Construction
Piled Raft Foundations
Our piled raft foundations streamline your project by saving time and money. Unlike traditional strip foundations or pile and beam, it provides flexible design options and efficient load distribution. It’s versatile for all construction types and comes with LABC, NHBC, and Premier warranty approvals.
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What Are Piled Raft Foundations?
Piled raft foundations combine reinforced concrete raft slabs with strategically positioned piles to create an efficient foundation system capable of supporting residential, commercial and care sector developments.
By integrating the load-spreading benefits of a raft foundation with the deep support provided by piles, piled rafts can often reduce excavation depths, simplify construction and improve overall project efficiency.
Piled raft foundations are particularly effective where:
- Ground conditions are variable
- Traditional strip foundations become uneconomical
- High groundwater is present
- Made Ground is encountered
- Clay soils present movement risks
- Settlement control is important
For many developments, piled raft foundations offer a more efficient alternative to traditional pile and ground beam systems.
Piled Raft vs Traditional Foundation Systems
| Feature | Piled Raft | Pile and Beam | Deep Strip |
|---|---|---|---|
| Excavation Volume | Lower | Higher | Highest |
| Construction Speed | Faster | Moderate | Slower |
| Settlement Control | Excellent | Good | Variable |
| Material Efficiency | High | Moderate | Low |
| Variable Ground Conditions | Excellent | Good | Limited |
When Should You Use a Piled Raft?
Typical Ground Conditions Suitable for Piled Raft Foundations
Piled raft foundations are frequently used where:
Made Ground – Sites with historic fill materials and inconsistent bearing capacities.
London Clay – Locations where shrink-swell movement can affect traditional foundations.
High Water Table Sites – Developments where deep excavation becomes difficult or costly.
Brownfield Redevelopment – Sites containing obstructions, historic structures or contamination.
Variable Ground Conditions – Projects where soil conditions differ significantly across the development footprint.
When to use piling with raft foundations?
When ground conditions dictate that ground bearing raft, and strip foundations (<1.8m) are not viable, then a piled raft becomes a cost effective solution.
Suspended raft foundations are typically shallow structures made of reinforced concrete, usually 225–300 mm thick, occasionally with local thickenings where highly concentrated loads are to be accommodated.
These foundations typically cover the entire footprint of a building including support to external balcony or canopy posts etc.
Our design team deliver efficient, integrated versatile solutions to overcome site constraints and design challenges such as exclusion zones around existing services, underground structures, sloped terrains, tree root protections zones and many others.
What are the benefits of Piled Raft?
Piled raft foundations provide a distinct set of advantages, particularly in demanding ground conditions and tight construction programmes.
They offer robust support through piles, enhancing stability, and flexibility, while the raft element improves efficiency and reduces costs of excavations, muck away, substructure brickwork & beam and block flooring, while maintaining or improving thermal performance
Suspended rafts are highly flexible, and the choice of raft foundation and pile type depends on factors such as building weight, soil characteristics, and specific structural requirements.
We set high standards in execution of our foundations which correspond in line with or above the published standards within the construction industry for acceptable tolerances in verticality and slab straightness.
Our RC elements such as raft, steps, updates and integrated retaining walls can be designed and detailed as watertight concrete, to meet the criteria for Type B waterproofing system when required.
RC raft serves as an effective barrier against ground gases achieving 2.0 points in line with the score points system as listed BS8485.This means sufficient cover against CS2 & CS3 regimes in combination with appropriately designed, detailed and installed membranes over the raft and/or ventilation system beneath (CS3 only).
Underbuild can be easily accommodated, with bespoke edge detail and steps in slab levels to accommodate external level changes and differences in finished floor levels.
As the raft construction limits excavation, ultimately the piled raft creates a safer, tidier working site. This makes it easy for follow on trades to progress with the construction of the superstructure either steel/timber/rc frame or traditional masonry.
Our in-house design team ensure that your project is designed with ultimate efficiency, minimising materials, leading to cost effective and environmentally sustainable construction.
As we build out the foundations ourselves, our ultimate aim is to provide a solution that is as simple and cost effective as possible, which in terms leads to cleaner, quicker & safer construction.
