Report comment

I'm a little confused by this statement - "The building regulations say external walls should resist the spread of fire, not that they should be constructed from non-combustible materials."

For example, Approved Document B Volume 2 Paragraphs 12.5 to 12.9 provides recommendations for external walls which I doubt a polyethylene core panel could have met:

12.5. The external envelope of a building should not provide a medium for fire spread if it is likely to be a risk to health or safety. The use of combustible materials in the cladding system and extensive cavities may present such a risk in tall buildings.
External walls should either meet the guidance given in paragraphs 12.6 to 12.9 or meet the performance criteria given in the BRE Report Fire performance of external thermal insulation for walls of multi storey buildings (BR 135) for cladding systems using full scale test data from BS 8414-1:2002 or BS 8414-2:2005.

12.7 In a building with a storey 18m or more above ground level any insulation product, filler material (not including gaskets, sealants and similar) etc. used in the external wall construction should be of limited combustibility (see Appendix A). This restriction does not apply to masonry cavity wall construction which complies with Diagram 34 in Section 9.

Both Grenfell (and previously Lakanal House) were greater than 18m high. I would suggest “insulation product” would cover cladding panels also and again I very much doubt a product with a Polyethylene core can be considered to be limited combustibility (as per Table A7) nor would meet the recommendations of BR 135 and BS 8414-1:2002 or BS 8414-2:2005.

I may have misinterpreted this but this the way I have always applied it on buildings I have worked upon.