When it comes to any construction project, the foundation cost is the element that can be the most difficult to calculate. And you certainly aren’t alone in that when it comes to property development and building companies. Why?
Well, for the simple reason that regardless of whether you are building an entire house, a conservatory or even a garage, you need to know the condition of the soil as it’s the quality and type of soil that will determine the type of foundation your building will require.
You can rely on local information for the soil type, but the best option is to dig a trial pit to confirm the soil type and the depth of the subsoil.
We have found here at Kisiel Group that costs can change if you only have the basic information available on which to price the costs. Yet with full structural drawings (allowing for specific reinforcement or concrete mixes) the foundation costs can be calculated with more accuracy.
Comparing Foundation Costs
The majority of building companies – will give an average foundation cost. This will be based on the size of the project and what is termed a deep strip foundation. By that we mean the trench dug will be 600mm wide and 1,200mm deep to accommodate the external walls. Internal walls are calculated to have a minimum 225mm of concrete tamped level.
When you contact us at Kisiel Ltd we try to simplify the foundation cost of a new installation for you by providing a breakdown of the type of expenses you can expect. Our managing director Lukasz Kisiel believes only then will you really get an idea of what is involved in the different types of foundations available.
What are the factors affecting the installation of new foundations?
Be aware that the type and size of your foundations must be included in your planning application to the local authority. This means they must in accordance with current Building Regulations – otherwise your application will be rejected.
This is another check too since those working in Building Regulations will probably be more familiar with the soil type than your builder (if he/she is from out of town). In fact, most local authorities in the UK have a fact sheet on the different types of soil found in the region, with suggestions for foundation solutions.
Things to consider when planning your groundworks
One issue in the UK that can impact on the foundation cost in comparison to building in Europe or other warmer climes is, of course, the weather.
Due to the amount of rain we get here in the UK, it makes sense to fill the excavations to within 200mm of the ground. That way you can get the job done in one day and without having to worry about wet ground conditions. It means using more concrete, but it doesn’t add to the foundation cost too much.
The size of the building will, of course, have an impact on the foundation cost. So too will the type of foundation you plan to lay. Other factors, such as how easy – or not – the site is to access also play a part when it comes to the overall foundation costs. Remember, as well as the cost of building the actual foundation there will also be excavation costs for creating the trench too.
Cost of foundations per metre
Then there is the cost of the builders for your project. They tend to quote labour costs based on the size of the project. This can vary – depending on where your project is based – to anything from £100 to £150 per metre in the UK.
Another big differential is whether or not there are trees around. That’s because the depth of the trench will need to be extended to three metres – especially if the soil has a lot of clay in it. The moisture from trees affects soil in a couple of ways – either causing the soil to contract or expand.
Unreliable soil like this can, in turn, necessitates the use of a slip membrane or for the trench to be filled at one or other end with compressible material to make sure the soil doesn’t move over time.
What are the different types of building foundations?
There are four basic types of foundation you can choose from – raft foundations, trench fill foundation, strip foundations and concrete slab foundations.
The following is a more detailed explanation of the different foundation types:
Trench fill foundations
The easiest type of foundation to build, a Trench foundation involves filling the hole with concrete just below ground. The concrete costs are offlaid by the low labour costs.
Concrete slab foundations
Made from blocks of concrete (or sometimes poured over the area) Concrete slab foundations are very robust and not expensive to lay. Concrete slab costs reflect this.
A Strip foundation involves laying concrete on the base of the trench then building up to ground level with blockwork. At that point bricks, stones etc can be laid.
A Raft foundation is particularly effective where there isn’t much soil pressure to build on. Like the Strip foundation it also involves creating a solid concrete base, but this is achieved by pouring concrete on top of the soil rather than into a trench as if you were pouring concrete walls.
Why is subsoil important?
Soil (or subsoil) in the UK can be divided into various different types. These are rock, clay, sand and gravel, chalk, peat, firm clay (rather than soft) and filled ground.
Comparison of foundation costs
As you would expect, the larger the building you plan to construct, then the bigger the foundations and the higher the cost.
The cost for a strip foundation is around £100 to £120 per metre. For a trench fill foundation, you will pay slightly more at from £120 to £150 per metre.
As an example, a foundation for a building measuring 7x10m could cost as an average of £4,154.44 for a deep strip foundation. A trench fill foundation would be slightly more expensive at £6,356.63 and a 2m deep fill foundation would be almost twice as costly at £11,560.34. The costs are inclusive of plant, materials and labour.
It isn’t possible at this stage to calculate the cost per square metre for either Raft or Concrete Slab Foundations since there are too many variables at this early stage.
Key takeaways when analysing new foundation costs
The type of soil on which the building will be built is one of the biggest determinants when it comes to the choice of foundation. The other main impact on foundation costs is the size of the building itself. Then there is your location (with London builders being more expensive than those in northern parts of the UK).
Expect to pay up to £120 per square metre for foundation costs. The overall cost will depend, of course, on the size of the foundation. Whether there needs to be extra reinforcing carried out because of poor soil, this will also impact on foundation costs. So too with poor access to the site.
Permissions are necessary prior to start foundation work. This is from the local authority in question and if there is party wall work the neighbours must be consulted.
Get more information on foundation costs and what is involved in the construction of a building from the team at Kisiel Group Ltd.