We are renovating an add on building which is used as a bathroom, it is built of concrete blocks. Having stripped out the old plaster board we found 80mm thick polystyrene panels used for insulation. I want to replace these, but thinking of using panels of only 40mm thick, so as to keep the room as big as possible. Will using thinner panels make a huge difference to the insulation, or am I worrying about nothing.
Any advice or comments would be most welcome.