Milenko Milenkovic, a Serbian engineer and inventor, has unveiled his eco-friendly house, 40 kilometers south of Belgrade.The dome-shaped construction 18 .5 metres in diameter and provides 220 square metres of living space. It also around 80% more energy-efficient than a conventional house of the same size. A section of the roof has grass growing on it to make it even more environmentally friendly. The house features two layers of walls, so that air can circulate between the two; improving insulation both from heat and cold. The house has an indoor swimming pool and even an indoor garden and Milenkovic says that the savings in electrictiy mean that his investment will have paid for itself in just four years. But this hosue is only the beginning. Milenkovic’s next project is three times bigger and he says energy costs for heating and cooling will be 50% lower than those of a conventional building.