Describes the results of a major study to find out whether or not wall insulation installed without a vapour barrier causes an increased risk of moisture damage within walls. The exterior walls of 96 homes in Portland, Oregon were opened. Presents results of field and laboratory tests which show the absence of indications of moisture damage. Gives data on shrinkage and settling of insulation and results of air leakage measurements by fan pressurization tests. Concludes that the addition of wallinsulation without a vapour barrier does not cause moisture damage in existing homes.