Safetyman, I would you consider how often you are carrying out hot works. i.e. is it a one off. If it is a one off you could consider Viroc (not cheap) or similar and purchase enough sheets to carry out tasks. If it is on a regular basis then you should consider a more permenant system such as over cladding or removable screens. I speak to a local insulation company as they deal with a range of products for cladding steel beams etc. The roofs are more complex. I clad a welding shop entirely using double lapped boards and one hour jointing compound to walls, ceilings and roof. Obviously hot works were day in day out and the building was steel frame. This was the guidance from the local fire officer. Really is worth speaking to your local insulation company or fire officer as theres a good chance they have come up against this situation previously. Theres a good chance theres better products of a lighter weight since I carried out this work as it was about 15 years ago. regards