The cavity extend vertically all along the height of the wall, except at the openings, where it is discontinued. The cavity should terminate near coping in case of flat roods with parapet walls and up-to or near eaves level in case of sloping roof. In the foundations, the cavity should start near the ground level or 150 mm below the D.P.C level.
A cavity wall or hollow wall consists of two separate walls called leaves or skins with a cavity or gap in between. The cavity wall construction is an effective method of damp prevention, in which the main wall of building is shielded by an outer skin wall, leaving a cavity between the two. The cavity wall are often constructed for giving better insulation to the building. It also prevents the dampness to enter and acts as sound insulation.