Architect Bruce Sounes told the inquiry yesterday (14 July) that he had originally wanted to use the non-combustible Rockwool insulation on the recladding of the tower in west London.
However, to meet the U-value target of 0.15W/m²K for the insulation put forward as a target by engineers Max Fordham, the architects believed so much Rockwool would have been needed it would have created ’buildability and aesthetic issues’.
According to Sounes, who said he had done his own ’amateur detective’ calculations to work out the amounts required, the requisite thickness of Rockwool would have pushed the cladding line out to around an ‘unfeasible’ 450mm.
Emails show that the architects was aiming instead at a specification of between 150mm and 200mm for the part of the cavity in which the insulation would sit.
Counsel for the inquiry Kate Grange showed an email from Andrew McQuatt of Max Fordham, who suggested that Celotex RS5000 insulation could be used to meet the U-value target, which actually exceeded the requirement for refurbishment projects and was the standard for new-build homes – to fit the space specified.
Grange had previously grilled Sounes over why the architect had stuck to the ambitious U-value target, given that he had admitted that his first choice material of rock wool would have been ’the safest in terms of fire’.
Sounes said he ’couldn’t see any reason to abandon the target’, telling the inquiry ‘it was in the project’s interests to try and achieve it.’
He said: ’With hindsight, obviously no one challenged the insulation.’
Sounes added: ’We have done a lot of work with Max Fordham and they pride themselves as aspirational engineers […] they have done exceptionally sustainable buildings.
’The emphasis on passive sustainability was something we shared with Max Fordham over a number of years.’
Counsel questioned Sounes’s claims that 450mm of Rockwool would have been needed to achieve the 0.15W/m²K U-value targeted and pointed to evidence supplied to the inquiry by its architectural expert Paul Hyett.
She said: ’Mr Hyett has run the calculations to see what thickness of mineral wool could be achieved and what U-value you would get. His calculations are that, with a mineral wool, it ’s possible for the spandrel condition to produce a 0.14W/m²K U-value, so that’ s under the 0.15W/m²K, against a 250mm mineral wool insulation build-up. So it’s perhaps thicker than you were envisaging in your email of 200mm, but it’s 250mm.’
Sounes replied that his thickness calculations had been based on an online calculator on manufacturer Rockwool’s website.
Asked about Max Fordham’s suggestion of using Celotex, a PIR board, insulation Sounes said he did not have concerns saying ’these type of products were widely used’.
He said: ’At the time, I was of the view that Celotex didn’t burn it just charred and it was safe to use in cavities.’
The inquiry continues.
Counsel Kate Grange: ’What was your reaction when you received this email about the suitability of the Celotex FR5000 product for use in the overcladding system?
Bruce Sounes: ’I can’ t recall’
Counsel: ’Did you have any concerns about the reference to PIR board in this email? Did that ring any alarm bells for you?’
Sounes: ’No. I think , going back, PIR and phenolic had become all but standard in every project at this time.’
Counsel: ’When you say standard for every project , can you be clear what you mean? Every project you had worked on?’
Sounes: ’Every project that I had worked on. There were exceptions, but invariably some form of foam board was used in the façades and on the roof .
Counsel: ’I think we clarified at the very beginning of your evidence you hadn’t done a residential overcladding above 18 metres before; is that correct? ’
Counsel: ’So these other projects were low-rise projects?’