Marie-Louise writes from London, Ontario: "We would like to re-insulate our house and the way we want to do is to leave the old drywall in place and set up a new frame out of 2*4 that we will then fill in with insulation and install a vapour barrier before we put new drywall on it. We realise it will make the rooms a bit smaller but I am more worried about if that is a proper way or if it could lead to moisture/mold problems. There is no vapour barrier installed so the house has brick on the outside with some insulation in the walls (but not much)."

Answer: As long as the existing insulation does not have a vapor retarder on the warm side it is acceptable to build out the wall with 2x4s as described. You can then insulate the new framing with FIBERGLAS™ insulation, making sure the vapor retarder is on the warm side of the assembly. The vapor retarder should be continuous. You can then install drywall.