The Merton Rule is a ground-breaking planning policy developed by the London Borough of Merton in 2003. The Merton Rule requires all new major developments to generate at least 10% of their energy needs from on-site renewable energy technologies. The implementation of the Merton Rule was ahead of its time and preceded many building requirements relating to energy generation and reduction. Although the emphasis was on generating energy from renewable sources the Merton Rule also had a profound effect on increasing the energy efficiency of buildings. This results from the fact that if you reduce the energy demand of your building then the scale of the renewable energy installation will reduce proportionally. Since the application of the rule in Merton it has gone on to be implemented within numerous Local Authorities in the UK and across Europe and became part of the UK national planning guidance (IEA, 2009).