Foundations are crucial to a building’s structural integrity. With this in mind, getting the right foundations for your plot’s specific makeup is just as important as what goes on top of them - if not more!
Our experts will take into account your house design and ground conditions when they come up with a groundworks design for you. Having foundations designed specifically for both your ground and your eventual structure de-risks the foundation process. It results in backing from a structural engineer, insurance, and a ground investigation. Read on for an introduction into some of the different kinds of foundations.
Deep and Shallow
There are different kinds of foundations, some rarer than others. Foundations can be split into two basic groups, shallow and deep. Essentially, the less stable the ground is, the deeper the foundations will have to be. This instability results from the bearing capacity of the surface soils not adequately supportive of the weight of the eventual building. So, foundations have to extend down further until they reach ground that will support the house. Groundwater, unstable ground, clay soil, and sloping sites are just some of the things that will influence your groundworks design.
Strip concrete is the most common type of foundation. It involves filling trenches with concrete, adding blockwork on top and then building up from that. They are often necessary in areas of softer soils, like sand, because they spread out the load of the building over a greater area. They aren’t very suited to poor ground conditions, though, and they’re also low lying, so if you think your plot might be at a risk of future flooding, you might want to consider other options.
Also, once they get to below a depth of about 2 metres, strip concrete foundations start to become uneconomical. That much concrete is costly, and laying it at such a depth can start to become dangerous. At that stage, it’s worth considering a deeper kind of foundation.
Mass Trench Fills
Mass trench fills are usually employed in areas with stable ground because they rely on the sides of the trench, as well as the bottom, for stability. They’re particularly effective in areas where soil is composed of chalk or clay, and involve using concrete to completely fill the excavated area.
Along with piled foundations, these can be partial for plots where the difficult ground is only covering a portion of the area. They avoid the need to bricklay below ground, meaning excavation is not extensive, so are a popular option amongst self builders and large-scale operators alike.
Similarly, raft foundations are used in areas where the ground needs such a large bearing area that wide-strip foundations would be spread too far. They’re made of concrete and designed to ‘float’ on the ground beneath. Because of this, they’re useful in areas where ground conditions are poor. Rafts can also be used for extremely energy-efficient builds, since they achieve no thermal breaks and therefore no thermal leakage. Rafts also offer the opportunity for insulation to wrap up the sides to further increase the thermal efficiency.
A type of deep foundation, pile foundations are used to transfer the superstructure load down to ground with adequate support, and are also common in particularly large structures. They’re also helpful for a minimal impact. For example, if your planning conditions require you to keep a certain tree on your plot (or if you just really like it), opting for pile foundations will protect its roots.
These are by far the costliest option and are quite uncommon in much of the UK. They do have the added bonus of creating extra living space beneath your home, but be prepared for the hefty price tag. As you'd expect, building a basement also creates a lot more health and safety hoops for you to jump through, so think carefully about whether you really need a basement in your new home.
So that's the round up of all the different kinds of foundations you might find under your new home. The good news is that, with us, you don't need to memorise them all! At Potton we offer comprehensive groundworks design alongside your house design. This will ensure your foundations fix perfectly to your timber frame or SIPs structure, and of course that your groundworks have the load-bearing capacity that your individual design requires.