Case study investigation of overheating in low-energy homes: insights from a post-occupancy evaluation in England

This paper presents evidence of overheating in present-day low-energy homes and explores the causes of this phenomenon. The study involved in-depth research on four low-energy homes in England. Three of these were newly built, while the other was retrofitted. Over a period of 11 months, the homes underwent environmental monitoring, and user perspectives were gathered. Additionally, a retrospective analysis was conducted based on the Building Regulations 2010 Overheating: Approved Document O. Overheating was primarily attributed to design factors related to ventilation (linked to both mechanical ventilation and natural ventilation), solar control (inadequate G-values), and the unique architectural elements (roof pod and sunspace). While most occupants employed adaptive behaviours whenever possible to cope with the high indoor temperatures, these strategies proved insufficient in preventing overheating in three out of four cases. The study also compared different methods for assessing overheating in low-energy homes. CIBSE-TM59 was found to be effective in identifying overheating issues and aligning with occupant perceptions. England Building Regulations Part O simplified method failed to account for potential overheating from deep energy retrofits, as well as possible exacerbations from roof pods and from transition spaces. Moreover, all assessments failed to encompass the elevated risk for (permanent or transitory) vulnerable occupants.