The thickness of foundation walls in all large cities is controlled by law, and in general will require that walls to a depth of ten or twelve feet below the ground shall be four inches thicker than the wall above, for brick, and eight inches for stone, with an increase of four inches for every ten feet below this. In clay, which is more seriously affected by frost than gravel, it is a good plan to build foundations with a batter on the outside of six to twelve inches, as in Fig. 103, so that any movement of the earth will readily free itself from the wall, which should be made smooth on the outside with cement. Areas and Vaults. Areas are often required, to give light or access to basements, and these will need a retaining wall to keep back the earth. Stone should be used for areas of any size, and, in excavating, the bank should be disturbed as little as possible and refilled carefully. If the area is not more than six or seven feet deep, a good wall of a uniform thickness of twenty inches will be sufficient but, if deeper, the wall should be made wider at the bottom and battered. If the wall is more than ten feet long, cross walls or arches should be built to connect with the main building. The bottom of the area should be carried at least six inches below the sill of window or door, and covered with stone flagging or brick laid in cement, with a small brick cesspool and cover, connected with the main drain.

Fig. 103. Wall with Hatter.

Fig. 103. Wall with Hatter.

The space under the sidewalks and entrance steps or porches is often utilized for coal or general storage purposes. This requires a wall at the street line which shall be heavy enough to sustain the pressure of the street and the weight of the sidewalk. If it is possible to divide this space so that the partition walls can be run back to the main building about every ten feet, the construction can be simplified, but if an open space is required, a very heavy wall must be built at the street line, and steel beams laid from this wall to the building which will buttress the top of the street wall and support the weight of the sidewalk as well. Brick arches may be turned between these beams and leveled up for the sidewalk, or a concrete or flagstone sidewalk may be constructed over them. (Fig. 104.) If brick arches are turned, to be covered with an ordinary brick paving, the top of the arch should be coated with hot asphalt. Any of the modern forms of fireproof floor construction may be used for the sidewalk covering, finished with concrete or "granolithic" surface.

Dampness

As a protection against dampness, the outside of all cellar and vault walls in wet situations, should be coated with hot asphalt or Portland cement. Asphalt, applied while boiling hot in two or more coats from top to bottom, is considered the most lasting, if the ground is very damp, as Portland cement is affected by frost and is easily cracked by settlement of the walls, while asphalt, having considerable elasticity, remains sound and tight. Coal tar is sometimes used, but will gradually become brittle and crumble away.