Many new homes are supported on poured concrete foundation walls. DSCN0023A poured concrete foundation wall is actually made up of two pourings, the first is a footing, which is wider than the final wall and is designed to create a level surface upon which to put the finished foundation wall. This is not dissimilar to the footings on a block or rock foundation wall.
In engineering there are two types of load, a "point-load" which is a load that is localized to a specific location, even though it is usually really not applied at a sharp point and a distributed load, which is spread across a large area.
The reason for the footings being wider than the finished wall is to convert the point-load of the wall and everything it supports to a distributed load which is spread across a wider surface area. This reduces the likelihood of point-load settlement caused by the physical weight of the wall bearing down on soil.
To explain the principal of point-load versus distributed load better, take a piece of wood and lie it flat on a stable surface, place a nail upside down on the wood, and using a smaller length of wood as a hammer, hit the nail as hard as you can, taking care not to have hit yourself with the wood. The nail drives itself into the piece you are using as a hammer, not the other way round.
This is because, like the weight of a foundation wall and house on the footings, the weight, or in this case the force of the blow, is spread across the head of the nail, through the shank of the nail, onto the wood below.
Similarly the weight of the house is spread across the footings through the foundation wall, onto the ground below. The footings, usually do not sink because they are engineered to evenly spread the load of the house. See more about foundations and their problems here: [ Ссылка ]
