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Grenfell: ‘Aspirational’ U-value led to combustible insulation

15 July 2020

An “aspirational” target to keep heat loss from Grenfell Tower to a minimum resulted in the selection of the combustible Celotex RS5000 insulation for the building, the Grenfell Tower Inquiry has heard.

The Inquiry yesterday heard evidence from Studio E architect Bruce Sounes. Sounes confirmed that engineer Max Fordham had proposed a U-value of 0.15 w/m2K for the building.

It examined emails from Sounes to employees at Max Fordham, in which the architect said he had sent off enquiries to Rockwool and Kingspan on insulation options for the building. In one email dated 5 July 2012, Sounes said: “The 0.15 U-value you’ve asked for looks to me a bit aspirational”. He also attached a spreadsheet to the email containing his analysis of the thickness of the Rockwool required to reach the suggested U-value, which indicated that more than 450mm of insulation would be needed.

In response, an employee at Max Fordham said: “Those thicknesses of Rockwool seem a bit high – does that also include the thermal bridging from fastenings/frame etc and a ventilated cavity? For a glass fibre slab (excluding fastenings etc) we’d expect to be able to achieve 0.15 U-value with approx 180 mm (material only).”

The Max Fordham employee went on: “A phenolic foam insulation would give greater insulation for the depth. Hopefully the response from Kingspan may be closer to target.”

Sounes made further enquiries to Rockwool but in the end decided to “pass” on a glass wool product because of concerns about buildability and aesthetics.

He added that after the exchange of emails: “I did not pursue any other alternatives because it would appear the thermal conductivity of the foam products, Rockwool or any other fibre, couldn’t compete with.”

‘Exceptional’ sustainability record

Asked by Inquiry chair Sir Martin Moore-Bick if Sounes thought simply about abandoning the target of a 0.15 U-value in favour of a more relaxed target, Sounes said: “We’ve done a lot of work with Max Fordham and they pride themselves as an aspirational engineer and we’ve gone with them. When I say gone with them, we’ve participated in numerous designs where they have done exceptionally sustainable buildings.”

Counsel to the Inquiry Kate Grange QC then turned to an August 2012 email from an employee at Max Fordham, which recommended the Celotex FR5000 product as insulation for the building. The email read: “The Celotex FR5000 is a solid PIR board, data sheet attached, I think this is the only type of product that will give us the required performance.”

Asked what his reaction to the suitability of Celotex FR5000 for use in the overcladding system was, Sounes said he could not recall but that it did not prompt any concerns. “I think, going back, PIR and phenolic had become all but standard in every project at this time,” he added. He also confirmed that Studio E had no reason to think FR5000 was not compliant with Building Regulations or the guidance in Approved Document B thanks to its class 0 fire performance.

Sir Martin-Moore Bick then asked: “What I’m really interested to know is this: you obviously knew about these boards, from what you have told us, and I suspect that you knew that they were quite efficient. Your first instinct, on the other hand, was to reach for the Rockwool. Why was that?”

Sounes replied: “It’s the safest. This was a time when BREEAM assessments would only give Rockwool category A status, so maximum points could only be achieved with Rockwool. When I started as a young architect, that’s what we all used.”

Grange asked Sounes: “Did you have any awareness, once the Rockwool fell out of the picture, that what you were looking at with other products was less safe from a fire performance point of view? Did you have any awareness of that at the time?”

Sounes said: “I would have to agree that you can’t put them side by side and say the mineral wool isn’t less likely to burn. Obviously, it’s not going to burn. But at the time I was of the view, which I think I’ve said, that the Celotex didn’ t burn, it just charred. The whole history of polyurethanes had been solved and it was safe to use in cavities. That was my understanding at the time.”

The inquiry continues.