The document discusses the embodied energy of retaining an existing concrete structure for a building conversion compared to demolishing and replacing it. It estimates that the existing concrete frame weighs around 6000 tonnes, containing approximately 7,800,000 MJ or 2,166 MWh of embodied energy. Demolishing and replacing the frame would require an additional 1,300 MWh of energy. By retaining the existing frame, the estimated 68 MWh annual heating requirement of the converted building could be met for over 60 years using the energy savings from avoiding replacement of the frame.