When a new building is constructed, if the builder and architect know what they’re doing, the foundations will be secure enough to support the structure. With some older buildings, though, either the original foundations were inadequate or, more often, the ground itself has changed in some way.
This may require the foundations to be strengthened. Various techniques for this exist, but they’re collectively known as underpinning — a word that’s so widely used today in its metaphorical sense that many people outside the construction industry don’t know what it really means.
When Is Underpinning Needed?
Older buildings weren’t always designed to today’s standards and can have few or no foundations. Although other design elements often compensated, an old building may have settled to the extent that it’s no longer secure. Alternatively, changes to a structure, such as adding an extra storey, may require stronger foundations.
It’s also possible that the ground has altered in some way, or that conditions such as repeated flooding haven’t been taken into account and have caused the structure to move. Subsidence can also result in foundations needing to be strengthened, and this can be either the dramatic examples we see in the news or more gradual subsidence.
How Does Underpinning Work?
There are several approaches to underpinning. The oldest method, which is still used sometimes for shallow foundations, is Mass Concrete Underpinning, in which small sections are dug out below the foundations, one at a time, and then filled with concrete. In an alternative method, a single concrete beam is inserted below the foundations to give extra support.
A newer approach, Minipiled Underpinning, can be more suitable for deeper foundations, for where there isn’t a lot of room to work or where ground pollution makes it unsafe to dig. It’s designed to deepen the load-bearing level, usually to between 5m and 15m, where shallower foundations wouldn’t give adequate support. Mini-piles of between 150mm and 300mm are either augured or driven into the ground and can support substantial loads.
Jet-grouting is another approach, where a resin or chemical compound is injected into the ground. This strengthens it by filling cavities and compacting the soil, providing a more secure base for the existing foundations.
An Expert Job
Underpinning is definitely not a job for the DIY enthusiast, or even for a general builder. The government’s Planning Portal points out that “If not carried out properly, this kind of work poses very real risks and could see damage to or collapse of the existing home” and recommends hiring experts — meaning a company that specialises in underpinning.
If you’re looking for an underpinning company to carry out work with minimal hassle and has experience contact us for a free quote, ASUC 12 year defects insurance and 38 years experience. Call us on 020 8805 4000 or email us at firstname.lastname@example.org