We have created this Foundation Help & Advice centre to answer your questions about GreenRaft and its insulated foundation solutions. We are also providing information on various foundation types to explain the reason why a particular foundation might be used or has been selected by your structural engineer.

This image shows one foundation solution. There are countless options to support your structure and our foundation help and advice centre is there to explain the many options

It is not an exhaustive list, so if you have a question that needs an answer, please let us know. Hopefully, we will add your question to the section.

There will be some linking between the topics where subjects overlap, This should give a better understanding of the various foundations and how they are used.

It is a huge topic, so you will also find links to other authoritative sites where more in-depth articles are available.

The main factors that influence what type of foundation might be used are the load of the structure, the bearing capacity of the soil, the width of the foundation upon that soil and other site conditions. These site conditions may be soil and strata mixtures, water tables, nearby trees or removed trees.

Help Centre Main Topics

Across the top are five topics related to foundations, that make up this Foundation Help & Advice Centre. The topics cover foundation types, foundation design, thermal performance, costings, and installation.

Pick which one seems most appropriate for your question and see if the answer is in there.

How to Build Insulated Foundations

Building an Insulated Raft Foundation: A Step-by-Step Guide


Insulated raft foundations are a popular and energy-efficient foundation choice for various construction projects. They offer superior thermal insulation, reduced construction time, and adaptability to different ground conditions. This guide will walk you through the basic steps of constructing one.

Important Considerations

  • Professional Involvement: While you might tackle some aspects of the project, having an architect and structural engineer is vital. They ensure a proper design tailored to your building and site conditions.
  • Site Evaluation: Conduct a thorough site survey to assess ground conditions, drainage, and potential obstacles.
  • Regulations: Comply with local building codes and regulations.


  • High-density XPS Insulation Boards: These form the base insulation layer and perimeter insulation.
  • Damp Proof Membrane: A plastic sheet to prevent moisture from rising into the foundation.
  • Steel Reinforcement: Mesh or rebar to provide strength within the concrete slab.
  • Concrete: Calculate the amount needed based on your foundation design.
  • Concrete Pump (Optional): May be required for large pours.


  1. Site Preparation:
    • Clear and level the construction area, removing vegetation and debris.
    • Mark out the foundation perimeter based on your design plans.
  2. Excavation:
    • Excavate within the marked area to the required depth specified by your structural engineer. Keep in mind the thickness of the insulation and concrete slab.
  3. Groundworks (if required):
    • If the ground is unsuitable, install ground improvement measures like a layer of compacted hardcore and sand.
  4. Insulation Placement:
    • Lay down a damp proof membrane over the prepared base.
    • Install high-density XPS insulation boards in multiple layers, staggering the seams to prevent thermal bridges.
    • Install vertical XPS boards around the perimeter to form the edge insulation.
  5. Reinforcement:
    • Place the steel mesh or rebar according to your engineer’s specifications. Use spacers to ensure proper positioning within the concrete.
  6. Service Conduits:
    • Position any necessary plumbing or electrical conduits within the reinforcement layer before the concrete pour.
  7. Concrete Pour:
    • Order ready-mix concrete or mix on-site. Use a concrete pump for larger pours.
    • Pour the concrete in a single, continuous operation to ensure a monolithic slab.
    • Vibrate the concrete thoroughly to remove air pockets and achieve a level surface.
  8. Curing:
    • After pouring, cure the concrete as per recommendations. This involves keeping the surface moist to prevent premature drying and cracking.

Additional Notes

  • Weather: Avoid construction during heavy rain or freezing temperatures.
  • Underfloor Heating: Insulated raft foundations are ideal for incorporating underfloor heating systems. Embed the piping within the concrete slab itself.
  • Finishes: Apply the desired floor finish once the concrete is fully cured.

Advantages of Insulated Raft Foundations

  • Excellent Thermal Insulation: Reduces heat loss and lowers energy bills.
  • Faster Construction: Compared to traditional foundations, leading to potential project savings.
  • Versatility: Suitable for various ground conditions and building types.
  • Reduced Risk of Cold Bridging: Minimizes thermal weak points.

Disclaimer This guide offers general instructions. Always consult with qualified professionals to ensure the construction meets specific building codes, structural requirements, and accommodates the unique conditions of your project site.