An architect who drew up the specifications for the Grenfell Tower refurbishment has said he was not involved in any discussion about the fire performance of the proposed cladding panels, and that instead the focus was on “appearance and cost”.

Tomas Rek told the public inquiry into the disaster that the client and the cladding contractor were motivated by cost concerns to switch to the type of panels that would become the main cause of the fire’s rapid spread.

The Czech-trained architect said he had never previously worked with aluminium composite panels, did not know that cladding panels could be made with combustible plastic cores, and was not trained in using facade materials in overcladding systems.

Rek was the fourth member of staff from the architecture firm Studio E to give evidence at the inquiry. He was asked by Richard Millett QC, counsel to the inquiry, how the original plans for zinc panels came to be dropped and combustible aluminium composite panels selected in their place.

Millett asked: “Did you get the impression that Studio E was under pressure from the client to specify cheaper ACM material rather than zinc.”

Rek replied: “From the client. Yes.”

The client on the project was the Kensington and Chelsea Tenant Management Organisation, and the building was owned by the Royal Borough of Kensington and Chelsea (RBKC). RBKC’s planners were involved in discussions about appearance.

The inquiry was shown an email to Rek from Mark Harris of Harley Facades, the cladding subcontractor, in which Harris said: “From a Harley selfish point of view our preference would be to use ACM.” This was because it could be confident about how much it would cost.

The public inquiry has already concluded that the £10m refurbishment of Grenfell Tower breached building regulations prohibiting the use of certain combinations of combustible materials on high-rise residential towers.

Rek said despite drawing up a specification, he did not check buildings regulations guidance about fire resistance and fire spread on external walls.

“I do not recall discussing the fire rating or fire performance of polyethylene-based composite panels while I worked on the project,” he said. “I also do not recall discussing whether these panels came with fire-retardant cores or whether any investigation on compliance with part B of the Building Regulations 2010 had taken place.”

Asked if it would have been important to familiarise himself with building regulations guidance on fire before he drafted the specification for the cladding, he replied: “Retrospectively, it would have helped if I had a better understanding. It’s a lesson learned. But we had a fire consultant on the job and I considered fire-related issues quite a complicated subject outside of my competence.”

The choices of materials were made despite the standardised specification document that Rek issued including a warning that “systemised building envelopes” must meet building regulations and that “aluminium envelope systems do not normally have significant resistance to fire”.

The document also said that the use of any combustible material for the insulation might need to be considered as the building height increased. Grenfell was fitted with combustible insulation panels that helped spread the fire.

Millett asked Rek if he was aware of that as a general principle at the time of his involvement in the Grenfell Tower project. He replied: “No.”

Was he aware of the concept of materials of limited combustibility, he was asked. He replied: “I’m not sure.”

Was it right to say he was not aware of what would constitute a material of limited combustibility? “Correct,” he replied.

The Grenfell Tower fire on 14 June 2017 claimed 72 lives. The inquiry continues.