83. Areas are often excavated outside the foundation walls of buildings to give light or access to the basement, and require to be surrounded by a wall to retain the bank and present a neat appearance.

Such walls should be built of stone, as a stone wall offers greater resistance, when the mortar is green, to sliding on the bed joints than a brick wall.

In making the excavation the bank should be disturbed as little as possible, and in filling against the wall the soil should be deposited in layers and well tamped, and not dumped carelessly behind the wall. The filling should also be delayed until the mortar has had time to harden, or else the wall should be well braced.

Area walls are commonly built in the same manner as foundation walls and of a uniform thickness, generally about 20 inches for a depth of 7 feet. If more than 7 feet in height the wall should have a batter on the area side and should be increased in thickness at the bottom, so that the average thickness of the wall will be at least one-third of the height, unless the wall is braced by arches, buttresses or cross walls.

Area walls sustaining a street or alley should be made thicker than those in an open lot.

When an area wall is more than 10 feet long it is generally practicable to brace it from the basement wall by arches thrown across from one wall to the other, as shown in Fig. 45. When this cannot be done the wall should be stiffened by buttresses about every 10 feet.