David Sharpe from Thomasons explains what the foundations are, why they must be site specific and how they could impact on the design of a building.
Interview with David Sharpe
David Sharpe is not only a chartered structural engineer but also a certified Passivhaus designer. In this podcast he explains the extra consideration necessary when creating an ultra low energy building – eliminating thermal bridges.
What Are the Foundations?
The foundations are the part of the building where all the wind and weight forces are transmitted from the building into the ground.
Often they’re not that thought about because they’re the first thing that’s done and are then hidden and never seen again.
Foundations Have to be Site Specific, Guide the Design and Not Fight the Ground
It is important to have a structural engineer involved at an early stage to ensure the foundations are specific to the site, but also relevant and influential to the design of the building above ground. Having an understanding of the ground conditions could shape the building footprint, the weight of construction or the number of storeys.
The Choice of Foundation is Dependent on the Type of Ground
There are a huge range of ground conditions in the UK alone. An additional element that features when selecting foundations overseas is, as well as the various ground types, there can also be a need to consider risk of earthquake.
“The Best Site Investigation is About the Size and Depth of the Foundations You Want to Build!”
As this isn’t possible, structural engineers will use existing information available to them, such as geological maps, before digging trial pits and boreholes to give an insight into the ground conditions. The results give good enough information to give the likelihoods and risks, based on a balance of probabilities.
The Choice of Foundation Type Might Depend on Local Materials
There are three broad types of system: strips and pads, rafts, and piles. The ground will to some degree determine the system type, but the material used can depend on the local construction market.
Problems Can Arise When Extensions are Built on Different Foundations
If research hasn’t been carried out and foundations are used for an extension that are different than for the original building, homeowners can find for example that the spread footings move and cause cracks and building movement.
Insulation Should be Underneath for a Continuous Thermal Envelope
EPS (expanded polystyrene) tends to be the default insulation. It can cope with getting wet, is inexpensive, is a technically right solution and provides thermal insulation.
Creating Foundations with a Low Embodied Energy May Not Be the Priority
David suggests the industry does not currently have enough data on the whole life consequence of picking one material over another for the foundations. Creating a low energy building is therefore the priority over worrying about the embodied energy of the insulation material.
He suggests a rule of thumb that if something is expensive then it might be because a certain amount of effort has been required and that effort requires a certain amount of energy. It can be wise therefore to see if there’s a cheaper alternative that does the same thing.
Every Project Should Have a Structural Engineer
David believes that investing the time and money to engage a structural engineer early in a project will reap benefits later on. The extra level of certainty they can provide will enable the client to make the right choices, potentially saving money.
In order to find a good structural engineer David suggests speaking to some and finding one that will communicate in language that can be understood by the client, and also speaking to previous clients who they have worked with to gauge their reputation.
“Look Before You Leap”
The most important thing to consider is that you can’t guess about what’s underground, so try and find out. By getting the data right at the outset you can mitigate your risks, and make sure you don’t make costly mistakes by using the wrong foundation.
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