Yes, you can insulate a mobile home after repairing roof leaks. Insulating a mobile home roof is a job for a professional. An excellent reference book for weatherizing a mobile home is called "Your Mobile Home: Energy and Repair Guide for Manufactured Housing" published by Saturn Resource Management. Before insulating a mobile home, the contractor will have to fix all of the leaks in the roof. Secondly, the water-damaged materials in the roof (e.g. old insulation, dry wall, rotten plywood, etc.) should be removed. Remove any visible mold from the wood and make certain that all of the building components are dry. When all of these steps are complete, the roof can be insulated. The U.S. Department of Energy has more information about insulating your mobile home.
