Policy on domestic thermal retrofits is usually designed as a top-down enterprise, setting standards and inducing homeowners to retrofit accordingly. Its underlying assumption is that correct retrofit technology is developed by experts and comes down through supply chains to households, who apply it as designed to their properties. However, this model is challenged by the insight from socio-technical systems studies (STST) that technology and society mutually form and influence each other at every level of society. Using this conceptual framework, this study investigated whether innovations are happening among retrofitting households, and what support these have for diffusion upwards into supply chains and outwards to other households. Qualitative data was gathered through semi-structured interviews among homeowner-retrofitters plus building professionals and citizens' initiatives which support these, in Cambridge, UK. Local innovation was found in the development of new retrofit technology and novel reconfiguring of existing solutions. Much of this was triggered by clashes between standard retrofit solutions and heritage or aesthetic values, economic necessity, or building professionals' lack of knowledge or experience. The findings suggest that instead of treating homeowners as passive recipients, UK thermal retrofit policy should broaden to identify useful innovations developed by homeowners and support them where appropriate. (C) 2014 Elsevier Ltd. All rights reserved.