Today’s foundations are generally comprised of an intricate system of steel pilings or concrete piers–depending on the size of the structure, the soil beneath the foundation, and other factors. These projects have not always been the intricate systems that they are now; when homes were first built, they–and their foundations–were much simpler than they are today.
The Beginnings of Foundation
Without a foundation, a home would sink into the soil. To avoid this, the home would be elevated using pad stones to avoid sinking. This would put the weight not on the ground, but into the rocks, preventing the home from sinking.
Homes were also built with post-in-ground construction, also known as “earthfast” construction. Post-in-ground construction drives wooden posts into the ground that bear the weight of the structure.
Post-in-ground structures were simple but were not anchored well compared to today. The structures could only be anchored as far down as a person could dig. This created a shallow foundation that was trouble for early homebuilders. It was still a handy form of construction for those who needed a shelter fast. It could even serve as a temporary structure for settlers while a sturdier structure was built. There are still examples of “temporary” earthfast structures all over America. While they may have been temporary, some stand even today, though they still stand susceptible to soil movement.
As technology advanced, so too did foundations. The use of stone foundations expanded on pad stone theory and used a range of stones to help elevate and support a home. Building a foundation required a lot of stones to create a thick layer beneath a structure. The stones were densely packed to provide the greatest amount of support.
To gain the largest amount of density, builders would use rubble trench foundations. Rubble trenches pack pebbles and rocks tightly within a ditch. Instead of applying a thorough layer, a rubble trench is hollow in the middle. This puts all the weight on the outer level of the structure.
Water flow would sometimes plague rubble trenches and stone foundations. If water flow was too much, it could even sink a home into the ground. To avoid this, mortar would be used to seal the stone. Primitive forms of drainage would also send any groundwater away from the building.
Some builders still use stone foundations today, as it is an economical and resilient material. Ram Jack installs deep foundation steel piles. Deep foundations go deeper than the “zone of influence” soil layers that causes shallow foundations to shift: Shallow foundations are still prone to heaving or sinking and can cause damage to buildings that are improperly secured.
Early Wooden Foundations
As technology advanced, builders were able to use more malleable materials such as wood. One foundation that resulted from this was poteaux-sur-sol, which translates as “post on a sill.” Similar to standard post-in-ground techniques, poteaux-sur-sol would use wooden posts. The home’s frame would then hang off of the posts.
Instead of going into the ground, the poteaux-sur-sol rested on top of a sill. The sill would connect to the foundation, acting as a support frame. Also, the sill provided another layer of security between the home and the foundation. When the ground would shift, the sill would bear the brunt of any damage caused. This places all of the weight on something other than the Earth. The sill could still fracture and break, while deep foundation methods could make your structure more secure.
Later Building Styles
As building technology advanced, foundations were able to go deeper. The goal was to get a foundation below the frost line, which is the line of soil most affected by precipitation.
By the mid 20th century, builders were able to dig more than 100 feet into the ground. For the first time, builders could send metal pylons down into the ground to secure brand new skyscrapers. The Petronas Towers in Malaysia, built in 1996, still has the record for deepest foundation, going 374 feet into the ground.
Although the methods mentioned above were used for long periods of time, today’s technology and advances in soil studies help us engineer newer, better methods for providing a foundation to a structure.Geographic location is key in determining whether a shallow foundation will be acceptable and how long it might last. A basement type foundation found in Connecticut will not work in Texas. In fact, Texas soil requires deep foundations, as the underlying soil prevents shallow foundations from providing the strong footing a building needs.