To keep the environment within the house satisfactorily dry requires doing more than what is commonly thought of as waterproofing- the sealing out of liquid water. Many of the common irritations of home ownership are caused by the entrance of water in the form of vapor. Troubles caused by dampness can be minimized if not eliminated that encloses the concrete slab and the walls below grade. The material used for the envelope is commonly referred to as a membrane and it is thicker and more effective than the commonly used polyethylene sheeting. The membrane must be placed on the prepared grade and continued vertically up the outside of the foundation wall to the height of the floor so that the floor is isolated. Roofing felts were probably the first moisture barriers used below concrete slabs. The popular polyethylene film is low in cost and easily installed but it is easily punctured. Butly rubber sheeting is a good moisture barrier that is rugged and long lasting but is expensive and must be prefabricated for the job. Prefabricated panels of asphalt or asphalt-plastic have the lowest perm ratings. Asphalt membrane one-eighth an inch thick is also available in roles.