In order to make the right decision, it is first necessary to assess the foundation structure, the type of supports used and the exact cause of the foundation damage. Here is a summary of the most common scenarios when underpinning is necessary:

• When the original foundation is not as strong or stable as it should, often because the properties of the soil on which the foundation lays have changed.
• When adding an extra story to the building which requires an increase of the depth or load capacity of the existing foundations to support the additional weight.
• When repairing the existing foundation is more economical than building a new one.
• When stabilizing the foundation soils and/or its footings is needed due to earthquake, flood, drought or other natural causes which may have caused the structure to move or settle.
• Underpinning can be used both for construction and renovation
In order to make the right decision, it is first necessary to assess the foundation structure, the type of supports used and the exact cause of the foundation damage. Underpinning can be used both for renovation and construction.

Underpinning Methods

There are different methods and techniques that can be employed, depending on the type of soil, on its conditions, on the location and on the general state of the home or structure.

One of these methods involves the use of Helical piles or piers, steel piles with one or more helical formed plates. The piles are screwed deep into the soil and secured into more stable load-bearing ground. The tops of the piles are then connected to the foundation of the structure. The use of helical piers or piles requires minimal soil disturbance and movement and are preferred in projects that need to be carried out under such conditions.

Another method involves Caissons, sometimes also called piers, and they are used when the soil under the structure is very unstable or in swampy areas. These are usually hollow boxes or cylindrical steel reinforced forms, which are placed deep into more stable ground or bed-rock, and then filled with concrete. The use of caissons requires considerable excavation work and soil movement.

Grade beams are also used in foundation underpinning. They consist of reinforced concrete beams that transfer the load from bearing walls into spaced foundations such as pile caps or caissons.

Underpinning pads are often chosen for foundation leveling, rather than replacing the entire foundation. They are pads made of concrete and used to support sections of weak or damaged foundation footing.