Underpinning is a method of strengthening and reinforcing the foundations of an existing building or other structure. It can be used to repair problems caused by movement of the building or underlying soil conditions (subsidence) or to increase the bearing capacity of an existing foundation system by adding more depth and/or width to the footings.
Whether you need underpinning or not is best determined by a qualified structural engineer, who can advise on the method most suitable for your situation. Typically the process involves excavating and removing soil directly under the foundations in controlled stages known as ‘pins’. This allows the soil to be replaced in a way that does not undermine the existing foundations, which would cause serious structural problems. The depth of excavation is also determined by the geotechnical engineer who assesses the soil composition and identifies the strata that’s suitable to hold the load.
After the soil is removed, the underpinning material is inserted into each of the pins (or short sections), and the concrete is poured. This forms a new section of foundation beneath the existing one and provides more support for the structure, which is then able to move independently of the old foundation.
The most obvious sign that your home needs underpinning click here is a visible lean or bow in the building. This can be caused by uneven pressure being applied to the building or by a change in soil moisture which affects how much the ground heaves and sinks.
There are other more subtle signs that your foundations may be in trouble. These include:
If you’re concerned about the state of your foundations, the first thing you should do is take a good look around the property and ask for advice from a few people. It’s worth remembering though, that even if you do identify some of the indicators above, none of them are a guarantee that your house will need underpinning – there could be other factors at play. If you’re still unsure, then it’s worth getting the advice of a professional structural engineer before you spend any money on repairs.