Building retrofit for enhanced energy efficiency is a significant and growing sector of the construction industry, a major source of investment and added value and a critical climate change mitigation strategy. However, despite the view of energy efficiency as a ‘low hanging fruit’ of climate change mitigation, the incorporation of sustainability principles to retrofit projects frequently represents a complex task, further complicated by the unique and multi-faceted nature of such projects. Optimal solutions need to accommodate building specific information, including factors such as: climate location, building envelope variations and diverse lifecycle impacts. At the project level, success may not be defined by a single criterion, but by the degree to which multiple criteria can be balanced, or competing criteria traded-off. Success can also vary depending on the priorities and perspectives of a wide range of stakeholders. The political dimension is therefore as important as the technical dimension. This paper forwards an appraisal framework which systematically considers the sustainability of retrofit projects, taking account of various project alternatives, stakeholder and expert input, building-specific characteristics, and criteria selection and weighting mechanisms. The paper is the first exploratory step in developing a comprehensive and integrated framework for evaluating alternatives for building retrofit projects, based on key sustainability principles. The forwarded Sustainable Retrofit Appraisal framework provides a means of appraising individual projects, taking account of multi-criteria performance across the entire lifecycle. Practically applied and timed appropriately, the framework can enable better decision-making and more efficient resource allocation for retrofit projects, which fully incorporate sustainability principles.