I am renovating a house and have to remove retrofit insulation from the cavity as there is damp. I am, also, upgrading the wall ties so was thinking I could put PIR in the cavity and since I want to clad with brick slips or render could put some external wall insulation (either EPS or PIR) on in order to achieve the required U value. What I don’t understand is why some PIR boards are not identified as for cavity or external use when their descriptions are the same, other than a difference in price. Would standard PIR boards be okay to use for the applications I have stated if I use membranes between each layer e.g. over brickwork then over external insulation before cladding?