anyone insulated a conservatory roof?

[robinbanks]

Where did I say to add timber? I'm suggesting you prove to yourself whether adding the insulation makes it a usable room by literally just fixing insulation using fixings 5mm longer than the thickness of the board, and large washers. Put it up, live with it a few months, if it works out, decorate it. If it doesn't, take it down and use the insulation elsewhere and the only marks left behind are 3 holes in each rafter. You don't need to put a hundred kilos of timber, plasterboard and plaster up there to prove the concept