This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
108. It is often found necessary to excavate areas outside the foundation walls of a building. These serve to light the building in some cases, and in others to give access to the basement. In order to keep the bank of earth from caving in, and to present a neat appearance on the inside, they require a surrounding wall. Stone walls, when the joints are wet, offer greater resistance to sliding on the bed than brick walls; hence, area walls are usually built of stone.
109. When excavations are made for area walls, the bank ought to be disturbed as little as possible, and when the soil is thrown back behind the wall, it should not be dumped carelessly, but deposited in layers, and well tamped. No filling should be done until the mortar in the wall has had time to harden; or if the filling has to be done at once, the wall should be well braced.
110. Areas are usually built in the same manner as stone or brick foundation walls; that is, they are laid up in cement mortar, and have a thickness of 20 inches for a stone wall to a depth of 7 feet, and 16 inches for a brick wall to the same depth.
When an area wall exceeds 7 feet in depth, there should be a batter on the area side, as shown in Fig. 41, and it should be increased in thickness at the bottom, so that the average thickness will be one-fourth the height, unless the wall is braced by arches, buttresses, or cross-walls.
When an area wall is 10 feet long, bracing arches can usually be thrown from one wall to another, as shown in Fig. 42. Here a shows the area wall; b, the concrete bottom of the area itself; c, the bracing arch, shown in this case as a segmental arch made of three courses of brick; d, the brick filling on top of the arch; and c, the area coping.