carried out by BRE to establish how different types of ACM cladding behave in a fire in combination with different types of insulation. This, they suggest will help landlords decide what further measures may be needed to make their buildings safe.

The tests will look at 6 combinations of 3 different types of ACM cladding, with polyethylene, fire retardant polyethylene, and non-combustible mineral cores, combined with insulation of rigid polyisocyanurate foam and non-combustible mineral wool. The tests will be carried out in accordance with BS 8414, and involve building complete cladding systems 9 metres tall and then subjecting them to a severe fire. The results will be made publically available, but landlords should take professional advice on the implications for their buildings.

Ref https://www.gov.uk/government/news/expert-panel-recommends-further-tests-on-cladding-and-insulation

Following this announcement, two housing associations in Salford stopped cladding removal work on a number of tower blocks. Executive director of operations at Salix Homes, Sue Sutton said " ...advice regarding the removal of cladding is now unclear and there is conflicting information about the need to remove the panels."

Communities Secretary Sajid Javid made an oral statement to Parliament on 20 July 2017, giving an update on the government response to the fire. He said that "...no more than 208 local authority and housing association residential blocks over 18 metres tall have been fitted with aluminium composite material cladding. 189 of these have had cladding samples tested by the Building Research Establishment, they’ve been tested by proxy or they have already had taken their cladding down. None of them have passed the limited combustibility test." https://www.gov.uk/government/speeches/statement-on-grenfell-tower-20-july-2017.

DCMS also published an explanatory note on the large-scale testing. File:20170720 Explanatory note on large scale testing FINAL.pdf. This suggested that the first results would be expected in the week commencing 24 July 2017 and will be made public on the DCMS website. The testing cycle is around eight days for each wall - including construction, setting up and undertaking the test, and deconstructing the wall.

Week commencing Advice expected on:
24 July 2017 ACM with unmodified polyethylene filler with PIR foam insulation
31 July 2017 ACM with unmodified polyethylene filler with mineral wool insulation
ACM with a fire retardant polyethylene filler with PIR foam insulation
7 August 2017 ACM with a fire retardant polyethylene filler with mineral wool insulation
14 August 2017 ACM with a limited combustibility filler with PIR foam insulation
ACM with a limited combustibility filler with mineral wool insulation

However, the tests are only illustrative of how different systems might behave. Building owners will still need to take their own professional advice on what steps to take depending on the materials they have on their buildings.

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Comments

Quote from this article -

Detective Superintendent Fiona McCormack said; "The insulation was more flammable than the cladding. Tests show the insulation samples combusted soon after the test started."

So why does the article concentrate almost exclusively on the cladding and not the insulation when it appears that the insulation was the main fuel for the fire, not the cladding ?