Foundations for a single-story building strip will normally be 450 mm wide and at least 200 mm deep, while foundations for two-story buildings will be 600 mm wide and 200 mm deep. The depth of the foundation depends on how much weight you expect to put on it.
The minimum depth required for a strong foundation is based on the load it must support and the location within the building where the load is applied. If the building is made out of wood, then the foundation should be at least as deep as the floor frame. For steel or concrete buildings, the foundation should be at least as deep as the lowest floor level. The deeper the better because then any damage that occurs due to water entering the basement can be repaired easily when it arises.
Loads are divided into three categories: bearing, momentary, and permanent. A bearing load is one that forces objects together or against each other; an example is a load on a house caused by wind. A momentary load is one that causes objects to rotate around a point; examples include loads on a house caused by people or vehicles moving through its path. A permanent load is one that causes objects to deform over time; examples include a load on a house caused by its being above ground or not.
Basements are subjected to bearing and permanent loads.
In general, a slab thickness of 6 inches (150 mm) is recommended for residential and commercial structures, with reinforcing elements as per design. The methods for determining slab thickness varied depending on the kind of slab. Concrete used to make slabs is usually delivered in cubic yards or loads and mixed at the site before it is poured. A common mistake is to use too much or too little concrete when pouring a slab. If it is found after curing that the slab is more than 8 inches (200 mm) thick, then additional reinforcing is needed. Thicker slabs are easier to cast in one piece and require less cement per square foot.
The average thickness of a reinforced concrete floor is 10-12 inches (250-300 mm), but this will vary depending on the type of building work being done. For example, a floor in a warehouse might be half that thickness while a floor in a house could be 20 inches (500 mm) or more. Thick floors are easier to clean and maintain and can support more weight than thin floors. They are also better protected from damage caused by trucks driving over them.
Concrete has the ability to heal small cracks that appear during construction and other damage over time, but larger gaps should be filled or else your floor will become vulnerable to moisture damage.
A foundation wall with seven rows of blocks should be 24 inches wide and 12 inches deep, with a footing 30 inches below grade. Remember to provide a flat footing for the cinder block. This can be done by using broken glass, concrete, wood scraps, or any other material that provides traction for your feet while staying out of the soil. Be sure to keep your footing free of weeds and grass to help it hold water away from the wall.
The depth of your footings will depend on what kind of floor you build over them. If you are going with tile or stone, they usually need to be deeper than if you were going with carpet or hardwood. That being said, try not to go under your house more than 2 feet deep unless you have tile or stone underneath.
The goal here is to create enough room for water to drain away from the foundation wall. If you don't, you may be forced to spend money on additional plumbing upgrades later on.
Also make sure that you leave enough space above the footings for any ductwork or piping that might run through them. Ducting and piping can cause problems if it isn't allowed to move freely up and down as well as side-to-side. Any moving parts inside your home is also a problem because they are likely to break sooner rather than later.
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