Deep energy retrofit can improve historic buildings’ indoor environmental quality and protect them from decay and obsolescence while reducing their energy use and related greenhouse gas emissions. Although this practice has been growing internationally, in Aotearoa New Zealand there are currently no policies or initiatives to encourage energy retrofit in historic buildings and no substantial examples of projects. Most retrofits currently focus on much-needed earthquake strengthening, due to high seismic risks and national policies which mandate all existing earthquake-prone buildings to be either structurally retrofitted or demolished over the next decades. As seismic upgrade projects are widespread, this study explores the potential of applying energy retrofit concurrently with seismic strengthening, with a focus on unreinforced masonry (URM) – the main type of earthquake-prone historic construction in the country. The research investigates three case studies of listed heritage URM buildings using Post-Occupancy Evaluation and simulation. Their current performance was investigated, and retrofit scenarios were analysed through energy and hygrothermal simulation, utilising the EnerPHit standard as a guide. The energy models demonstrated a potential reduction of up to 92% in heating demand when comparing the most comprehensive retrofit scenario with the baseline in the coldest climate. The potential energy savings from each intervention were balanced against their heritage impact, based on the standard EN16883:2017. The study provides a methodology for balancing several considerations in integrated retrofit to make historic buildings more resilient not only to seismic threats, but also to a changing climate, while keeping a respectful approach to heritage.