The house foundation is the structure below that you pay the least attention to. It sits quietly below grade doing what it is supposed to do and that is anchoring your house to the ground. When the house foundation begins to fail then that is the time that you may notice the following:
- Cracks on the stucco or exterior wall finishing
- Separated block or brick joints
- Windows or doors misaligned
- Floor sagging or sloping
- Cracks on the basement wall
- Cracks on the flooring
These are small problems compared to structures built on sites with unstable soil and incorrect filling materials. Bigger problems can result in buckled walls which could definitely mean "danger! Your house is about to collapse!" heaved slabs and worst, the movement of the whole foundation system itself. Even an inch of movement or uneven settling of a house foundation could post danger to a person's life, safety and property, not to mention money.
What is a foundation? Foundation is the structure that transfers load to the underlying materials that could be soil, rock or even seabed. The foundation holds a structure up so it won't sink to the ground. The foundation also holds the structure down to keep it from being lifted or blown away by the elements. The foundation of your house must also be able water-resistant to a point, must be able to resists fungus and insect infestation, natural gases and of course the pressure of the soil that the house stands on. Without a sound foundation, your house could literally sink to the ground or blown away.
Building a new house is not an easy DIY-er task. For one, you need to get an architect for the building plans and permit. The architect will provide you with the necessary floor plans and construction drawings that include foundation and footing designs. You may wonder how the architect came up with the design but don't be. Architects and engineers are well-versed on computing live and dead loads and soil pressure and capacity. If you just want to add a new room or a deck to your house, then here are some of the basics about house foundation to give you an overview.
There are different foundation systems that you can choose for your house. It is therefore necessary that you know the condition of your soil. Is your soil clay, gravel, sand or silt? The best soil to build is on sand or gravel as there would be no need to add piles. However, if you are building a multi-level structure it is best to have your soil analyzed for load capacity. It is also important to consider the water level on your property and if the lot stand on bedrock below the surface or soft soil and debris?
If you are just going to do extension work on your house, it is best to familiarize yourself with the existing condition if your original house foundation. Is the foundation stable and shows no sign of moisture and movement? What's the material used? Note how high the water table on your lot is too.
Types of Foundation
There are two major types of foundations: shallow and deep. Shallow foundations refer to foundations that are about 1 meter deep. Deep foundations are embedded on the soil for building high rise buildings. There is also the seismic isolation foundation used to make a building earthquake proof to a degree. Shallow foundations are best for simple building and house construction. Here are the basic and most commonly used concrete foundations used in small scale structures.
- T-shape foundation or spread footing foundation is a form of isolated footing where each post is poured on top of a footing foundation placed below the frost line. A wall footing slightly wider than the intended wall is then poured to connect each post or column foundation. This system connects each and every column and foundation wall thereby rendering the foundation system very stable. After pouring the column and wall foundations, the walls are added and then finally the floor slab. This would require reinforcements in the form of steel bars.
- Slab on grade foundation as the name implies is a single layer of concrete from minimum of 150mm (6 inches) up to 200mm-250mm in thickness. The slab is poured thicker at the sides or edges to form a fundamental footing with reinforcing bars. The poured slab should be poured on top of several inches of gravel. It is customary for the slab to be poured on a mold set in the ground leaving no space between the ground and the structure. This type of foundation is best used in warmer climates where there is no frost or thaw line to consider. This type of foundation is cheap but sturdy and may even be less susceptible to termite infestation as there are no spaces or any material leading from the ground to the main structure.
The main disadvantage of this type of foundation is the low elevation that exposes the building to flood damage and possible heat loss.
- Mat Foundation is where the concrete slab is of the same dimension of the structure so the weight of the building is evenly distributed on the mat. This type of foundation can either be constructed near the ground or at the lowest part of the basement. When used in high rise building, the mat foundation can be several meters high with heavy steel reinforcements.
There are other forms of foundations but the outlying principle is basically the same. The only difference is the type of material used. The foundation has to be poured concrete but posts can be made of wood or metal. Remember to add waterproofing chemicals to your concrete used for foundations and footings. Do not skimp on foundations as they are the very core of your structure.