Common Reasons for Underpinning a Foundation

There are multiple reasons why underpinning may be necessary for your structure.

First, the original foundation of the building may have been poorly constructed or become weak or unstable over time. Underpinning can reinforce the strength of your foundation, providing greater stability and ensuring that your foundation will last over time.

Second, underpinning is often necessary when the usage of the structure is going to change. If the building is going to be converted for a more heavy-duty application, underpinning may be necessary to increase the capacity and reinforce the foundation.

Third, it can be a solution to problems with the soil that your structure rests upon. The properties of soil can change through consolidation or subsidence, which refers to the downward shifting of the ground over time. This can lead to the soil that is less suitable for the foundation of a building. Often times the most desirable building sites have extremely poor soil conditions and require deep foundations or piers to reach adequate bearing material.

Finally, underpinning may be necessary if you are building a new structure but have found that it will be more cost-effective to reuse the existing foundation. Underpinning will secure the foundation for continued use in the future.

Foundation Underpinning Methods Concrete

The concrete underpinning method consists of digging boxes underneath the foundation and pouring additional concrete into these boxes. This process requires a staggered installation process to essentially create a second foundation under the original foundation. This underpinning method works best if the original foundation is fairly shallow in terms of depth. Oftentimes, the soil is not suitable to support even the weight of your existing foundation. So by adding additional concrete weight, the settlement can actually be accelerated.

The concrete underpinning process can be very costly and time-consuming as the excavation around the home or building is left open while the concrete cures. Keep in mind that it takes 28 days for concrete to cure and fully achieve its strength. With today’s advances in technology, this process is very rarely used in repairing foundations and should alert any homeowner if a contractor offers this type of solution.

Beam And Base

Another underpinning method is called the beam and base. This technique is more advanced than the mass concrete method. It involves constructing a reinforced pre-cast concrete beam either above, below, or to replace the current footing. Then, mass concrete bases are put in place at predetermined locations, and the beam is installed to transfer the weight of the building onto these bases. Beam and base underpinning have the same disadvantages as the concrete underpinning method.