Walls are not subjected to standing water, and the water-resistant membranes used as house wraps are designed to be porous enough to let moisture escape. Walls also have vapor barriers or air barriers. Damp proofing is another aspect of waterproofing. Masonry walls are built with a damp-proof course to prevent rising damp, and the concrete in foundations needs to be damp-proofed or waterproofed with a liquid coating.