Sunday20 August 2017

Grenfell Tower: Should this cladding be allowed?

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The rapid and devastating spread of the fire at the west London tower has raised questions whether ACM cladding should be permitted on high-rise residential towers, says Thomas Lane

T Lane

The tragedy unfolding in west London has focused minds on the fire performance of tall residential buildings like never before. As fire crews comb through the wreckage of Grenfell Tower there is awful sense of dread as so many people remain unaccounted for, in some cases whole families. It is likely this fire, and the associated loss of life, will go down as one of the worst in modern history.

We need to understand what went wrong as quickly as possible as there are so many other similar buildings around the country. Residents of the tower are understandably furious with the Kensington and Chelsea Tenant Management Organisation – the body responsible for managing Grenfell Tower – that their warnings about the risk of fire were ignored. Complaints over recent months and years include access for fire engines being blocked, piles of rubbish being allowed to accumulate near exits and inexplicable power surges. This is clearly unacceptable and may have hampered the rescue effort but emerging evidence suggests the reason why this fire was so severe was down to the recent refurbishment to improve the thermal performance of the building.

Grenfell Tower was constructed in the 1970s. It features four storeys of community and office use at the base of the building with 20 storeys of flats above. Its construction is unremarkable; an insitu concrete core at the centre of the building containing concrete escape stair and lifts. The floors are insitu concrete with the flats arranged around the core. This is a straightforward and robust structural system that is widely used today.

The original cladding was precast spandrel panels at cill height with single-glazed aluminium windows above. The thermal performance of this type of facade is feeble, so the building has been upgraded using funding from the ECO programme, with a design by architect Studio E and Rydon as main contractor.

As part of this work, the building was upgraded with a new heating and cladding system. A company called Harley Facades did the cladding – the company says it provides a “comprehensive design and construction package for building envelopes”. It is worth noting Harley Facades was formed after Harley Curtain Wall – a company with the same director and almost identical logo as Harley Facades – went bust in September 2015 after design documentation had been approved by Kensington & Chelsea council but before works on the building had finished.

Drawings show the new facade consists of spandrel panels, with windows separated by panels in a nod to the original design. The windows are a tilt turn design made from polyester powder-coated aluminium. According to the drawings, a cassette type insulation system was used – the panels appear to feature an OSB or other timber backing board faced with Celotex FR5000 insulation board. An aluminium rainscreen has been used to protect the insulation from the weather and provide a decorative finish. This is separated from the insulation by a 50mm wide cavity.

A Reynobond ACM panel was specified for the rainscreen. ACM stands for aluminium composite materials and consists of a core faced with an aluminium sheet 0.5mm thick. The panel is available in two variants. The first features a polyethylene core; the other is said to be more fire resistant with a mineral core. The composite construction enables a rigid yet lightweight panel with the appearance of aluminium available in a choice of different colours while keeping costs down.

This is the reason why people are told to stay inside their flats - there is a presumption that the building construction will prevent the fire spreading

High-rise buildings are designed to contain a fire within the flat where it breaks out. Photographs of a severe fire, caused by a faulty tumble dryer, on the seventh floor of a flat in Shepherds Bush in August last year demonstrate that this works. This is the reason why people are told to stay inside their flats – there is a presumption that the building construction will prevent the fire spreading.

Many experts are suggesting the cladding used for the Grenfell Tower refurbishment contributed to the rapid spread of fire. Film footage shows flames shooting up the side of the building and sheets of flaming material raining down. The fire broke out on a warm night – it is likely windows were open with curtains blowing in the breeze, which would have contributed to the terrifying spread of fire throughout the building.

There have been several high-profile fires associated with this form of cladding. These include a fire at the Address Downtown hotel in Dubai on News Year’s Eve 2015, another at the Marina Torch tower also in Dubai earlier that year and the Lacrosse tower in Melbourne, also in 2015. In each case, fire spread rapidly up the side of the building with flaming material raining down on to the pavements below.

If a polyethylene-cored cladding panel was used at Grenfell Tower - and the contractor and manufacturer are reported to have confirmed this today - it is hardly surprising the fire spread so quickly. The panel’s aluminium facing is resistant to the surface spread of flame but this would be of little use where the intensity of the fire would quickly breach the thin aluminium facing, which has a relatively low melting point. Cavities in buildings can contribute to the spread of fire as these function like a chimney drawing flames upwards. And if cavity barriers inhibiting the spread of fire are missing or have gaps, fire can spread vertically internally up a building. This is a bit like suspending a plastic sheet in mid-air and lighting the bottom.

Of course, we do not yet know what caused the fire in Grenfell Tower and there is no suggestion that building regulations were infringed or the work was sub-standard. The building regulations say external walls should resist the spread of fire, not that they should be constructed from non-combustible materials.

As far back as 2000 a parliamentary committee said the guidance in Part B might not be adequate to prevent the external spread of fire

There have been many calls for Part B, the regulation dealing with fire safety, to be revised in response to the risks of external fire spread via the cladding. As far back as 2000 a parliamentary committee investigating a fatal fire at Garnock Court in Ayrshire in 1999 where fire spread externally via the cladding said the guidance in Part B might not be adequate to prevent the external spread of fire. It said external cladding systems should be required either to be entirely non-combustible, or to be proven through full-scale testing not to pose an unacceptable level of risk in terms of fire spread. It also said it should not take a serious fire in which many people are killed before all reasonable steps are taken towards minimising the risks. This advice was not incorporated into the 2010 revision of Part B. Since then there has been the Lakanal House fire where six people died. The coroner’s 2013 report into this disaster found problems with fire safety including the building’s fire resistance.

Instead the government has sat on its hands and Part B remains unrevised allowing the use of cladding systems such as the one used on Grenfell Tower. Leaving aside the potentially serious political repercussions for the Conservative government, the investigation into fire spread at Grenfell Tower needs to be swiftly concluded and the findings incorporated into fire regulations.


Readers' comments (45)

  • I'm a little confused by this statement - "The building regulations say external walls should resist the spread of fire, not that they should be constructed from non-combustible materials."

    For example, Approved Document B Volume 2 Paragraphs 12.5 to 12.9 provides recommendations for external walls which I doubt a polyethylene core panel could have met:

    12.5. The external envelope of a building should not provide a medium for fire spread if it is likely to be a risk to health or safety. The use of combustible materials in the cladding system and extensive cavities may present such a risk in tall buildings.
    External walls should either meet the guidance given in paragraphs 12.6 to 12.9 or meet the performance criteria given in the BRE Report Fire performance of external thermal insulation for walls of multi storey buildings (BR 135) for cladding systems using full scale test data from BS 8414-1:2002 or BS 8414-2:2005.

    12.7 In a building with a storey 18m or more above ground level any insulation product, filler material (not including gaskets, sealants and similar) etc. used in the external wall construction should be of limited combustibility (see Appendix A). This restriction does not apply to masonry cavity wall construction which complies with Diagram 34 in Section 9.

    Both Grenfell (and previously Lakanal House) were greater than 18m high. I would suggest “insulation product” would cover cladding panels also and again I very much doubt a product with a Polyethylene core can be considered to be limited combustibility (as per Table A7) nor would meet the recommendations of BR 135 and BS 8414-1:2002 or BS 8414-2:2005.

    I may have misinterpreted this but this the way I have always applied it on buildings I have worked upon.

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  • To confirm, "as per Table A7" refers to Table A7 in Approved Document B Volume 2.

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  • According to Reynobond's technical data sheet both versions of Reynobond have a Class 0 fire rating for surface spread of flame.

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  • Yes Class O in accordance with BS 476 Parts 6 and 7 testing and criteria. And I understand how an aluminium enclosed combustible core can achieve this.

    However, for buildings greater that 18m tall (and as referred to previously) the cladding/insulation materials should be of limited combustibility – Table A7 defines this as:

    a. Any non-combustible material listed in Table A6 (which doesn’t include polyethylene);
    b. Any material of density 300/kg/m’ or more, which when tested to BS 476-11:1982, does not flame and the rise in temperature on the furnace thermocouple is not more than 20ºC;
    c. Any material with a non-combustible core at least 8mm thick having combustible facings (on one or both sides) not more than 0.5mm thick. (Where a flame spread rating is specified, these materials must also meet the appropriate test requirements);
    d. Any material of density less than 300kg/m3, which when tested to BS 476-11:1982, does not flame for more than 10 seconds and the rise in temperature on the centre (specimen) thermocouple is not more than 35°C and on the furnace thermocouple is not more than 25ºC.

    Or, meet the requirements/criteria of thermal insulation for walls of multi storey buildings (BR 135) for cladding systems using full scale test data from BS 8414-1:2002 or BS 8414-2:2005. The testing criteria includes:

    a) extent of flame spread over the surface of the cladding system (both vertically and horizontally);
    b) extent of flame spread and damage within any intermediate layers (both vertically and horizontally);
    c) estimate of any flame spread and damage within the cavity, if present, (both vertically and horizontally);
    d) extent to which the external face of the cladding system has burnt away or become detached;
    e) details of any collapse or partial collapse of the cladding system.

    So for the use of this particular cladding to not contravene of Building Regulations requirements, I understand that the above standards would also need to have been met for this particular use (building more than 18m tall).

    I don’t see how a polyethylene core panel could have met these requirements. Also, does it not beg the question why the manufacturer/supplier would offer/produce a “less flammable” version if the standard Polyethylene product could suffice.

    The use of this particular cladding on this particular building is surely a question for whomever (multiple) specified, justified and approved the use of the product assuming it was considered as part of the Building Regulations application.

    Finally, although produced by manufacturers’ the following guidance is also useful to understand the requirements of guidance to the Building Regulations:

    Also a presentation:

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  • chris1608

    I can't help but feel the ACM manufacturers know enough to produce the diagram on page 3 of this document, yet continue to sell the non fire resistant product.

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  • Yes, agreed, but whether right or wrong, under the UK Building Regulations the polyethylene (flammable) version may be used in buildings less than 18m tall in the UK (and there will no doubt be other countries which will allow use of the polyethylene version).

    However, someone specified the polyethelene cladding should be used for Grenfell despite it apparently not being appropriate for the building (as it is greater than 18m in height) - so in this case it would not the fault of the manufacturer unless they convinced others that their product met all the required performance criteria. And even then there should have been due diligence undertaken by the design and build team and it would also be subject to Building Control approval...

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  • chris1608

    I would argue that the manufacturers know enough not to sell the flammable version as it is palpably not fit for purpose on any building. Perhaps the most apt lay-person's question in the immediate aftermath of this tragedy was "why would anyone clad a building in something flammable?" - and no, timber isn't the same as petrol. As architects are reliant on specialist designers, we are all reliant on manufacturers to exercise some judgment and fully declare the risks of their products. A fire tearing up a building on 'flash over' is unacceptable anywhere, at any time.

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  • There are multiple factors that seem inadequate or illogical to me within the building design of Grenville Tower and it's refurbishment and regarding fire escape strategies. Whether the Building Regulations have been met or not. Maintenance Issues: 1. The Dry Risers did not function & so the Fire Brigade could not connect to mains water at high level under pressure to fight the fire from inside the building. 2. No central fire alarm system appears to have been set off - from tenants reports. Was there a central fire alarm system hard wired throughout the building? Refurbishment & Retrofit Issues: 1. There was no sprinkler system. So far fire experts are saying this would have saved lives and reduced the spread of fire or extinguished it, at least inside the building. 2. Did all flats have 1 hour fire doors onto the escape route with adequate door closers? Did some tenants remove closers to the front doors to apartments? Because the question should be asked - how did the fire spread to the stairwell as it appears to have done? 3. There appears to have been no smoke extraction system within the stairwell - why not - especially as it was the only escape route? 4. The Cladding: Other comments here seem to suggest that the cladding system did not meet the Building Regulations Part B for buildings above 18m in height. Celotex claim that their insulation product smoulders but does not burn. In my experience this is not true. It will ignite at a high temperature. It burns with thick black toxic smoke. OSB (the assumed backing board) is compressed timber shavings or sawdust created into board using resin. Resin is flamable. OSB also has a petroleum based coating as a moisture barrier and therefore doubly presents a spread of flame risk. Aluminium - the assumed outer cladding does ignite and a relatively low temperatures for a metal - this was evidenced in the burning of ships bombed during the Falklands War. 5. Looking at footage of the flame spread it certainly looks as if fire stopping was absent in places although much of it was in place (from photos of the burned out panels this looks like a Rockwool type product such as Conlit). 6. The fire spread appears to have been driven by the prevailing wind - hence this plus other factors such as the chimney effect through the cavity - caused rapid spread of flame. 7. Aluminium burns and this must have ignited the window frames in some cases. 8. A new gas main was allegedly being fitted within the stairwell, which was also the only escape route. This is a potential fire hazard. Fire Escape Strategy Issues: 1. Is ONE escape route really sufficient in a multi-storey residential block with a high number of residents? I think the Building Regulations should be revised and a requirement for more than one escape route in relation to the number of people escaping and as an alternative way out of high buildings should be legislated for. 2. The 'stay-put' policy has always concerned me. I have never agreed with it unless in a hospital situation with intensive care patients who cannot be moved. In the event of a fire the building should be evacuated and muster points should be allocated in the surrounding area. This would also allow people to be accounted for. 3. There should be fire drills. Morgan Stanley successfully evacuated all of their staff plus visitors from the Twin Towers because they were well drilled and because staff escaped in pairs holding hands, so that no one was left behind. 4. Was there a fire warden system? This is not only a safety measure but it helps the community to take control of their own safety in an fire and would also help to ensure escape routes were kept clear of debris and rubbish. My points simply amount to saying that multiple factors need to be addressed to ensure the safety of all residential tower blocks. Certainly no combustible material or polystyrene based materials should be fitted to the exteriors - only materials that resist fire and prevent surface spread of flame. I also question the need for a cavity within external insulated cladding panels and this needs discussion vis a vis the need to account for dew point in an external situation.

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  • SomeoneStoleMyNick

    It isn't only about the cladding. It's primarily about how the building is planned.

    All you underpaid, inexperienced, stressed, commerical resi architects reading this: stop designing building with unventilated, artificially lit internal access corridors leading to a single escape stair buried deep in the middle of the plan with no smoke lobbies and no venting to the outside.


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  • Clichy

    @Toby McCorry, @ArchitectureScribble - excellent posts obviously written with knowledge. I share the concern that this specification was permitted; it seems obvious from the news videos that the cladding was the primary accelerant of the fire and the speed that it climbed the building was truly shocking. The speed of the flashover between panels was quite frightening.
    Obviously multiple parties involved in the specification, approval and construction of this cladding must have some hard questions to answer, if not actual prosecution.
    Equally the obviously inadequate ventilation in the common areas is of substantive concern - if, as alleged (I have not seen confirmation) the stairwell filled with smoke and there was a lack of lighting then that is criminal in every sense of the word.
    The wider issue of refurbishing blocks built to 1970s standards without bringing them up to current standards requires serious debate.

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