You not doing one of those Eco builds where houses seem to run on next to no energy? Or it a Barrat build?
All new buildings have to meet high level of insulation and low energy usage. My last 2 had B ratings on EPC. They would have got A if I decided to fit solar-that is the only easy way to oush a new house into the top band. Cost return for the top A rating wasnt worth the extra investment, they were gas heating. Hardly used much gas to get really warm house. All wet rooms and kitchen had underfloor heating .