An ambitious couple set out to build a revolutionary eco home in the Cotswolds, which will not only use very little energy, it will also produce four times the energy it needs. Environmental consultant Duncan is planning to manage the project himself, moving out of the London home he shares with solicitor Liz to live near the site. But although he is totally committed, he has never faced anything like this before, and almost inevitably the technically complex 18-month build, while living apart takes its toll on the couple.

Kevin McCloud returns to West Sussex to meet with Olaf and Fritha who, in 2019, set out to build their own oasis on a piece of land that is boxed in by a railway line and an A-road. Due to an underground mains sewer, they were unable to build on half their plot and were left with a small triangle on which to build a three-bedroom house. They began with only £190,000 and were immediately surprised at the price of the sturdy retaining walls and foundations they needed to combat traffic vibrations and the sharp, pointed angles of the hand-built timber frame stretched Olaf to his limits. Kevin returns to see how life has gone for the pair and their new young daughter Lagertha in their triangular house.