I wonder if someone could help me please;
Im planning on installing rigid board insulation (e.g celotex/kingspan) on the inside of my house (its a 1920s bungalow with thin 15cm timber frame walls). Would you mind advising on the following?
1. I assume I can just leave the existing walls and plaster completely alone and just build an internal stud wall which I can fill with insulation. If so do I just attach the new studs to the existing studs through the plaster(using some very long screws/nails?) or do I need to remove all the old plaster to reveal the existing studs?
2. Do I need to leave an air gap on either side of the celotex/kingpspan, or should it be flush against the plasterboard?
3. Do I need to put some form of water proof barrier between the celotex/kingspan and the plasterboard, and if so which side (I think its the internal side right?)
4. If I wish to install 100mm of celotex what would be the total size of the new stud wall (i.e how much of the room would I loose?)
Thanks very much!