When a sump pump is installed in the crawlspace at the lowest point, a hole 20 x 20 x 20 inches is excavated to accommodate a piece of 12x12-inch flue liner. The sump pump is placed in the flue liner with guy wires from the pump to the floor joist. Moisture Vapor On Outside Wall, Floors, And Ceilings Moisture vapor migrates from one area of a house to another. This is caused by different temperatures on each side of a wall, floor, or ceiling, which in turn produce vapor pressure. The vapor, unless prevented by vapor retarders or barriers, can move through floors, walls, and ceilings.
Vapor barriers prevent moisture vapor from moving from one area to another.
Barriers are needed on insulation to prevent moisture vapor from penetrating. If moisture vapor is allowed to penetrate the insulation, it becomes wet and ceases to be an insulator. Aluminum foil is totally resistant to vapor passage while craft paper is highly resistant but not totally resistant. Polyethylene plastic also is used as a vapor barrier material. Window Condensation Condensation in cold weather is reduced or eliminated by installing storm windows on existing windows.