18 Jan What Is Underpinning?
All buildings need foundations to prevent them collapsing, and this shouldn’t be a problem for a new building. However, various things can happen to a building over its lifetime, and it’s possible that the original foundations won’t be adequate for the new circumstances.
In these cases, the foundations may need to be strengthened — or underpinned.
How Does Underpinning Work?
The most common reason for underpinning your house is subsidence, for example because of a cavity such as old mine-workings below or because the water-level is rising. However, it could be that an extension or an extra storey has left the foundations inadequate.
The various types of underpinning all have the same purpose — to provide solutions for redistributing the weight of the building to an adequate support. However, the various approaches do this in very different ways.
The Main Underpinning Methods.
- Mass Concrete Underpinning is the traditional approach, where sections are excavated below the foundations one by one and then filled with concrete. This tends to be a long and disruptive process, but it can be effective for shallow foundations.
- A less invasive process involves inserting a single concrete beam underneath the existing foundations to give extra support.
- Jet grouting has the advantage that no excavation is needed. This involves injecting a resin or chemical compound into the ground, which then fills any cavities and provides extra support.
- Mini-piling is now the underpinning method of choice in the majority of cases of subsidence. Here, piles are either driven or bored down through the weaker soil to a level of either firmer soil or bedrock that can support the weight more efficiently. Because it involves no excavation, it has the advantage of causing relatively little disruption.
Are There Any Drawbacks to Underpinning?
It’s possible that you’ll be advised by friends or relatives that underpinning your home is a bad idea. The two arguments they’re likely to make are that it’s expensive, and that your home will be harder to insure.
Underpinning is certainly an expensive procedure. If it’s as a result of subsidence, however, your building insurance may well cover the cost. In any case, the bottom line is that it’s far less expensive than having to rebuild your home after collapse.
Traditionally, there’s been a perception in the insurance industry that a house that’s needed to be underpinned is a greater risk. This doesn’t really make sense, since underpinning actually makes the building more secure, and a number of insurance providers now accept that. Although you may have to hunt a bit further for a good policy, it’s certainly possible to find one.
You’re very welcome to get in touch with us if you want to know more about underpinning.