The Grade 2 listed Eleanor Lodge student accommodation building was retrofitted with vacuum glazing achieving a sufficient reduction in energy demand which in turn allowed the decarbonisation of the energy supply, in line with 2050 carbon targets. Outdated, carbon hungry gas boilers were replaced with a new mechanical ventilation heat recovery system designed to be distributed using the existing large chimneys. Working to a fixed Government grant budget and time frame all aspects of the decarbonisation proposals were reviewed and streamlined with construction specialists in a 2 stage tender. The contract was completed with continuous occupancy and a fast-track programme to minimise disruption in the College. Eleanor Lodge is one of several early College buildings at Lady Margaret Hall which characterise the campus. Designed by Sir Reginald Blomfield in 1924 in the English classicism style the red brick structure with stone dressings, sash windows and tiled roof is embellished with segmental pediments in the Gallic baroque style. Planning negotiations were managed with a Heritage Impact Assessment demonstrating negligible impact on the external character. Core holes of the existing structure were used to benchmark the thermal modelling which examined humidity flux and quantified the risk to the heritage structure of mould for different linings build up. Options for re-glazing were tested with a prototype room and reviewed with the Planning Conservation team and College stakeholders.