It is easy to admire the parts of residential and commercial buildings that are evident to casual observers in Houston. However, very little is said of the foundation, which is that part of the structure that distributes the load to the ground below, ensuring structural stability. An experienced foundation contractor will stress the importance of building a structural base with the capacity to withstand both dead and dynamic loads, wind pressure and seismic loads.
Location Determines the Type of Foundation
Location-specific factors will determine the type of foundation most suitable for the project. These factors include height of the water table, frost lines and flood zone classification of the site. Susceptibility to storm surges, high winds and climate-related issues can limit the options when deciding on the type of base to build on. Soil type, availability and cost of land will also come into play when making this decision.
In general, it is best to choose the type of foundation that is used locally. Long-time residents and building owners would have noted any foundation issues, and zoning restrictions and building codes would already have addressed these issues.
Types of Foundations
A building foundation can be classified into slab-on-grade for temperate areas, a frost-protected foundation and T-shaped foundations for areas that experience seasonal freezing temperatures. Foundations can be below-grade, on-grade and above-grade with extrusions to provide crawlspaces or basement sections.
After the ground is prepared and the plumbing network is in position, concrete is poured directly on top of a layer of gravel to form the pad for the house or commercial structure. The edges of this slab are poured thicker to create the footing, and a wire mesh may be spread prior to pouring the concrete. The wire mesh minimizes cracking in the foundation.
A slab-on-grade foundation is commonly used in areas where the soil never freezes. The foundation can be anywhere between 4 to 8 inches thick with reinforcement bars strategically arranged to strengthen the foundation. Poured slabs are less expensive to construct, and they require fewer construction materials. Structures with slab foundations are easier to heat because there is no crawl space.
In areas that expect frost during the colder seasons, frost-protected slab-on-grade may be used. By insulating the concrete between two layers of polystyrene sheets, the pad will trap the heat from the ground and absorb the heat from the top. This type of foundation works only if the structure itself is going to be heated. A frost-protected slab foundation is recommended by concrete contractors because it is durable, sturdy and cost-effective.
In areas that expect the ground to freeze in winter, a T-shape foundation may be the best choice. The T-shape refers to the way the footing and foundation are constructed. The footing is built below the frost line, walls are constructed and then the slab is poured. Concrete should be allowed to cure adequately at each stage to ensure structural integrity.
A crawlspace foundation is a type of raised foundation where concrete columns and a concrete wall support the floor joists. A clearance of 3 feet or more between the ground and first floor creates a crawlspace for plumbing, wiring and ventilation ducts. Access to the home’s mechanical systems in this way makes for easier and less costly maintenance. Properly ventilated crawlspaces may help to keep the structure cooler during the warmer seasons. In flood-prone areas, adding flood vents to crawlspaces will allow the water to flow around the structure and prevent damage to the foundation.
The footing for basement foundations is constructed below the frost line, concrete walls about 8 feet high are erected, and a below ground level concrete slab is used as the basement floor. This requires below-grade excavation to construct, but it is the preferred design in areas where the water table and the soil type allow. It creates extra space for the home’s mechanical systems and storage space. The basement can also be properly finished to create additional living space.
Regardless of which type of foundation is best for your area, the foundation project will need to be permitted and inspected at various stages of the construction process. Before starting any type of construction it is best to check local build codes and consult with a qualified concrete foundation or paving contractor.