Q: I have an older modular home [25 yrs old]. I am planning to drywall all the outside walls and I would like to know if I should put a vapour barrier over the existing paneling before I apply the dry wall, thinking this would help in sealing and improving insulation of the walls from outside drafts or would this become a moisture problem. The existing walls are rated [R10] batt insulation, vapour barrier and paneling.
A: To add extra insulation consider applying 1 inch rigid shiplap edge polyurethane foam insulation (such as Dow Styrofoam Wall Mate or equivalent) over the existing walls and then go over top with the 1/2" drywall. No vapour barrier is required. You will require electrical box extensions (switches & duplex receptacles) to compensate for the additional wall thickness. These are available at most Building Supply stores. You can add ceiling crown mouldings and baseboards to give it a finished look.