Hi, I've just bought a 150 ish year old end of terrace cottage, near Sheffield UK, with a single story extension, (100 ish years old), which used to be a stable on the end of the building and was converted to living quarters in the 80's. The extension is on the north facing side of the house. This extension has solid walls that are two bricks thick & no cavity. There is then battening that has plaster board fastened to it. The battening is of different thickness on different walls which leaves a 'cavity' between the brick and plaster board of different depths, from 2 to 8 inches. The original house is built of stone with rubble filled walls. The extension is noticeably colder than the rest of the house and this is where my living room is! I'm thinking that I'd like to insulate the walls of my living room from the inside because it's empty at the moment and I'll be decorating it anyway. I'd planned to remove the plaster board, make the battening deeper in places and fill between the cavity with some kind of insulation. I'd then re plaster board and skim over with a thin layer of plaster. After doing some research, I've read that I need to be wary of condensation and that my house construction probably needs to be permeable so it can breathe. Can anyone give me advise on what type of insulation I can use and if my method sounds sensible Many thanks... Mick.