In construction, underpinning is the process of strengthening and stabilizing the foundation of an existing building or other structure. Underpinning may be needed for a many of reasons:
- The original foundation is not strong or stable enough.
- The usage of the building has changed.
- The type of soil supporting the foundation may have changed (possibly through subsidence) or were misjudged during planning.
- The construction of nearby structures causes the excavation of soil supporting existing foundations.
- It is more economical, due to land price or otherwise, to work on the current structure's foundation than to build a new one.