During the summer of 2022, there were an estimated 2,985 deaths associated with overheating during heatwaves, marking the highest number in any given year since monitoring began. This information is available in the Heat Mortality Monitoring Report: 2022 on the GOV.UK website*. To provide context, consider that there were “just” 275 fire related deaths in the year ending June 2022**, underscoring the significant challenge posed by overheating.
Addressing the Challenge
As the construction industry adapts to address climate change, new regulations become imperative to ensure the safety, comfort, and efficiency of our built environments. An illustrative example is Part O of the Building Regulations, which was introduced in June 2022.
Part O represents a pioneering initiative that specifically targets overheating in new residential buildings. The core objectives of Building Regulations Part O encompass two main aspects: mitigating unwanted solar heat gains in the summer and equipping indoor spaces with efficient heat dissipation mechanisms, preferably without relying on air conditioning.
The scope of Part O extends to new residential buildings, encompassing shared communal areas and common spaces within these structures. Additionally, live/work units that accommodate both residential and commercial functions fall within the purview of Part O. However, it’s important to note that currently, highly glazed extensions to existing dwellings are exempt. Designers working on such extensions still need to perform heat loss calculations and are advised to also assess heat gain to prevent the extension from becoming uninhabitable during summer heatwaves.
Part O provides two avenues for compliance: the Simplified Method and Dynamic Thermal Modelling.
Simplified Method: This assessment involves evaluating the feasibility of cross ventilation (openings on opposite facades). Based on this assessment, guidelines are provided to control solar gains and manage excessive heat. Specific tables dictate parameters such as maximum glazing area, shading prerequisites, and minimum window-free areas. Compliance is assessed using a checklist found in the appendix to Part O.
Dynamic Thermal Modelling: This more flexible approach requires specialized modelling and software aligned with CIBSE TM59 standards. Through Dynamic Thermal Modelling, assessors create intricate computer models and reports that demonstrate daily compliance.
Part O also recognizes the influence of external factors on the effectiveness of overheating mitigation strategies:
Noise: Buildings in noisy areas must consider the likelihood of closed windows during sleep hours. Noise assessments may be necessary to ensure noise thresholds are not exceeded.
Pollution: Proximity to pollution sources requires adherence to Part F guidelines, aimed at minimizing pollutant intake.
Security: Security risks associated with open windows during sleep hours need to be addressed, particularly for ground floor and easily accessible bedrooms.