Most people are aware that Passive House construction is usually built on an insulated raft foundation.  Most people are also aware that post-tensioning allows for removal of virtually all rigid steel reinforcement and significantly reduces the volume of concrete required.

GreenRaft Insulated Foundations, CCL Post-tensioning and Kingspan Insulation have collaborated on this new innovative solution and developed what is thought to be the world’s first insulated post-tensioned raft foundation.

The first project is currently being constructed in Essex and will support a Kingspan Tek House on a GreenRaft passive raft insulated foundation.

Jon Machin, Chief Operations Officer (Europe) at CCL, which provides specialised engineered solutions for structures and are the experts in post-tensioning, said, “Although the use of post-tensioning (PT) in a ground bearing raft is not new, we don’t know of any that have been formed within an insulated envelope. In some parts of the world, especially the USA and Australia, a PT raft is a commonplace occurrence, especially where the soils are classed as expansive.  The PT solution also reduces the concrete required by about 30% and removes the need for traditional reinforcement, which is especially attractive in today’s volatile marketplace.  The cost savings this solution can achieve are potentially huge, and especially so in larger structures.”

GreenRaft’s Technical Director, Philip Grove said, “This is the culmination of months of work designing a totally new type of foundation.  The post-tensioned Insulated Raft delivers not only the perfect thermal envelope, but also the most effective solution for all those seeking to reduce their carbon footprint.  It is rewarding to see the interest that this innovative solution is now creating in the construction industry and is very exciting for all involved.”

GreenRaft’s insulated foundation system is different to all others on the market.  It has a high degree of adaptability as it is not made with pre-moulded parts.  The patented solution gives the ability to tailor the solution exactly to the design requirement.  For timber frame and SIP structures, the option of a built in upstand is proving particularly attractive.

The company insists on using only Extruded Polystyrene (XPS) or Foamed Glass as the insulation options.  “Extruded Polystyrene and Cellular Glass insulations are the only insulations that we will use in a below ground situation” said Philip Grove. “These are both insulants with high compressive strength and both with a high resistance to moisture.  The Cellular Glass is not the most efficient as an insulant, but it is totally fireproof, for those that need this option.”

GreenRaft can be contacted on 0845 8382181 or info@greenraft.co.uk, and thermal calculations and cost quotes can be generated directly from the website at https://greenraft.co.uk/greenraft-u-value-calculator/