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Raft and piled foundations

Engineering design plays an important role in these types of foundations. A L Ryder Ltd, will provide full design for all your piling and foundations works, suitable for Building Regulations and NHBC submissions.

There are four types of foundation: Deep Strip, Raft, Trenchfill and Piled. A survey will establish the ground conditions that will pre-determine the best foundation method to be used.

Raft Foundations

Raft Foundations can be a suitable alternative if traditional Deep Strip and Trenchfill foundations cannot be used. Raft foundations are used where the ground is inherently stable but where conditions deep below the surface, such as mining, might lead to ground movement. The reinforced raft is coast on top of consolidated hardcore and is shaped at the edge to provide a step upon which both leafs of the wall are constructed.

Raft construction foundation
  • These details assume that ground conditions permit the use of raft foundations, adequate ground bearing capacity to support structure exists and that ground is free from contamination
  • These details are not suitable where deep drains or trees can affect the foundation
  • These details are only suitable for single storey extensions to domestic buildings
  • The dimensions of the raft should be at least 3m x 2m and the longer dimension should be less than 1.5 times the shorter dimension. Internal stiffening beams, similar to the internal edge beam may be required
  • The ground must be well consolidated and capable of supporting a load of at least 50kN/m2
  • Different settlement rates should be considered where the extension abuts the existing building. Wall fixings between new and old brickwork, etc
  • Brickwork and blockwork should be suitable for use below ground level
  • Floor insulation is normally 125mm flooring grade polystyrene. 75mm may be used if a better insulant (such as polyisocyanurate) is used. 25mm edge insulation is needed
  • 90mm standard cavity wall insulation is used with 100mm aerated blocks or certain 100mm special aggregate block
  • Steel reinforcement must be lapped at least 450mm for both mesh and mild steel bars and provided with 40mm concrete cover

Please note that these guidance notes are for advice only and may not cover all situations. It is your responsibility to ensure that they are appropriate for use in your particular circumstance.

Piled Foundations

A pile is a type of foundation commonly used in property construction. Piles are used as a substitute for other foundation methods when earth around the property isn’t strong enough to support conventional foundations. Piles are used to stack up more layers of soil and keep them walled in, providing a firmer base.

Driven Piles can be made from different materials. Steel or wood can be used to make the piles but concrete is usually used. Driven piles are a popular solution as they can be adapted to fit different properties.

An advantage of using a Piled Foundation is that it can be arranged into different shapes to match the property they are designed for. Typical shapes when using concrete include squares, octagons and rounded cross sections. These shapes are usually reinforced and made from pre stressed concrete to provide extra support.

Piled construction foundation
raft foundation construction