From Strip to Raft: Choosing the Right Foundation for Your Home Extension

Decided that you need more space? Want an extra room to use as an office? Well, whatever your reasons for wanting a home extension, you now have another to make – which type of foundation will you use for your home extension?

The foundation is what will support the weight and size of the extension above it. Not only that, but the foundation protects the extension against earthquakes, moving soil, and more. You may not have even realised that there are different foundations to choose from. Well, there are two main types and before you start building your home extension, you will have to decide which is the best option for your construction.

In this article, we’ll discuss the two most popular foundation options for home extensions: strip foundations and raft foundations, and explore their benefits and drawbacks.

Raft Foundations

Your other option is raft foundations which also go by the name of slab-on-grade foundations. The home extension is built on top of a foundation that is constructed of a thick concrete slab that could be up to 300mm in thickness. Supporting that slab is usually a layer of crushed stone and a damp-proof membrane. The latter is there to present against moisture making its way into the concrete.

If you are considering raft foundations over strip foundations, you will first want to know what this type has over the other in terms of benefits. Well, for one, these are a much better choice for larger constructions. You should note, however, that this is the most expensive option, so if money is a worry, you might want to go with a strip foundation instead. Additionally, the construction process is more complex than it is with strip foundations. Just keep that in mind when deciding.

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To increase the strength and stability of the foundation, steel reinforcement bars (otherwise called rebars) are used in raft foundations. These improve the foundation’s load-bearing capacity by countering tension and bending. This helps to prevent cracks and other damage caused by stresses on the foundation.

Raft foundations often make use of steel reinforcement bars to add increased strength and stability. By countering stresses such as tension, bending, and any shear bending, the foundation’s load-bearing capacity is greatly increased. Aside from increasing the overall str

Strip Foundations

Strip foundations are the most common type of foundation for home extensions in the UK. They consist of a continuous strip of concrete, typically 600mm wide and 200-300mm deep, that runs around the perimeter of the extension, with additional concrete pads under the load-bearing walls or columns.

This foundation technique often incorporates steel rebars as a reinforcement mechanism. The rebars are there for tension resistance, to stop bending, and solidify and forces exerted on the foundation. As for the depth and foundation, this is down to the type of soil as well as the structure’s weight. Normally the deeper these are the higher the cost.

Some advantages of strip foundations include their simplicity and cost-effectiveness. Furthermore, it is a popular solution that can be used with types of soil. However, steel rebar solutions will require additional planning and costs.

Another point worth considering is the strip foundation’s suitability for single-story and low-rise extensions. A key feature is that they have the ability to support light loads. However, they may not be sufficient for larger, multi-story extensions or in areas with unstable soil or high water tables.

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Choosing the Right Foundation

Both the above, as you can see, how their benefits and drawbacks. You just need to make sure you consider them all before deciding which to use for the foundation for your home extension. You should also consider your budget and timeline, as well as any potential building regulations and planning requirements.

In general, strip foundations are suitable for smaller, lighter structures on stable soil, while raft foundations are better suited to larger, heavier structures or areas with unstable soil.

The Takeaway

To sum up, choosing the right foundation is an important decision when planning a home extension. For instance, if you are planning a larger construction, using a raft foundation is probably the best bet. If you’re still unsure which to go for, consult a steel foundation specialist such as Heaton Manufacturing Ltd.