House Footings and the Design Process

The type of earth you lay your foundations on can have repercussions for your house for decades after it’s been built, and for the course of its whole life – this is especially the case if you have a concrete slab floor.

To make sure that the right type of subfloor is built for your home, your site will need to be tested by a geotechnical engineer. The engineer will take soil samples from the site, subject them to varying tests and then specify the correct site classification according to Australian Standard AS 2870/2011 – Residential slabs and footings.

For all ratings, it’s simply a matter of building a subfloor that’s suitable for the soil type, and for the type, shape and size of house you want to build – and an engineer will be able to figure out what’s most appropriate for your design and the site you’re building on.

Most Class A and Class S sites will only need a basic reinforced slab with concrete beam footings underneath the edges of the slab, while sites with other classifications will require the slab to be stiffened. For slabs, this will require a series of cross beams in the slab – and sometimes piers too. This extra ‘stiffening’ helps to prevent the slab from bending and twisting as a result of moisture driven movements from underlying clays.

For ‘highly’ and ‘extremely’ reactive sites and problem sites (i.e. Class H1, H2, E or P), a structural engineer will need to do a special assessment and advise on how to safely build a house without the risk of damage due to soil movement. In many cases, this will involve installing concrete piers or screw piers into the ground underneath the footing beams on the slab for added stability and support, to a depth sometimes below the depth where soil moisture variations are minimal. Moisture variations tend to be lower at greater depth in clay soils.

If you have questions regarding building your dream home, speak to Australian Classic Homes on 8332 6099… we’d love to hear from you.

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