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Last edited 12 Jan 2021
Modular construction from the groundworks up
The term 'off-site construction' conjures images of buildings being put together on the factory floor, with just a short process to install at the site. This is one of the major advantages of off-site construction, which also improves on site health and safety and reduces disruption.
In fact, the work that takes place on-site is equally important. Much like traditional building, modular construction requires appropriate foundations to ensure that the structure stands the test of time.
Careful preparation is required on-site to ensure that the modular building can be installed within the desired time frame, so it is important to research the nature of the ground on-site and design the foundations to best suit the building being commissioned. Commissioning a ground investigation before putting the project out to tender will help avoid delays later in the process.
With traditional construction, perimeter walls and interiors load-bearing walls need substantial foundations to support the load of the structure, requiring significant excavation. Modular buildings require a different approach to groundworks as the foundation load is distributed across the whole of the footprint.
A ground survey will flag up any issues with the site, such as a significant layer of clay or soil on the surface that will require excavation. Once this is established, the modular building manufacturer will instruct the structural engineer to advise on the best response, allowing the development of the correct solution from the beginning.
 What are the foundation options?
For simple sites with no complications, all that is required for a modular building is a shallow excavation topped with a layer of concrete, with flags or blocks on top. This should take no more than two weeks to achieve, and is the ideal scenario for projects where a quick installation is necessary. In some cases, a single concrete pad isn’t appropriate, and in that case it may be necessary to use five or six long trenches with pads on top.
Where there is a layer of soil, clay or other unsuitable material on the surface, it is generally advisable to excavate to around 18 inches deep, then lay a concrete raft and positioning pads on top – all of which can be completed within around three weeks. This approach minimises excavation and spreads the finished building’s load across the full footprint of the building.
However, even sites which require more complex groundworks can be made suitable for modular buildings. Projects have been completed where there was a five metre deep layer of soil, a problem which was circumvented by installing piled foundations.
While groundworks for modular construction are generally simpler than for traditional buildings, issues may still arise if the land is lower quality than expected, or if the project team are unfamiliar with off-site construction methods. Off-site construction companies are generally willing to work with designers and contractors to find the right solution, but there are advantages to appointing a company which offers a turnkey solution.
Appointing a company which offers design, groundworks, construction and installation can save specifiers valuable time and money. When managing the process from design to completion they can collate prices – including groundworks – and present the final cost to the client, allowing them to control costs.
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