Commercial concrete

Things to consider when laying foundations

What are building foundations and why are they so important?

Building foundations – while not visible and below ground level – are one of the most crucial aspects of any build. They are used to ensure a building’s weight is distributed in an even fashion and to facilitate a solid footing for the building as a whole. Getting the footings and foundations right is paramount to avoid costly remedies later down the line, or, in worse case scenarios, even having to knock the building down and start again!

We’re here to guide you on the type of concrete and foundation needed to ensure your project is completed without a hitch. You should also work closely with a structural engineer and building control to ensure any footings you have plans for are appropriate for the building type / improvements you are planning.

Things to consider when laying foundations

Trees and soil:

Ordinarily carried out by digging a series of holes (trial holes) across your site, you can then use the analysis of soil type to judge general conditions for the location as a whole. It’s important to know the type of soil where you’re building, as certain soil makeups can cause subsidence and these need to be negated by building the correct footings and foundations.

Even trees have a role to play in your decision making. In simple terms, depending on various factors, the closer a tree is to a new building the deeper the foundations must be taken down. To give an example – poplar trees have a high water demand and can potentially cause serious problems to foundations in shrinkable clays and soils, which may lead to cracking and sometimes movement. Also, should you have an existing tree in your garden, having it felled will not mean that the foundations will not be affected – heave in clay soil can take place when it takes up moisture and swells after the felling or removal of trees and hedgerows. In these instances, your structural engineer will advise what is necessary to overcome these issues and, in extreme cases, it may be necessary to use a different type of foundation, such as piled or raft foundation.

Drainage and nearby structures:

Drainage issues close to foundations can be very expensive to rectify. The proximity to your project can make excavation works more difficult, even impacting the structural integrity of your foundations.

It may sound obvious, however the simplest way to negate problems with drainage pipes is to reroute the trenches that house the drainage a greater distance away from your foundations, if practical.

The important aspect to remember – if drainage is close to your foundations – is to make sure no further loads from your foundations are put on the trenches for the drains. You can avoid this by simply increasing your foundation depth

Types of foundations

You get shallow or deep foundations, mainly. Commercial projects often require deep foundations, to allow a greater depth of soil to support taller and larger structures.

Domestic projects on the other hand – for example for a new build home or extension – will only require shallower foundations, generally with less depth than the width of the property.

Types of shallow foundations:

Isolated footings / Pad foundation

These are designed to support an individual column and are either square, circular or rectangular. Created to carry concentrated loads, with the thickness worked out by assessing the weight of the load and surrounding ground conditions.

Combined footing

When two or more columns are too close together, such that if you used isolated footings they’d overlap, then combined footings are the solution. Rectangular in shape, the extra length allows more than one column to sit atop.

Strip foundation

These are used to support continuous or sometimes stepped above ground structures, such as a wall, or multiple closely spaced columns. A good example of when these are used is for house foundations or footings for conservatories and extensions.

Raft or mat foundation

This type of foundation will need careful design by a structural engineer to ensure it’s suitable for your project. It’s designed as a solution if you can’t use strip foundations for any reason.

Essentially, a raft solution gets its name because it’s a concrete slab that sits under the entire extension and ‘floats’ on the ground like a raft on water.

Types of deep foundations (most often more commercial projects):

Caisson – also known as pier / drilled shaft foundations

These are cast on site, where a column of the required depth is drilled into the ground, then the hole has reinforced steel lowered into it, which is then filled with concrete.

Pile foundations

When the ground close to the surface isn’t appropriate for heavy loads, piles are put into the ground and filled with concrete. A ground beam then is used to enable the surface to be built upon.

How to create your concrete footings and foundations

Before you start any project, it’s vital that you seek expert advice on the type of foundations you will need, from a structural engineer. You will also need planning permission for any major project involving the need for new foundations, and your project will need to be signed off by Building Regulations.

Once you’ve sought the appropriate advice, you are ready to do the following:

Get your ground ready, cleared and dug to the right depth

Mark out the area where your concrete is going to be poured, using string and pegs, allow an additional 50-75mm if you are planning to use formwork (which is what holds your concrete in place while it is curing).

Once ready, dig your foundations to the specified depth. If you have sufficient space at your property, this is much easier if you use a digger to do so Depending on the ground conditions, the stability of the side walls of the trenches may not be great and there could be a risk of the side falling in, particularly if heavy rain is forecast, so it’s important to get your Building Inspector lined up and concrete booking scheduled in advance, to avoid any such issues.

Once you’ve dug your foundations, You’ll also want to clear the ground of any stones / rocks / tree roots etc. and then level and compact the area. For floor slabs and isolated footings, you’ll want to leave enough depth for sub base (i.e. hardcore laid over the top of soil (approx. 100mm – subject to ground conditions), damp proof membrane (DPM), then the concrete itself.

Add your sub base and make it compact the ground again

Add your sub base and compact the ground, then add your Damp Proof Membrane (DPM) and set up your formwork for your concrete. Use our handy guide on laying concrete to guide you through this process.

Order and pour your concrete!

If you’ve followed the above steps, then you’re all set to order and pour your concrete. However, don’t forget to book your concrete well in advance to avoid any delays on site, you can always make a provisional booking and if necessary move your pour to another day if you have problems on site.

Our ready mix concrete lorries will deliver the exact amount you need to site and our concrete pumps will pump the concrete from the lorry directly into your foundation excavation. Simply get in touch and we’ll help you work out what you need to successfully complete your project.

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