Combating Overheating in Residential Buildings
30th August 2023
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.
Compliance Methods
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.
Impact on Your Project
The new requirements are tailored to specific plots, influenced by factors such as aspect (i.e., whether they face North or South). Consequently, housing estates with standard housing types submitted for planning can face challenges. For instance, a standard house type with a north-facing garden may comply, while an identical house opposite with a south-facing aspect might require significant redesign to reduce the size of patio doors. A case in point involves a recent project where we are acting as Approved Inspector for an architect whose bespoke house received planning approval in 2021. Due to delays in contractor appointment, construction did not commence before the 2022 regulatory changes took effect, resulting in a failed assessment. A redesign is now needed to decrease glazing by nearly 12 square meters from the original design.
Another challenging scenario we have seen recently revolves around single-aspect flats arranged in a ribbon-like configuration on either side of a corridor. With one side having only south-facing windows and lacking cross ventilation, preliminary modelling is crucial to avoid the need for substantial redesign to create dual aspect flats.
Conclusion
Building Regulations Part O inaugurates a new era of residential building design, emphasising occupant well-being while addressing overheating concerns. Early engagement with building control is pivotal for navigating the evolving regulatory landscape successfully. If your project falls under the purview of Part O, seeking expert guidance is strongly recommended to ensure seamless compliance and optimal building performance.
Sources:
*Heat Mortality Monitoring Report: 2022 – GOV.UK
**Fire and Rescue Incident Statistics: England, year ending June 2022 – GOV.UK
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