Foundation Fundamentals

The foundation of a house has a very important job.  It is responsible for connecting the house to the ground below and taking the weight off of the house and putting it onto the soil and rock beneath it.  It does all this preferably with little to no movement or settlement of the soil immediately underneath the house.

If a lot of movement occurs in the underlying soil, the foundation and the home itself can be badly damaged.  House foundations that are shallow are more prone to movement from seasonal conditions such as drastic temperature changes, rainfall and drought or freeze/thaw cycles.   

Cooler environments require foundations to be poured deeper down under the ground in order to stay safely away from any soil with water in it that may have the potential to cause heaving of the house.  Deep house foundations are not usually affected by these changes in the environment because they are outside the ‘zone of influence’.

Foundations are made from various materials.  Material selection is based on the area’s climate.  There are foundations built out of stone, brick or pre-treated lumber; most often though, house foundations are constructed out of concrete.  In areas that are particularly wet, such as on the coast, houses are commonly built up on posts.

There are three major types of house foundations.  They are concrete slab, crawl space and basement. Basement foundations are deep foundations.  Pier and beam foundations have a crawl space underneath with concrete footings and piers that support the floor joints and wood beams of the home.  The most common type of house foundation is the concrete slab.

The concrete slab foundation is an example of a shallow house foundation is also called ‘slab-on-grade’ foundation.  This type of foundation actually moves up and down with the soil and rock underneath it as it shrinks and heaves with moisture changes.  Houses built with this type of foundation don’t have basements but can be built quickly and are very economical.

Concrete slab foundation is most likely the simplest kind to build.  It takes a minimal amount of labor, formwork and site preparation to produce.  Slab concrete works best in warm climates and on sites that are level. Slabs tend to develop issues when utilized further north due to the freezing grounds in the winter, which can cause the concrete slab to shift and also makes for cold floors.  

A concrete slab-on-grade foundation consists of a smooth concrete pad that is poured directly on the ground and is about 4 to 6 inches thick.  There is wire mesh and embedded inside the concrete. Underneath the concrete is a layer of gravel that is also 4 to 6 inches thick. Between the two layers is a 4 millimeter sheet of plastic that functions as a moisture barrier.  

The perimeter of the concrete slab forms beams that extend down about 2 feet deep.  This deeper set concrete around the edge of the slab holds the slab in place. Inside the base of the beams are steel reinforcing bars for extra support.

Many times a lot of the electrical conduit for a house must be laid in place prior to the pouring of the concrete slab.  Sewer pipes are in fact embedded within the slab.

No matter what kind of foundation your house has, it is important to take good care of it.  Make sure your foundation remains safe and sound by performing regular checks for cracks, bulges or other warning signs of shifting and settling.