When constructing an extension, you may need to dig the foundation deeper than existing foundations to meet current building codes. Concrete slabs are typically 6 inches thick, but they can also be 4 to 8 inches thick for mobile homes, garages, workshops, driveways and patios. The footings must be inspected before the rest of the foundation can be poured, and the entire foundation is inspected before construction. Constructing a foundation with a basement is more complex and expensive than a standard base, as concrete walls will be added to define separate rooms.
Block foundations cost more than poured foundations due to the skilled labor required to lay the blocks, but they are also at risk of leakage through all joints between blocks and mortar. The final cost of your concrete foundation depends on the size and type you install, as well as the prices for labor and materials in your area. This range is due to many factors, including the size and type of foundation, the type of problem and the fact that the house needs to be lifted from the foundation during replacement. The installation involves pouring a concrete slab, the walls of the foundation (stem) and the footings (concrete platforms), which extend to the ground under the walls.
The total cost of laying a concrete foundation will include more than just labor costs and material costs. If your house uses a concrete crawl space base, the concrete footings that support the walls of the access space are poured and installed by the linear foot. Although many different factors will affect the total cost of laying a concrete foundation for a new house or building, square footage of space is one of the largest. Prefabricated foundations are used for sheds or garages, but they are not strong enough for a house foundation. Usually, a concrete pour starts with a soil test to determine the best concrete mix for the job and how much excavation you will need.
Local building codes may prohibit foundations from being built with concrete blocks and instead require you to use concrete blocks.