Grenfell: Architect’s confidence in Celotex insulation ‘a major failure’

Paul Hyett

Architect Studio E’s confidence in the combustible Celotex polyisocyanurate insulation specified to be used behind the ACM rainscreen cladding panels during the refurbishment of Grenfell Tower represented a “major failure”, the Grenfell Tower Inquiry has heard.

Expert witness Paul Hyett, a former president of the Royal Institute of British Architects (RIBA) and a former principal of HKS Architects, was giving evidence to the Inquiry for a second day, having produced a report for the Inquiry.

In his report, Hyett said: “It [Celotex 5000] did not meet any of the definitions for materials of limited combustibility as set out in Table A7 of Approved Document B2. Studio E should not have specified an insulation product that did not carry proper certification as evidence of its suitability in meeting the guidelines of ADB2 and the requirements of the Building Regulations.”

He added: “Studio E’s continued confidence in the Celotex RS5000 product, and the use of PIR insulation within the cladding system, represents an ongoing major failure on their part to understand both the requirements of the Building Regulations and the guidance given within ADB2 with respect to insulation in external walls. That failure of understanding appears to have extended to both [cladding subcontractor] Harley (Mr Daniel Anketell-Jones) and, surprisingly , [fire consultant] Exova (Mr Ashton)."

Hyett agreed with lead counsel to the Inquiry Richard Millett QC that combustible materials could be incorporated into a rainscreen system in accordance with Approved Document B if the total wall construction underwent a full-scale BS8414 system test and the results met the BR 135 performance criteria, or if a fire engineering approach set out in the Building Control Alliance (BCA) Technical Guidance Note 18 involving either a desktop study or a holistic fire engineering solution was carried out.

But he also agreed that if none of those three alternatives were adopted as the route to compliance, then the use of PIR or phenolic insulation was “essentially prohibited” by ADB2.

He confirmed that this meant Studio E should have satisfied itself that the Celotex FR5000, RS5000 and the Kingspan Kooltherm K15 used on the building were materials of limited combustibility.

Millett asked: “And from a prudent architect’s point of view, would the prudent architect, if asking someone like Exova or Harley or Rydon, have expected them to have done the same?”

Hyett replied: “Yes.”

Expert ‘astonished’ by fire consultant’s advice

Millett went on to ask Hyett about an extract from an email exchange in September 2014 between Neil Crawford of Studio E and Terry Ashton of Exova. Exova was not retained after main contractor Rydon was appointed in 2014 but continued to give advice on the project. In his report, Hyett noted an answer given by Ashton to a question from Crawford, in which Ashton said: “If the insulation in the cavities behind the rainscreen cladding is combustible you will need to provide cavity barrier as shown on your drawing.”

Hyett said in his report: “Mr Ashton’s reply is astonishing, coming from an alleged expert in fire safety within construction. By stating: ‘If the insulation … is combustible’ he appears to be condoning an outright breach of ADB2 guidance under paragraph 12.7.’

Millett asked: “Now, just looking at that , do you agree that if another route to compliance with the Building Regulations had been adopted, in other words one other than the linear route to compliance under paragraphs 12.6 to 12.9, then incorporation of an insulation which was combustible may not have been a breach of the Building Regulations?"

Hyett replied: “Yes.”

Millett asked: “So is it possible, then, for cladding systems as a whole to satisfy the B4 requirement by other routes even though they included combustible products?”

Hyett replied: “I believe that’s correct.”

Millett asked: “Now, if Mr Ashton didn’t know, let’s assume as a fact at the moment he didn’t know what route to compliance had been adopted, do you take the view that his response might have been reasonable?”

Hyett replied that he did not believe this. He went on: “Anybody giving advice like this should understand the context in which the advice is being given. They should get the information in front of them. He should have already known that the building was over 18 metres high. If he didn’t, he should have got the information in front of him. If he had forgotten, he should have reminded himself. Unqualified advice is just not acceptable. This is very, very serious territory here. He should have established the facts and then given the advice. Having established the facts, I think he should have been astonished.”

Turning to ask Hyett about Crawford, Millett asked that if Crawford knew that none of the three alternative routes to compliance was being considered, it would have been reasonable for him to have relied on Ashton’s statement as providing “any kind of comfort to him that he could go ahead and use combustible insulation”.

Hyett replied: “He shouldn’t have accepted such advice. He should have raised questions.”

Millett asked: “When you say ‘shouldn’t have’, are you saying that his accepting the advice and not raising questions fell below the standard of the reasonably competent architect?”

Hyett replied: “Yes, yes, yes.”

ACM cladding

Hyett said he wouldn’t have expected a reasonably competent architect to have known that ACM panels of the type used on the Grenfell Tower refurbishment (Reynobond PE 55) were at the time manufactured with different cores – a polyethylene core and an ‘FR’ (“fire resistant”) core.

However, he said he would have expected an architect preparing to work on the project to have obtained such knowledge. He also confirmed that he would have expected a reasonably competent architect to be aware of the fire performance properties of ACM panels in general.

But Hyett accepted that it was industry practice that ACM was “commonly prescribed” at the time, and that this would bear on the standard a reasonably competent architect should be judged when the prescribed it.

Hyett said: “I think we’re comfortable to specify products which are regularly used. One gains increasing comfort in that way. But there is still the obligation to check that that product meets the requirements of ADB2, and it’s specific within that document as to what the performance should be. So I think a degree of comfort can be obtained or enjoyed by the architect, but, at the end of the day, they’ve got to be satisfied that the particular manufacturer and particular product is okay.”

Inquiry chair Sir Martin Moore-Bick asked Hyett if ACM readily supported combustion.

Hyett replied: “No. I think it’s difficult to get it to burn, but once it’s burning, it burns with ferocity.” And he confirmed that it would add significantly to the fire load of the building once burning.

Sir Martin Moore-Bick went on to ask if this was something architects were generally aware of at the time.

Hyett replied: “We weren’t.”

The ‘pros and cons’ of design and build

In a section of his report discussing the “pros and cons” of design and build contracts, Hyett noted: “Under traditional procurement the architect has far greater control for selecting and specifying the buildings materials and components. Under design and build, the architect usually shows indicative arrangements which may frequently be less developed at tender stage. He may frequently be asked to obtain tenders on a variety of options – for example cladding – as occurred at Grenfell Tower. Indeed, even after appointment the successful builder may introduce major changes to the specification during design development and value engineering.”

Millett asked Hyett if it was his opinion that whatever major changes are made to the specification by the contractor during design development and value engineering, a reasonably competent architect would see it as their responsibility to confirm compliance of the materials which are specified with the Building Regulations.

Hyett replied: “Yes. Of course it depends on the point at which the project is put out to tender, it depends on whether the architect is novated and transfers…responsibility effectively is retained. But essentially the answer is yes.”

Millett asked: “So unless he is specifically instructed, you say that the architect’s obligation to confirm compliance of the material specified with the Building Regulations remains undiminished?”

Hyett replied: “If the architect is retained, that is correct.”


Millett went on to ask Hyett if he agreed that the design and builder taking the project on (Studio E was novated to Rydon after it was awarded the contract) would “have a really thorough check themselves”, but that this wouldn’t “absolve” the architect from having done its previous check to satisfy itself that the materials and products it was specifying in the NBS specification were compliant with the Building Regulations.

Hyett replied: “The issue of checking is I’m sure going to come up a lot, and I think there’s checking upon checking with this job, and I don’t like too much checking. What I like is the correct process of analysis at the right time by the right people. The contractor I don’t think is necessarily competent to carry out the check, although some contractors employ their own architects. I don’t think we should assume that they carry out the check. What they should be doing is satisfying themselves that the work has been thoroughly checked, and that would take the form of: ‘You guys are coming on board as our architects. What processes have you been through? Let’s look at some of the issues that have been developed along the way. We have the following questions from the point at which we were preparing our tender. We’ll bring them all to the table because we won the job. Here we go’.”

He added that a competent architect “needs to be checking their work at every single stage as they go through”.

When it came to subcontractors, Hyett said in his report: “It is also my opinion that any obligation on the part of the subcontractor to ‘complete the design in accordance with the designated code of practice’ does not impose an obligation upon that subcontractor to undertake a checking role or to assume responsibility for any or all past work of the architect. Further this most certainly does not exonerate the architect for any design failures in its own past work that are not ’picked-up’ by the subcontractor.”

But Hyett added: “I don’t want to imply with this that a subcontractor has no responsibilities for their own work, and it’s important here to remember that Harley had offered themselves, through their own documentation, as experts in overcladding buildings… And I don’t think a subcontractor can just say, ‘Well, we breezed up, we’ve got no responsibility even to comment on anything, we’ll take it all blind.’ You would expect them to have some substantial knowledge which they would inform their work with, and they would raise questions if they thought something was fundamentally wrong.”

The Inquiry continues.

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