I'm so sorry not to have thanked Chippe999 for his helpful advice - I'd lost the bookmark! I still haven't done the job, so the advice is just as valid now as it was then. Thanks!
I have a large are of flat roofed accommodation (dining room 22m2, kitchen 14m2 and Utility room 9m2). The existing insulation over all the flat roof area appears to be 1â€
