Fig. 38.
Double Damp-Proof Course and Hollow Wall.
a, a—Damp-proof courses. b—Level of neighbouring ground. c—Floor-boards. d—Floor joist. f—Vertical space in wall. g—Concrete under foundation and over site of house.
This suffices when there is no basement. If there is a basement an open area around the house is desirable. Where for a given wall this cannot be secured, the vertical damp-proof course already described must be made to extend from the foundations well above the ground level. The open area, however, should be insisted on whenever practicable. The damp-proof course protects the walls from damp proceeding from the soil around or beneath the house.
It is necessary also that the walls above the level of the ground should, as far as possible, be kept free from damp. Damp walls, not due to ascent of moisture, may be caused by
(1) Rain falling on window-sills which do not project beyond the walls, and consequently do not throw the water clear of them. This is remedied by constructing the window-sills so as to project beyond the walls, and “throating” them to prevent rain from running along the bottom of the sill. The throat is shown at a, Fig. 39.
(2) Rain falling on cornices and other projecting portions of the wall itself. The evil from this source may be diminished by sloping the top of the projection, downwards from the face of the wall.
(3) Parapet walls, gables, etc., not being properly covered with coping. All such walls should be topped with a projecting slab of stone, or with a damp-proof course under the top course of bricks, which should be laid on edge.
(4) Overflow from defective roof-gutters or rain-water pipes. In this case, either clearing out, repairing, or renewing is required.
(5) Rain beating against the walls. This as a rule produces no great harm, if the walls are well constructed. Most of the water runs off as it falls on the surface. It is advisable, however, to protect a much exposed wall by a coating of Portland cement, or in extreme cases with slate. Various impervious paints have also been employed.
