Concrete slab foundations are more common in northern states, where the soil is more susceptible to freezing during winter and can cause slab cracking. There are several good reasons for purchasing or constructing a home on a slab including lower cost and less risk of structural damage in some cases. Slab foundations have been in use since at least the turn of the century, although their role has been growing in recent years. Concrete slabs can be purchased or built, but there is a distinction between poured basements and concrete slabs. Concrete slab bases can be pre-manufactured, and then set in place after they have been dug. Basement foundation systems require additional steps to prepare the area.
When shopping for a slab foundation you need to consider both the thickness of the slab and the load-bearing capacity (LBC) of the material. The slab foundation system's LBC is the maximum weight the floor system can support without causing damage to the sub-floor or stressing it. The higher the load-bearing capacity, the better the structure will perform during severe storms or other types of weathering. In the worst case scenario, the LBC is the maximum load-bearing capacity of the concrete slab foundation system.
Next, consider the architectural design of the house. A concrete slab foundation should be able to support the weight of a house that will include a patio or a second floor. Also, keep in mind that if the house has windows and other penetrations into the interior of the structure, these will also need to be considered when selecting a foundation. The strength of the concrete slab foundation is dependent on the strength of the supporting structures, such as the walls, ceilings, windows, and doors.
One way to select a concrete slab foundation is based on its location. If the foundation is located where there is frost line, the best choice would be a floating slab. This foundation allows water to drain away from your house while still maintaining stability. A floating slab's concrete is typically perforated so that water doesn't penetrate the house. For instance, a five hundred square foot slab foundation might have six inches of perforated concrete so water could drain off at a rate of one inch per minute. At fifteen inches per minute, this rate of water draining would equate to approximately eleven inches per year.
On the other hand, slab foundations do not have to be completely concrete. One option would be to select an open system, in which the slab foundation would be constructed from a web of materials that are connected via tiebacks. The tiebacks are designed to resist corrosion caused by exposure to salt air, making them ideal for climates with high annual rainfall. The pros of this type of foundation are that there is no necessity of concrete and the installation is inexpensive.
Another type of foundation that can be used in residential applications is the raised slab foundations. These types of foundations are comprised of a base that is poured to form the structure and then a layer of wood or metal is added to the foundation. Concrete footings hold the foundation in place. This foundation has some advantages, such as the ability control the slope of the basement floor. These types of raised slab foundations have cons. They require continuous reinforcement by footings and are difficult to clean up.
A monolithic slab foundation might be one of the more desirable options available. Monolithic bases are simply pieces of concrete that have been poured into a circle or cone. It is difficult to distinguish between different pieces of concrete once it has set as each piece will have the same thickness. Another benefit to the monolithic concrete is that it is a very efficient way of constructing a basement. This foundation is also more cost-effective than other types. It doesn't require additional footings or reinforcements.
Whether you choose a slab foundation or another type of foundation is really a matter of preference. Ultimately you are going to have to decide what the advantages and disadvantages are of each one so that you can make an informed decision. In the end it will likely come down to your budget and your personal preferences. If you aren't comfortable with the crawlspace design suggested by your contractor, don't feel obliged to follow their instructions. To be satisfied with your construction efforts, you should have a well-designed, sealed, and maintained crawl space.