Insulation for metal workshop roof

[technium]

Hi

My workshop walls have now been lined as follows Shiplap - breatheable membrane - loft insulation - vapour barrier - 15mm mdf so now all thats left is the roof. The roof is painted metal with a felt type anti condensation layer on the underside but I want to insulate the roof so im thinking of putting loft insulation up then vapour barrier and hold it all up with thin ply or plasterboard to save on weight.

Does this sound ok or is there anything I need to think of of any better ideas?

thanks in advance

Colin

 

[mayo.mick]

What about using foilback "kingspan" insulation? I used this myself for my own workshop roof, 8'x4' 25mm sheets cut between the rafters. Comes in 50mm and 100mm too. Bit pricey but worth it. Cut snug between the rafters and it holds itself, odd screw underneath here and there. Very very light too.

 

[technium]

I have the odd bit of kingspan but was asking about loft insulation because I still have 3 rolls left over from insulating the walls so wouldnt be wasting money already spent if that makes sense?