Damp and ground-air may not only rise through the floor of a house; they may find entrance through the basement walls. It is of little use covering the-site with an impervious layer of asphalt if the walls be left pervious and in contact with the ground. Hence the necessity either of surrounding the base-ment with an open area. or of building the walls of such materials and in such a manner as to prevent the ingress of moisture and air.

Many an old house nestling into a hillside has nothing to protect its back wall from damp but a trench full of rubble stones with a stone drain at the bottom. For a time such a rubble-trench may be of service, but it is sure to choke at last, and then it ceases to be any protection.

Undoubtedly an open area, sufficiently wide to admit of easy cleansing, and tending to a depth of about 6 inches below the damp-course under the basement floor, is an effectual preventative of ground-air and ground-damp in walls. The bottom of the area should be formed of concrete, with asphalt similar to that on the ground-layer and walls; if good natural asphalt with a gritted surface is used, no further covering is required. This arrangement is illustrated in Fig. 18, page 56. In very wet ground it will be advantageous to continue the asphalt layer through the area wall and up the back of it as shown in the figure; the house will then stand in a dry waterproof dam.

Where space for an open area cannot be afforded, a dry area, or "air-drain" (as it is sometimes termed), may be formed with sloping flags, or with an additional wall of brick or stone. Fig 22 illustrates a bad example of a base-ment surrounded by a dry area formed with flags; the window sill and the sloping ground conduct the rain-water to the upper edge of the flagging and so into the wall and area; there is no dampcourse to the wall, and the floor is formed of flags without any underlying bed of concrete or layer of asphalt.

Fig. 22  Bad Example of stone Wall and Dry Area. A, stone foundation; b, flags forming area: C, flag forming door.

Fig. 22 -Bad Example of stone Wall and Dry Area. A, stone foundation; b, flags forming area: C, flag forming door.

Fig 23   Dry Area formed with Brick work.

Fig 23 - Dry Area formed with Brick work.

A, concrete foundation and ground-layer; B lower asphalt damp-course; c, upper asphalt damp-course. D. stone coping over area; E, concrete floor-Surface; F. tile border on cement mortar.

Of course a dry area may be constructed of stone without the defects depicted in the last figure, but it is a better plan to form the area by means of an additional thin wall of brick or stone, the wall and area being covered at the surface of the ground with weathered stone, concrete, or bricks, which must be jointed and pointed with cement-mortar so as to prevent the ingress of surface-water. Examples of dry areas formed with an additional brick wall are shown in figs. 23 and 24. The wider the area is made the better; two horizontal damp-eourscs should be laid in the wall, as at B and c. Small openings for ventilating the area should be provided at intervals, as shown at E E in Fig. 24.

Closely akin to a dry area is a hollow wall. In this the air-space or cavity is formed within the main wall itself and not outside it as in the previous case. The arrangement is illustrated in

Fig. 24   Dry Are formed with Brick Wall and Arch.

Fig. 24 - Dry Are formed with Brick Wall and Arch.

C, upper asphalt damp-conn: D, brick arch over area; E.E, ventilating-shaft from area Fig. 25, but it cannot be recommended, as part of the wall is left unprotected, and in very wet ground the water will penetrate to the cavity and soak into the inner lining of brickwork.

Neither the hollow wall nor the dry area is a satisfactory method of construction. In each there is a narrow cavity, well-nigh impossible of access to the householder, but capable of hurl touring vermin and facilitating their movements, and while both are of some use in retarding the ingress of ordinary damp, they assist rather than impede the entrance of ground-air and water. Where an open area of sufficient width cannot be formed, the most sanitary construction is a solid wall, rendered impervious alike to moisture and to air.

As most bricks and stones are very far from being impervious, it follows that a wall built of these materials alone - however well it may be constructed - cannot be absolutely water-proof. Certainly a wall built of good bricks in Portland-cement mortar (one part of cement to two of sand) and well grouted with neat cement, ought to be practically impervious, especially if a cavity (which need not be more than \ inch or | inch wide) be left in the body of the wall and run with grout; but such is the carelessness of the ordinary bricklayer that it is almost certain it will not be. A coat of Portland-cement mortar (1 cement+1 sand) carefully applied to the exterior of the wall after the joints have been well raked out, is a safer protection than the grouted cavity.

A method sometime- adopted is to build a vertical layer of rooflng-slates between two skins of brickwork, but the process is tedious and expensive.

A better method is to form a narrow cavity, inch or inch wide, in the l>ody of the wall, and run it full every two or three courses, with molten asphalt or waterproof composition. Great care must be taken that the cavity is kept free from mortar, etc.; this can best be done by means of a thin board built into the wall to form the cavity and lifted out every two or three courses, when the cavity can l>e at once filled with asphalt. In building walls of this kind, it is better that the mortar in the brickwork should not extend quite up to the cavity, in order that the composition can key into the joints, as shown in Fig. 26. For convenience in filling the cavity, one skin of the brickwork is often carried one course higher than the other, and a piece of sheet-iron resting on wedge-shaped chairs is placed on the lower brickwork as shown in the figure. Or a spouted utensil may be used for pouring the liquid. The cavity must be quite free from water when the molten composition is run in.