90. These features, although not strictly a part of the foundations, are intimately connected with them, and are generally included in the same contract.

The thickness and bracing of area walls has already been considered (see Section 83). The materials and workmanship of the walls should be the same as in the foundation walls.

Window areas intended for light and ventilation should be of ample size, so as not to obstruct the light more than possible.

For small cellar windows sunk not more than 2 feet below the grade line, a semicircular area with a 9-inch brick wall will give the greatest durability for the least cost. If the area is 3 or 4 feet deep, and as many in length and width, the thickness of the wall should not be less than 12 inches for brick and 18 inches for stone.

Area walls should be coped with stone flagging, set in cement, the edge of the flagging projecting 1 inch over the face of the wall. If flagging cannot be obtained without excessive expense the top of the wall should be covered with 1 to 1 Portland cement mortar, about inch thick. Freestones and all porous stones are unsuited for area or fence copings.

Drainage. - The bottom of the area should be carried at least 6 inches below the window sill and should be formed of stone flagging or of brick laid in cement. Beneath the bottom of the area a small cesspool or sand-trap (say 8 inches square) should be built, which should be connected by a 3-inch drain pipe with the main drain. A cast iron strainer or drain plate should be set over the cesspool, flush with or a little below the paving, so that it can be readily removed and the cesspool cleaned. The footings of the area walls should be started as deep as the bottom of the cesspool, both being below the frost line.

Window And Entrance Areas 10050

Fig. 49.

91. Entrance Areas

All area steps, when practicable, should be of stone, or of stone and brick combined. When the soil is hard and compact and not subject to heaving by frost, a small set of steps may be economically built by shaping the earth to the rake of the steps and building the steps directly on the earth, laying two courses of brick, in cement, for the risers, and covering with 2-inch stone treads, as shown in Fig. 49. All parts of the steps should be set in cement, and well pointed, and the ends of the treads should be built into the side walls. If the area is 6 feet or more in depth, or if the soil is sandy or a wet clay, then the area must be excavated beneath the steps and entirely surrounded by a wall. The steps may be formed of 2-inch stone risers and treads, or of solid stone, the ends in either case being supported by the side walls. If of solid stone the front of each step should rest on the back of the stone below it, as shown at At Fig. 50. If built of treads and risers they may be arranged either as shown at B or C. The arrangement shown at B is the strongest.

91 Entrance Areas 10051

Fig. 50.

If the steps are more than 5 feet long a bearing wall or iron string should be built under the middle of the steps.

Stone steps should always be pitched forward about 1/8 of an inch in the width of the tread.

In many localities plank steps, supported on plank strings, will last for a long time if the ground is excavated below them and the area walled up all around, and when they decay it is a small matter to replace them.

The platform at the bottom of the steps should be of stone or brick, set at least 4 inches below the sill of the door giving entrance to the building, and should be provided with cesspool, plate and drain, as described in Section 90.

All outside stone steps, fence coping, etc., should be set on a foundation carried at least 2 feet below grade, and in localities affected by frost below the freezing line.

92. Vaults are often built under entrance steps and porches, the walls of the vault forming the foundation for the steps and platform. The roof of the vault is generally formed of a brick arch or vault, two rowlocks in thickness, with the stone steps set in cement mortar on top of the arch.

Vaults under sidewalks may either be arched over with brick, the top of the arch leveled off with sand, cinders or concrete, and the sidewalk laid thereon, or the sidewalk itself, if of large stone flags, may be made to form the roof of the vault. In the latter case the joints of the stone slabs are closely fitted and often rebated, then caulked with oakum to within about 2 inches of the top and the remaining space filled with hot asphalt or asphaltic mastic. This will make a tight job for a time, but in the course of two or three years the joints will need to be cleaned out and refilled.

Any form of fireproof floor construction may also be used for covering sidewalk vaults and a cement sidewalk finished on top of it. This probably makes the best walk and the most durable construction, with a comparative slight thickness.

In San Francisco it is very common to build the sidewalks of cement, with steel tension bars or cables imbedded in the bottom, so that the same construction answers both for the walk and for covering the vault.

If brick arches, covered with sand, and a stone or brick pavement are used, the top of the arch should be coated with hot asphalt.