A recent study by Linda Toledo et al. investigated overheating in four low-energy homes in England–three newly built and one retrofitted. Over an 11-month period, the researchers conducted environmental monitoring and gathered occupant feedback to identify the causes of overheating. They also carried out a retrospective analysis based on the Building Regulations 2010 Overheating: Approved Document O.

Overheating was largely driven by 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 manage high indoor temperatures, these strategies proved insufficient in preventing overheating in three out of four cases.

The researchers also compared different approaches to assessing overheating risk. The CIBSE TM59 method effectively identified overheating and aligned with occupant perceptions. In contrast, the simplified approach in England’s Building Regulations Part O failed to account for potential overheating from deep energy retrofits, as well as possible exacerbations from roof pods and from transition spaces. All assessments failed to encompass the elevated risk for (permanent or transitory) vulnerable occupants

For more details, refer to the full study here.