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Q&As
Which build system works best with a sloping site?
I am looking to purchase a sloping site with fantastic view. The plot has quite a steep gradient and is made up of clay soil. Will my site impact my choice of structural system or can I work with whichever? Are there any structural systems that are better suited to steep sloping gradients and what are the key benefits of this?
One Answer
This is one of those situations where the honest answer is: it will… and it won’t.
If the slope is fairly shallow, you can usually deal with it entirely in the substructure. In other words, everything up to damp proof course can be designed to accommodate the gradient using stepped foundations and, where needed, some localised retaining. This effectively “levels the playing field” at DPC, meaning your superstructure choice is still largely yours. Timber frame, SIPs, masonry can all still work.
Where things start to change is if you’re building into the slope. If part of the superstructure of the house is acting as a retaining structure and is therefore in constant contact with damp ground, a masonry-based system such as blockwork or insulated concrete formwork (ICF) tends to be more suitable because it can deal with basement-type conditions (waterproofing, and lateral loads) more robustly than lightweight systems.
Regarding the ground itself, clay is actually a good bearing soil. However with clays movement is still an issue. Clay expands and contracts with moisture levels, so foundations need to be designed accordingly. If trees are nearby, you may be looking at deeper trench fill foundations taken below the zone of root influence. Either way, a proper foundation design is essential.