Underpinning a Building
Underpinning is a procedure used to stabilize a building that has a failing foundation. The most common reason for a failing building foundation is deterioration of the supporting wooden structure. The wood may begin to fail when it is exposed to moisture over time. In any case, the foundation must be repaired or the building will eventually collapse.
There are other possible reasons that a building needs underpinning, some of the reasons being that an additional story is being added to the existing structure, the building has moved due to a natural disaster or the supporting foundation soil has changed.
The first step required in the underpinning process is providing a permanent stable surface on which to place screw piles. The underpinning supports should only be placed under load bearing walls, beginning at the four corners of the structure and advancing inward. The recommended size of the concrete support is 3 feet long by 2 feet wide at a depth of at least 2 feet. The concrete must set up for a minimum of two days to ensure it has cured properly and is strong enough to support screw piles and the weight it supports.
Underpinning brackets must be used to ensure the screw pile remains securely in place as it is used to raise the foundation to its former position. In certain cases screw caps are used to connect the pilings to a reinforced concrete beam.
Any time the foundation of a building begins to fail, it is necessary to consult with a structural engineer to determine which method of underpinning is recommended. If proper corrective measures are taken before too much damage has occurred, a building can be stabilised and remain usable for many years.