House Building Foundations Today

Every house building site across the land is different to the next, but each will have a common challenge with, probably, a different solution.

The challenge is to establish the foundations of houses to the best advantage, utilising the type of ground that is in place on the site.

In the majority of cases, land surveys will have predetermined the suitability of sites, leaving little to chance. Ground surveys will dig trial holes around the site and determine the best nature of foundation, but in some circumstances surprises can occur when the land is broken into.

Some features such as uncharted drains, old pits or covered wells can be found, obstacles unlikely to be insurmountable, but all carrying a cost to surmount.

The type of foundation that will be created depends on the nature of the soil, but the most commonly used at the moment is probably the trench fill method. This requires, as most trench work does, digging to a depth of approximately one metre, and 600m wide.

The trench is then filled with ready mixed concrete to ground level. The more traditional method is that of strip foundation, which requires the same trench work to be dug, and a layer of concrete poured in the base of it, to a minimum depth of 150mm.

The width has to enable workers to lay bricks, or usually blocks, up to the damp course level. It is considered normal practise to build off concrete 250mm thick to cover all eventualities in domestic build.

Some circumstances may require trenches to go down further. The proximity of trees, or existing drains and sewers, the make-up of the soil itself, are factors that may call for more depth, and therefore stability, however, once the level goes below around 2.5metres it becomes both uneconomical and dangerous to proceed with these methods

These situations, along with unforgiving soils which may be inherently unstable through water content, or made up of un-compacted aggregates or peat type soils, may require engineered foundations.

Engineered foundations are solutions determined by structural engineers, perhaps adding to the costings of the project, if not suitably surveyed previously.

Raft foundations are a straight forward answer to some circumstances, where a raft of concrete is poured over steel reinforcements to “float” on the ground below. This provides a building platform which evenly spreads the loads across it.

Pile driving concrete columns down to stable ground is a pricey but comprehensive method of establishing a stable base, topped with a ground beam to build off.