The contract for the foundations, all concreting, construction of walls, floors, roof, and all plastering, should be given to a mason builder on the same "quantity basis." The foundations are the most important part of any building, and should be the most substantial. The object of the foundation is to distribute the weight of the structure evenly over the area upon which it stands and thus avoid likelihood of vertical settlements. For this reason the higher the building is to be, the wider and deeper the supports or footings for the foundation must be. If soft or yielding ground is encountered piling should be resorted to in order to carry the weight of the building on a more solid basis.
Footings may be of iron, timber, large flat building stones laid directly on the ground or in a bed of concrete, or they may be concrete alone or concrete and stepped-up brickwork. For ordinary purposes good concrete, from one to two feet in thickness, laid in simple trenches dug in firm earth with the sides extending six inches beyond the lines of the foundation wall will answer. These footings should be a foot or two in thickness and sunk below the frost line four or five feet to prevent upheavals from extreme frost.
Footing courses built on slopes, especially clay slopes, are always liable to slide, and should be formed in steps of as long sections as possible, great care being exercised to secure a perfect bond at the stepping places.
Where the foundation walls rest partly on solid rock and partly on artificial footings great care should be taken to make all footings equally firm with the rock so as to prevent unequal sagging.
It is often found that compressible soils, even alluvium and soft clay, will bear from one to two tons per square foot with but little settlement, yet under a steady load a uniform settlement will occur. It is often cheaper therefore to employ spread footings over a large area than it is to drive piles. These spread footings may be built either of concrete reinforced with tension rods or with I beams or old railroad iron imbedded in concrete as a base. Spread footings are thicker than ordinary footings and taper inward from the bottom as they ascend. If the ground be spongy or bad it may be necessary to drive piles in addition, in which case an engineer should be consulted.
All footings should be properly proportioned to the weight they are designed to carry, whether continuous as in a foundation wall or isolated as when divided into piers. The pressure on the soil per square foot should be equal where the soil is uniform, and if the soil be uneven in its bearing power the footings should be proportioned to the weight properly distributed to insure uniform settlement.
The foundation walls above the footing courses are usually stone, brick or concrete. The thickness of the foundation wall is usually controlled by building laws. For a twelve-inch wall, stone or brick foundation walls should be not less than sixteen inches thick. If the walls of the building are to be of twelve-inch hollow tile as recommended here, a twelve-inch concrete foundation wall will be sufficient, as the concrete will be denser in its composition than the building tile and therefore sufficient for sustaining the lighter walls above.
Unless there is plenty of cheap building stone in the vicinity a concrete foundation wall laid in temporary wood forms will be the cheapest kind. The footings for such a wall will not require any forms, but may be formed by raw concrete dumped into smoothly dug trenches.
An allowance is made by custom in wall measurement for doors, windows and other openings. This rule varies in different localities, being in some communities one-half and in others one-third of the covered area.