TM59 & Part O Overheating
Introduction
As global temperatures rise, the challenge of maintaining comfortable indoor environments becomes increasingly significant. Overheating in buildings is not just a discomfort; it can be a health risk and a major factor in reducing the usability of indoor spaces. Addressing this issue is vital for the building services industry. In the UK, guidelines such as CIBSE TM59 and the newly introduced Part O of the Building Regulations provide valuable frameworks for ensuring that buildings are designed and constructed to minimize overheating risks.
In this article, we discuss the importance of these guidelines, explore their requirements, and explain how they can be applied in practice to mitigate overheating in building services.
Why is Overheating a Growing Concern?
Overheating is a phenomenon where indoor temperatures rise to levels that are uncomfortable or potentially harmful to occupants. Factors driving this issue include:
Addressing overheating is crucial for ensuring occupant comfort, health, and productivity, and it is also a matter of regulatory compliance.
CIBSE TM59: A Benchmark for Overheating Analysis
The Chartered Institution of Building Services Engineers (CIBSE) Technical Memorandum 59 (TM59) is a critical guideline for assessing overheating risks in residential buildings. TM59 provides a methodology to determine whether a building is at risk of overheating, considering factors such as:
???????? Internal heat gains from occupants and equipment.
???????? Solar gains through windows and other glazed surfaces.
???????? Ventilation and cooling potential.
TM59 specifies two primary compliance criteria for residential buildings:
Criterion A – Bedroom Temperatures: Bedrooms should not exceed 26°C for more than 1% of annual occupied hours during the cooling season.
Criterion B – Living Rooms and Kitchens: Living spaces should not exceed 28°C for more than 1% of annual occupied hours.
Compliance with TM59 involves using dynamic thermal modeling to simulate indoor temperature profiles under realistic conditions. This simulation helps identify overheating risks early in the design process, allowing for effective mitigation measures.
The Role of Part O in the Building Regulations
The introduction of Part O in the 2021 update to the UK Building Regulations marks a significant step towards combating overheating in residential buildings. Part O establishes minimum requirements that apply to new dwellings and some major refurbishments, aiming to ensure that buildings are designed with overheating risks in mind.
The key principles of Part O are:
·??????? Limiting Excessive Solar Gains: This can be achieved by optimizing window size, orientation, and the use of shading devices to reduce direct sunlight during summer months.
·??????? Ensuring Adequate Ventilation: Natural or mechanical ventilation must be considered to enable effective cooling. In cases where high levels of external noise or pollution make opening windows impractical, alternative solutions such as mechanical ventilation with heat recovery (MVHR) may be required.
·??????? Location-Specific Risk Consideration: The regulation accounts for the building's location and other environmental factors, such as urban heat island effects.
Part O is designed to work in conjunction with TM59, providing a regulatory framework that supports the principles set out by TM59. When applied together, they create a comprehensive approach to overheating risk management.
Integrating TM59 and Part O into Design Practices
Designing building services that address overheating requires a proactive approach, integrating solutions from the outset of a project. Here are some strategies to consider:
Optimize Building Orientation and Shading
Careful planning of building orientation can reduce solar gains, while incorporating features such as overhangs, brise soleil, or external shutters helps to mitigate excessive sunlight.
Incorporate High-Performance Glazing
Low-emissivity glazing and solar control films can limit heat transfer while maintaining daylight quality.
Enhance Natural and Mechanical Ventilation
Designing for cross-ventilation or stack effect ventilation can significantly improve cooling, while mechanical systems like MVHR or chilled beams offer alternatives where natural ventilation is insufficient.
Use Smart Controls for Active Cooling
Installing programmable thermostats and automated window openings can help maintain optimal temperatures without excessive energy use.
By considering these strategies during the early stages of building design, it is possible to achieve compliance with both TM59 and Part O, while also delivering comfortable, sustainable, and energy-efficient living spaces.
Challenges and Future Considerations
The integration of TM59 and Part O presents challenges, particularly when dealing with existing building stock or complex urban environments where natural ventilation options are limited. Additionally, retrofitting for overheating resilience can be costly and technically challenging. Nevertheless, the shift towards more stringent regulations indicates a broader trend in the industry toward addressing climate resilience.
As we look to the future, building services professionals must continue to innovate and adopt new technologies, such as phase change materials, advanced passive cooling techniques, and smart building systems that adapt to changing conditions. Continuous monitoring and post-occupancy evaluations will also play a role in ensuring that theoretical designs perform effectively in practice.
Conclusion
John Francis MEP is an experienced Building Services Consultancy with a focus on sustainable design solutions, advocating for smart building practices and we are committed to improving standards in the industry.
We understand that the risks associated with overheating in residential buildings are real, but with proper planning and adherence to guidelines such as CIBSE TM59 and Part O, it is possible to create living environments that are both comfortable and resilient. These frameworks provide a foundation for designers, engineers, and developers to anticipate and mitigate the impacts of rising temperatures on occupants.
By embracing a proactive approach to building design, we can deliver spaces that not only meet regulatory requirements but also contribute to a healthier, more sustainable future. Let’s continue to build smarter, with the comfort and wellbeing of building occupants at the forefront of our designs.
If you have a project where incoming services is a consideration and would like to understand how we can support, please do not hesitate to get in touch.