In days past when ground conditions were bad or construction was taking place on brownfield sites or second-hand land Engineered Foundations were required and they were the exception rather than the norm.
They came in many forms; rafts, pier and beams, piles and beams, vibro stone columns and wide strip foootings, etc.
They were expensive, time-consuming, and, thankfully, only represented around 15% of all sites developed.
Times have changed and you may well think that the increase in building on brownfield sites and second-use sites (they’re not second-hand any more!) has caused huge cost increases.
Well, not so.
The market improvement, particularly in residential developments, coupled with the desire to increase significantly building on second-use sites has led to a revolution in the Engineered Foundations arena.
And that revolution is benefitting the developer to such an extent that the next 5 years will see Engineered Foundations as the norm rather than the exception, in other words there will be a full 180 degree U turn in the marketplace.
So why has this happened?
Like everything else there isn’t just one driver but many drivers...
Safety – we can no longer accept the excavation of deep holes and the prospect of somebody, whether employee, Building Control Officer, or, worse, a member of the public, venturing into those excavations with the inevitable potential catastrophic consequences. A trench just 1.0m deep can kill, and has done in the past.
Sustainability and the Environment – generally the material that underlies a brownfield site whether contaminated or not should be left there. Minimal excavation should ensue to produce nominal amounts of spoil for disposal. Costs well in excess of £150/tonne can be applied to the disposal to tip of contaminated material, and it only needs to be contaminated with loose bricks or old timber, nothing nasty! The really nasty stuff attracts a much higher premium. And is it right that we should transfer contaminated material to other parts when there are better ways of dealing with it.
Waste reduction – currently there is a tidal wave of initiatives to reduce and even eliminate construction site waste, and quite rightly so.
But wait just a minute; waste occurs in design as well as the on-site building process. The waste of natural resource in trenchfill foundations is huge. Aggregates, cement, water are all used in vast quantities to create concrete. As a very simple example, an average 3-bed house built of masonry construction methods weighs about 125 tonnes. If you need to excavate to 2.5m for the 50m of foundations under that house the amount of concrete used is...125 tonnes, i.e. the weight of the house is doubled! This is unnecessary and grossly over-designed; the factor of safety against failure is into double figures when it only needs to be 2 or even less, and trenchfill foundations do not guarantee structural integrity or stability.
Quality and reliability – if foundations go wrong and subsidence occurs costs of rectification can spiral out of control. Not to mention the emotional cost to the owners of the property which could be literally cracking up around them. Warranty providers are still allocating up to 30% of their claims pay-outs to sub-structure faults; and that doesn’t include subsidence due to poor ground conditions or changing ground conditions which is usually covered by insurance.
So how do Engineered Foundations deal with the complex issues of Safety, Sustainability, the Environment, Waste and Quality & Reliability?
- They minimize and sometimes eliminate altogether deep excavations thereby greatly reducing the risk of death or injury from collapses.
- Deep excavations create additional hazards on site particularly if they are not fenced or marked in any way.
- The less you dig the less you have to dump; lorry movements are dramatically reduced if spoil carted to tip is reduced and there is the added benefit of reduced landfill.
- The saving in natural materials when reducing the amount of concrete in the ground is huge; couple with this the reduction in processed natural materials, particularly cement (2% of the entire World’s CO2 emissions are generated from cement manufacture) and the benefits to health and the environment are equally huge.
- Engineered Foundations now take less time to install and therefore limited labour resources can be focused on other, arguably more important, aspects of the build process.
- Over 80% of all foundation failures occur with inadequate “traditional” foundations. Elimination of “dig and dump” will significantly reduce the cost of foundation and sub-structure rectification.
And then, of course, there’s cost. The designs, the materials, the plant & equipment used in Engineered Foundations have all been subjected to significant amounts of Research and Development, and Commercial Scrutiny such that the boundary of 2.5m depth that used to be the tipping point for Engineered Foundations to be considered is now 1.5m. This is a substantial change and should provide Developers, Builders, and Contractors with the confidence to look upon Engineered Foundations as the norm rather than the exception.
Roger Bullivant Ltd
John Patch is a Director of Roger Bullivant Ltd, the UK’s largest provider of Engineered Foundations for the Residential Sector.