If green belt areas and prime sites are to be avoided wherever possible, this means building on increasingly difficult ground conditions.
Building on brownfield sites, many of which lie on flood plains, is an obvious solution. But global warming has put the UK at a greater risk of flooding so the building of homes with firm foundations is paramount.
Abbey Pynford has developed a number of solutions to this problem. Among them are the Housedeck and Comdeck foundation systems.
"The Housedeck system helps housing developers to reassure buyers that their properties have a viable defence against flooding," says Abbey Pynford chairman and designer of the systems, Paul Kiss. "A well designed open area beneath the house has to be better than a metre of under build, as the area will dry out more quickly and be aesthetically much more acceptable. In addition, given that piles were required in the first place, this is a more cost-effective option."
The latest development using the system, which should be completed late this month, is Huff House – a two-storey building on a site adjacent to the river at Thames Ditton in Surrey.
Two storeys is within the capability of the Housedeck system, which is suitable for buildings up to, and including, five storeys in height. It can accommodate a range of variations to the foundation footprint, allowing for all piling methods – bored, driven or augured – as well as ground improvement techniques. There is also little or no spoil to be removed from site.
The system has a low construction depth, needing a structural reinforced concrete slab only 225mm deep that covers the entire footprint of the building. This is supported directly by the piles – between 140mm and 350mm in diameter – without the intervention of ground beams or pile caps. Steel reinforcement ensures that loads on the slab from the building's superstructure are transferred to the ground via the piles, without the risk of piles punching through the slab.
The contractor claims the voided system is ideally suited to complex brownfield sites that incorporate hazardous soil gases, such as methane, carbon dioxide, or radon, which are formed when uranium in soil and rock undergoes radioactive decay. These gases can also be present in greenfield sites because of naturally occurring organic deposits such as peat. The void also allows for ground heave in shrinkable or desiccated clay areas.
Housedeck can also help with hidden underground obstructions on-site too. Site investigations rarely locate all underground obstructions and all too often problems are discovered after the work has started. With traditional pile and beam foundations spaced in straight lines beneath the ground, there is little scope for changing the pile locations if an unexpected obstruction is found.
For heavier duty applications, Housedeck has a bigger brother – Comdeck – a similar system in principle, that is being installed on another riverside site at Luton Hoo, Bedfordshire. Abbey Pynford has been appointed groundwork contractor for the project. The £35M development will transform a listed Grade 1 property to provide an 81-bedroom function and conference centre.
Abbey's project manager on-site Mike Dorman says: "This four-storey complex is being built close to the banks of the River Lea. The weight of the building is on 6m or 7m of wet, silty soil and needs piled foundations.
"Using traditional piled foundations is not considered overly eco-friendly so our heavier duty proprietary piled raft style foundation system is being used. It's ideally suited to historically sensitive surroundings such as these, especially when we look like being on site for about three months in all."