EU policies to mitigate climate change set ambitious goals for energy and carbon reduction for the built environment. In order meet and even exceed the EU targets the UK Government's Climate Change Act 2008 sets a target to reduce greenhouse gas emissions in the UK by at least 80% from 1990 levels by 2050. To support these targets the UK government also aims to ensure that 20% of the UK's electricity is supplied from renewable sources by 2020. This article presents a design framework and a set of integrated IT tools to enable an analysis of the energy performance of building designs, including consideration of active and passive renewable energy technologies, when the opportunity to substantially improve the whole life-cycle energy performance of those designs is still open. To ensure a good fit with current architectural practices the design framework is integrated with the Royal Institute of British Architects (RIBA) key stages, which is the most widely used framework for the delivery of construction projects. The main aims of this article are to illustrate the need for new approaches to support low carbon building design that can be integrated into current architectural practice, to present the design framework developed in this research and illustrate its application in a case study.