How to Choose the Right Foundation Types
Erika Oppenheimer, a renowned test prep coach, is quoted as saying, “Without a solid foundation, you’ll have trouble creating anything of value.” Although she relates this to creating maximum value when taking academic tests, it can be applied in the more literal sense when it comes to choosing the best foundation for an owner’s building or for your own home. In order to maximize the value of a building, the most critical initial step is to research foundation types and choose the most effective foundation for your building project.
From the Ground Up
According to the Soil Mechanics in Engineering Practice, a foundation is defined as the lower section of a building structure that transfers its gravity loads to the earth. This basic definition is then broadened when considering foundation selection criteria, which is dependent on two main factors:
- Ground/soil conditions
- Types of loads from the building structure
The Constructor – a civil engineering information resource site – recommends conducting a soil investigation for your project to find out:
- Nature and type of soil
- Depth of different layers of soil
- Bearing capacity of the soil at varying levels
- Level/slope of the ground
For example, when the soil close to the surface is not capable of supporting structural loads, hard strata (soil layer which has sufficient load bearing strength) must be found and most often results in the need for deeper foundations. In other cases, where there is uniform stable ground, a shallow foundation would suffice.
Load Types from Buildings
Loading conditions that affect selection of foundation types depend on the type of building for your project, locational/environmental factors and the type of structural construction materials used for your project. The Constructor cites factors that increase loads and necessitate deeper foundations, including:
- High-rise/multi-story buildings
- Exposure to strong winds or earthquake zones
- Reinforced concrete buildings
Putting it all Together
Once soils have been investigated and loads types have been determined for the building project, now is the time to put it all together and select the best foundation type for the project. These main foundation types include:
- What it is: foundation type where the base is wider than a typical load bearing wall
- Why it’s used: The wider base distributes the weight from the building structure over a greater surface area and provides more stability for the building
Drilled pier/deep foundation
- What it is: type of deep foundation used to transfer heavy loads from the building structure to hard rock strata
- Why it’s used: Can reduce the amount of ground disturbance, all while protecting against earthquakes and wind forces; also used where highly expansive near surface soils are present
Post-tensioned slab foundation
- What it is: type of foundation that is spread across the entire area of the building to support loads from columns and walls
- Why it’s used: Can be used on expansive soils
Best Foundation Types in Colorado Construction
According to the Colorado Geological Survey (CGS), expansive soils are a major issue faced by contractors in Colorado. CGS cites that clays cause more property damage than any other natural hazard. When exposed to water, they expand up to 20% by volume and exert up to 30,000 pounds of force per square foot, resulting in a contractor’s worst nightmare.
When selecting the best foundation type for buildings in Colorado, several factors must be considered. Post-tensioned foundations can be used to spread the structural building load over a wide area to help prevent damage caused by expansive soils. This type of foundation can be costly and can require over-excavation.
Drilled pier/deep foundations can be used on highly expansive soils; however, these typically require additional costs for structural floors at base mounts.
Another solution for highly expansive soils includes a foundation type recommended by RMG called Tella Firma. The Tella Firma process elevates the slab above ground, thus creating space that protects the slab and structure from the shrinking and swelling of our Colorado soils. The void between the ground and slab allows the soil to expand and contract as it absorbs moisture then dries.
Benefits of Tella Firma foundations include:
- Multiple structure type uses, such as residential, multi-family or commercial projects
- Environmentally friendly foundation with no chemicals used and no waste
- More affordable option and takes less time to complete than most traditional suspended foundations
To create something of value, a solid foundation is required. When planning for your next building project, be sure to select the best foundation type that not only meets the soil conditions and load types, but also helps to save time and money on the project.