I'm starting to think about how we can better insulate the existing parts of our house. They're solid brick walls and external insulation is not an option as we don't want to cover up the existing brickwork, so internal wall insulation it is.   The external walls, whilst originally plastered using lime have been at some point skimmed with gypsum and show no signs of damp, so moisture is not currently a problem - externally it's still pointed in lime mortar. The internal plaster build u