Hi all. We moved into this property a few years back. The master bedroom is situated on the side of the house over a carport which leads to the garage behind. The room has always been cold during the winter which I expected. A couple of years ago I pulled the ceiling of the carport down and filled it with about 300mm cellotex insulation which has helped. Anyway its still cold and a mate of mine installs Air con/ heaters so we had one installed yesterday. When the fitter cut into the plsaterboard to run the pipes through he found a void of about 600mm up to a single skin (external) wall with no insulation in it, which would explaint the temperature in there... I imagine the whole room is like it and am considering fixing the whole problem, what are your suggestions as to the best method of insulating it going forward. Many thanks.
Photo of what was found when we cut through the plasterboard. The brick at the back is the external skin. https://ibb.co/cNVswWG
Simplest would be to add a layer of insulated plasterboard over your existing wall; you will lose quite a lot of internal space though. Alternatively add a layer of PIR behind the existing plasterboard. If you can, cut a suitable hole and fit it all from behind. If not it’s pull off the plasterboard and replace once you’ve insulated. You could also add a layer onto the inside of the external wall. Some U value calcs will give you an idea of the relative merits of each.