Materials used cost less and are energy efficient

It is agreed across the construction industry that PIR insulation has excellent energy efficiency performance. It is also cheaper per square metre than non-combustible products such as stone wool.

The products with top-of-the-range fire rating can achieve the same thermal performance as PIR, industry insiders say, but only if more panels are used.

That means buying more of the product and more space being required to home the insulation, potentially increasing building costs.

The roof of the V&A Dundee contains two forms of PIR insulation, both of which are manufactured by Kingspan and are rated as Euroclass E for fire safety. The company did not respond to a request for comment.

It is covered in a Sarnafil roofing membrane, which is attached to a steel deck. The membrane is also rated Euroclass E. Asked about the rating, a Sarnafil spokesman said: “Yes that is correct but that is when Sarnafil is burnt on its own, an application it never ever gets used in.

“This is a fire test within EN 13956: 2012. Sarnafil is an external roof waterproofing system that is installed on to a structural substrate and it is the fire testing of this ‘in use’ application, which should be considered above all.

“When tested to the relevant standards BS476 Part 3 and EN135011187 Broof t4 Sarnafil roof systems will meet the ‘Low Vulnerability’ requirements of the Scottish Building Regulations.”

The Euroclass system determines a product’s fire performance by measuring characteristics including ignitability, flame spread, heat release and smoke production.

The classifications run from the top rated A1, which is the only ‘noncombustible’ rating, to F.

Anything of B rating or below is deemed ‘combustible’.