Preparing to build your home: choosing a footing

Footings are the below-ground "feet" of a building, with the two most common being concrete slabs or strip footings. These guidelines will help you learn about the different kinds of footings and decide which foundation is best for your home.

Whatever type of house you are planning, consider pouring a concrete slab as a base. It is a comparatively low cost operation and yields a prepared base for tiles, carpet or vinyl. As well, there will be no termites or rotting floors; you will have the bonus of insulation by the earth itself.

To ensure that surface runoff cannot enter the house, slabs are slightly raised above ground level, and given all-around drainage. In flood-prone areas, however, slabs are not usually a good idea.

Strip footings — usually of reinforced concrete — are placed in narrow trenches in the soil, to support just the walls of the building. In the past, footings of stone were commonly used, but these have little tensile strength, so that if there is any tendency for the house to bend or settle with moisture changes in the soil, the footings — and therefore the building — may crack.

Stone is a solid, traditional footing material but because of its weight has to be cut into relatively small blocks before it can be used. By their very nature, stone footings have little tensile strength, and any bending or swelling in the soil will cause flexing of the structure, which in most forms of building other than wood will result in cracks. Brick has the same problem, though their size makes them easier to work with.

Concrete is an ideal material for strip footings as the depth, width and reinforcing can be fairly well predicted and precisely engineered to suit various foundation conditions. It is also easy to work with when compared with the hard labour of manoeuvring heavy blocks of stone or bricks into a hole.

Pier (or pile) and beam footings are a solution to the problem of not being able to find a stable bearing for a building near the surface. An engineer is required to design a system of regularly spaced piers, holes for which are bored into the ground until a sound bearing is found. These are combined with beams that are deep and narrow, to provide a bridge over the unstable surface layers of earth.

Such construction is variable in cost, as the depth of the piers may be unknown, unless extensive preliminary drilling is carried out, which is not normally an option in domestic building. The cost is due to the boring of the piers, the pouring of extra quantities of concrete both in piers and beams, the reinforcing required, and the need for engineering advice.The alternative may be to use a building method that is lighter, and not so dependent on very stable footings, such as pole-frame construction.