Digging the foundations for your home - What you need to know
As with everything else in life, building a home requires getting the foundations right - if you don’t, nothing else will work.
Here are some of the things you need to know to avoid pitfalls. Even with the best preparations, however, foundations can be an unpredictable beast, so you need to have a contingency fund in case you run into unexpected issues once you start digging.
Do I need a soil survey?
A soil survey involves digging into the ground to see what the soil is like. It often isn’t necessary, as your architect or the council’s building inspector may know already, but if they recommend one, you should take their advice – not doing so could be a massively false economy. The amount of water in the soil, and how susceptible it is to changing, will affect the type and depth of foundations you need. You may also need to investigate evidence of radon, contamination or previous mining activity.
Strip or trench fill foundations – essentially trenches filled with concrete – are the default choice as they are simple, easy and relatively inexpensive. But if the ground is so difficult to work on that you need to dig more than around 2.5 metres deep, these types of foundations become impractical, dangerous for the workmen and very expensive. In this case piles – long columns driven down into the ground – or a reinforced concrete slab are likely to be the most viable options.
Trees near the site can absorb water and dry out the soil, contributing to subsidence. The National House Building Council publishes tables showing what are considered to be safe distances between trees and houses. If they are closer than recommended, you may need advice from a tree surgeon on what to do. Don't just cut them down yourself – this might cause the ground to swell with the water that's no longer being absorbed, damaging your home and others. Plus you can actually be prosecuted for cutting down a tree protected by a tree preservation order without permission.
Other things you need to know
If there are other buildings nearby, you need to ensure you comply with the Party Wall Act – which covers, among other things, the digging of foundations near someone else’s property.
Make sure your contractors are properly insured with an insurer regulated by the Financial Conduct Authority.
Your district or borough council's building control department will need to inspect and approve the groundwork at various stages, including before you start digging the foundations. You usually need to give them a day or two's notice, and your contractor should be able to do this for you.
With 13 years' experience in home design and construction, Kent and south east London architects Bluelime Home Design know how to make sure your home's foundations are firm and secure. We have offices in Dartford, Bromley, Erith, Bexley and Croydon – call us on 01322 517632 to chat about how we can help.