Overview: Ranvir Singh and Kunle Barker meet eco-enthusiasts Rachel and Jake in Cambridgeshire. They are 10 months into transforming their 1960s three-bedroom house into an energy-efficient sustainable eco-home. With the majority of the green build done, Kunle offers up his design experience to tackle their open-plan kitchen and living room, which they've ambitiously moved up to the first floor to maximise spectacular views and to harness the solar power of the sun. For eco inspiration, Ranvir heads to Greenend House, an underground house in Buckinghamshire.