The concept of houses using the ground as part of their construction came to the attention of the eco-building scene thanks to the Earthship. Originally developed in the 1980s in Mexico, Earthship homes were built with reclaimed materials such as bottles and tyres. They faced towards the sun and were backed by a big earth mound to even out the building’s heat gains and losses.
In the UK the idea was taken up by pioneers such as the Hockerton Housing Project in Nottinghamshire, which was completed in 1998. With their thick insulation and modern ventilation systems, these homes brought the Earthship home concept up to date.
The idea of using earth-sheltering to create energy-efficient homes has been somewhat left behind by advances in construction. However, there are still reasons why a house might be dug into, or sit under, the ground. Sometimes the site leaves no other option – either because it is too steep to build on it in any other way, or because the planners want the property to be inconspicuous.
Some self-builds have turned this necessity into a virtue, with many benefitting from sloping sites that look out over fantastic views. Successful semi-underground homes have also been built to Passivhaus standard, so there should be no need to compromise on energy performance.
If you are pondering on whether to buy a sloping plot and build an Earthship home, the first question should be: is this the best way to go? For instance, if you want to use natural, breathable construction materials, retaining the ground away from the house may make the build more straightforward. Such materials need to be separated carefully from the damp earth – they are much better left open to the air.
On some sloping earth-shelter home sites it’s possible to level more of the ground. Instead of supporting the slope against the back of the house, the ground could be retained further back using terraced planting, gabions or a courtyard wall and creating a sheltered patio.
It’s worth investigating your options before making a final decision – preferably at the pre-planning stage. An initial half-day or day of preliminary advice from a structural engineer before you make an offer on the site could prove to be a great investment.
In any case, a thorough site survey before work begins is essential. A delay because the site collapses, or turns out to have an unexpected pipe, cable or watercourse, could do a lot of damage to your budget.
Get expert help
If digging into the ground turns out to be your best way forward, you will need the advice of a structural engineer as well as an architect. The structure of the earth sheltered home must be strong, well-insulated and waterproof. You need to have absolute confidence in the strength of the retaining structure, but an insulation or waterproofing failure underground will be very bad news, and may be almost impossible to remedy.