Dampness in buildings is caused by moisture entering through walls, floors, and roofs. It can be from ground moisture rising up, rain splashing on exterior walls, or condensation of atmospheric moisture on interior surfaces. Damp proofing treatments include applying damp proof courses of hot bitumen, mastic asphalt, or plastic sheeting to foundations, walls and floors. Membrane waterproofing of roofs uses layers of asphalt or plastic sheets applied with hot bitumen to prevent leakage. Proper drainage systems and slope of roofs are also important to prevent dampness.