Studio E should never have specified the insulation that was used in the Grenfell Tower refurbishment project, the inquiry has been told.

The practice’s confidence in Celotex RS5000 was “an ongoing major failure on their part” to understand Building Regulations, expert witness Paul Hyett said yesterday.

A “reasonably competent architect” should have known PIR (polyisocyanurate) insulation was not compliant with Approved Document B (ADB) of the Building Regulations, he added.

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