Grenfell Tower contractors appeared more concerned about "cost and delay" than fire safety, the inquiry heard into the disaster heard as campaigners marked 1,000 days since the fire.
During discussions about installing cavity barriers designed to stop flames in March 2015, it was noted that upgrading from the minimum required standard of 30 minutes' fire-resistance to 120 minutes' would cost an extra £12,000, the inquiry heard on Tuesday.
In an email chain between external wall subcontractor Harley Facades, lead contractor Rydon and architects Studio E, Rydon contracts manager Simon Lawrence writes: "Harley via their supply chain are questioning the rating of the cladding firebreaks.
"Apparently by going to 2hrs as we discussed has a cost increase of around £12k."
Studio E design lead Neil Crawford agreed with the inquiry's chief lawyer Richard Millett QC that there was pressure on-site to avoid having to recommend the upgraded cavity barriers.
Mr Millett asked him: "And the main concern was cost and delay as opposed to fire safety?".
Mr Crawford, who led the architects' design team but is not a registered architect, replied: "I can't speak on behalf of the other participants in that conversation but you might read that into what they've written, yes."
An expert report in 2018 found there were "missing and defective cavity barriers" in the final refurbishment and that horizontal cavity barriers had been incorrectly installed vertically.
The report by Dr Barbara Lane, commissioned by the inquiry, also found windows in individual flats had no fire barriers encasing them and these openings were surrounded by combustible material.
"The assembly - taken together with the insulation material on the existing external wall, the missing and defective cavity barriers - became part of a successful combustion process", she wrote.
A total of 72 people died in the June 2017 fire at the west London tower block.