Certificate for Celotex insulation in tower block said it should only be used with non-combustible cladding

Building safety experts warned in 2014 that the insulation planned for use on Grenfell Tower – which was installed and which fuelled the fatal fire in June – should be used only with non-combustible cladding.

The Guardian has seen a formal certificate issued by the building inspectors’ organisation, Local Authority Building Control, stating that the insulation chosen for the £10m tower refit was acceptable for use on tall buildings only if used with fibre cement panels, which do not burn..

But on Grenfell Tower, combustible polyethylene filled panels were installed on top of synthetic insulation. The insulation, known as Celotex RS5000, was made from polyisocyanurate, which burns when exposed to heat and gives off toxic cyanide fumes.

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It emerged on Wednesday that Luana Gomes, 12, who survived the tower inferno in north Kensington, London, on 14 June, suffered cyanide poisoning, although fumes from burning furniture and other household items might also have been to blame.

The experts’ certificate will increase concern over why the Royal Borough of Kensington and Chelsea’s building control team certified the building work on Grenfell Tower as complying “with the relevant provisions”. There were 16 site visits by council building inspectors from August 2014 to July 2016.

Photographs of the construction process seen by the Guardian give a clear view of the materials being used for the cladding system.

The manufacturer of the insulation Celotex also made clear that the fire performance report related to the specific components used in the test. It said: “Any changes to those components or to the construction methods used will need to be considered by the building designer.”



It has also emerged that a second combustible insulation material was used. Kingspan said one of its products was used “as part of a combination for which it was not designed and which Kingspan would never recommend”.



It said the material, a phenolic insulation called Kooltherm, had never been tested with polyethylene core aluminium panels and that the company “would be very surprised if such a system … would ever pass the appropriate British Standard 8414 large-scale test”. According to Kooltherm’s LABC certificate, phenolic products “do not meet the limited combustibility requirements” of building regulations guidance.

A spokesman for Kensington and Chelsea said: “We know there are many questions relating to fire safety standards.” The council declined to comment further “until this issue has been discussed with the police and the solicitors to the public inquiry once they have been appointed”.

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The certificate is one of a series produced by LABC, a membership organisation for all building control departments in England and Wales. The certificates are developed by a system of peer review and are routinely used by building control officers to help them determine whether proposed systems meet building regulations.

The certificate does not mean that building regulations can never be met using Celotex RS5000, but makes clear that testing to British Standard had been done in combination with specific non-combustible products.

Police have said they are investigating possible manslaughter as well as any “breaches of legislation and regulations”. Detectives are examining how the fire started and the speed of its spread, looking in particular at the cladding and insulation.

Since the fire, the Celotex insulation and the Reynobond PE aluminium cladding have been withdrawn from sale. Both products, which were used on Grenfell Tower, were considerably cheaper than the non-combustible alternatives, according to industry sources.

Celotex is said to be 30% to 50% cheaper than non-combustible mineral fibre insulation. Non-combustible cement-based cladding of the type used in the fire test with Celotex is described as about twice the price of the polyethylene-filled Reynobond aluminium panels that were eventually used on Grenfell.

Cost pressures on the Grenfell refurbishment appear to have been intense. It emerged last month that the project team specified a cheaper cladding, saving £293,368, after the Kensington and Chelsea Tenant Management Organisation suggested in an email the need for “good costs for Cllr Fielding Mellen [the council’s former deputy leader]”.

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Asked to comment on the LABC certificate, a spokesman for Kensington and Chelsea said: “The council is committed to cooperating fully with both the public inquiry and the criminal investigation. We do not think it is right to disclose documents or make comments relevant to the inquiry or subject to the investigation until this issue has been discussed with the police and the solicitors to the public inquiry once they have been appointed. The council does not want to prejudice the fair conduct of the public inquiry in any way.”

Meanwhile, two more NHS trusts in England have failed cladding fire safety tests, bringing the total to five. Newcastle upon Tyne hospitals NHS foundation trust found a small part of the Freeman hospital and a small part of the Royal Victoria infirmary to be of concern.

A building of the University College London Hospitals NHS foundation trust also failed the test following submission of a sample taken from the National Hospital for Neurology and Neurosurgery site.

The first two schools to have their building cladding tested also failed checks. Bridge primary school, in Islington, London, and London Enterprise academy, in Whitechapel, London, were found to have aluminium composite material cladding which did not pass combustibility tests. They were subsequently checked by the fire and rescue service and declared safe for continued use, according to the Department for Education.