Extension and full-house refurbishment of a locally listed, self-built, timber-frame "Segal House" in south-east London. We worked closely with the clients themselves - who carried out the majority of the construction work - as well as with Jon Broome, who assisted renowned architect Walter Segal on the original house in the 1980s. We maintained much of the existing fabric with the removal of existing ‘glasal’ external finish. We used a breathable construction externally for the retrofit with doubt about over insulating the building in terms of moisture transfer across the existing breathable walls. We were aware that by improving the airtightness this also increased the likelihood of condensation. The existing external walls had an estimated U-value of 0.64 W/m2K. With space and budget restraints we were led to overclad these walls with Steico-flex wood fibre insulation ensuring breathability. We achieved a high thermal performance improvement bringing the U-value to 0.24 W/m2K. Successfully applying the same adaptation to the construction of the existing roof which improved the U-value from 0.37 W/m2K to 0.18 W/m2K.