Thanks for the heads-up. There is internal lime plaster on one side of the building, however there is cement external render. Would this keep the wall airtight? I don't care about meeting any targets or building regs. I just want a warmer home and I am sure any future purchaser would be happy there is some insulation in such an old property. It will be me fitting the wall insulation, I just want to make sure I achieve a decent improvement and it not be a waste of money.