PBC Today sat down with Jason Bennett, national business development manager at Zehnder Group, to discuss Approved Document O and its importance in preventing overheating in buildings
Within the UK Building Regulations, Approved Document O provides guidance to building designers on mitigating overheating in residential buildings and reducing these effects.
As part of our collaboration with CIBSE Journal, we conducted a survey among consultants, contractors and building engineer professionals to explore the challenges they face when interpreting the technical requirements of Approved Document O. The challenges range from its complexity, to navigating performance-based requirements.
It is essential to understand the background of Approved Document O. Its guidelines are built to reduce the risk of overheating, but it’s not as simple as adding air conditioning or a ventilation system.
What are the main challenges that building service engineers face in understanding the guidelines of Approved Document O?
There are broader issues to consider, such as how they apply energy efficiency into the build programme. Achieving this balance can be difficult, as engineers must ensure the right systems are in place to comply with these guidelines, without increasing the carbon footprint of the project.
Engineers must also account for various site-specific factors. For example, acoustic considerations are important not just in major built up areas but also in urban environments, near farmlands or along busy roads. It is about finding the right balance between managing overheating in the summer months, but also maintaining comfortable conditions in the winter months.
Another challenge can arise from changes in compliance standards. As projects move through the different RIBA stages in a build programme, regulations can change. While Approved Document Part O might remain consistent, other regulations, like fire compliance, are constantly evolving.
This means that not only are engineers having to stay in touch with the different technologies, but they also need be aware of any compliancy changes as the project moves forward. For example, if I need to put fire collars on a ducting system, do I now need to change my design completely to allow that to fit into the build in a compliant manner?
Another key challenge is communicating with designers, who may not fully understand the importance of these regulations. Some will have quite happily been building using traditional methods for many years and are now facing the need to address overheating risks, which come with added costs.
Navigating these conversations to ensure projects stay within the budget while meeting the new requirements is a significant part of the engineer’s role.
©iStock | sturti
How can the industry then support engineers in understanding and applying Approved Document O?
We’ve been talking to many colleges and universities across the UK to try to implement these concepts into the curriculum. The idea is to start early, teaching students between the ages of 16 and 19 about the principles of overheating prevention and why these strategies are vital to building programmes.
It’s not just about putting bricks together. We want to ensure the new generation of architects, consultants, developers, and contractors learn and understand why these different strategies are needed and how to apply them to a building programme.
Enhanced training and education only begins once we’ve taught them how and why you need to apply Approved Document Part O practices. Through workshops, seminars and CPDs (Continuing Professional Development Programmes), we are committed to supporting the industry, covering not only ventilation systems but also the whole methodology for managing heating, cooling and energy efficiency as well as indoor air quality.
As a founding member of Passivhaus, we also teach those principles to Passivhaus. It’s about developing practical guidelines—they need to be available to everyone and in any language that’s understandable.
This isn’t just an issue for the developers, consultants or contractors, it’s also about the end user.
The worst thing that can happen is that Approved Document Part O is handled to the letter, and a ventilation system is installed, but then the end user turns it off.
Not only are you not providing any form of ventilation in the property, but the occupants are also putting their health at risk because of the risk of overheating and poor indoor air quality.
Collaboration across the industry and occupant education are key. With different systems, such as water and electric systems, it is important that all parties communicate so that we understand the brief.
It is important for regulatory bodies to understand it’s not just about ventilation; it’s about overall climate solutions. It’s not just about handling the temperature, it’s also about handling the humidity level and creating comfortable climates indoors.
The other part is, of course, about sustainability goals. The government put sustainability goals into play, and we need to make sure that we’re complying with these, not just for the developer, but manufacturers as well, to ensure that we produce the most energy efficient solution into the sector.
What technologies or solutions do you believe hold promise for addressing overheating in buildings more effectively?
Approved Document Part O provides a prescriptive approach to optimising glazing, solar shading, and natural ventilation, clearly outlining preferred solutions for keeping a building cool, all of which are important.
However, problems occur when external factors dictate that passive ventilation can’t be used to control internal temperatures. For example, if planning dictates that windows cannot be opened for risk of noise, security, or pollution, Part O lists alternative means – from acoustic façade ventilators and mechanical ventilation to mechanical cooling.
The predicted effectiveness of these solutions must be modelled in accordance with TM59 to demonstrate compliance with Part O.
Traditional methods of combating overheating often rely on air conditioning units but by merely recirculating air, these systems can reintroduce potentially harmful particulates such as dust and allergens, compromising occupants’ health and comfort and having negative effects on a building’s indoor air quality (IAQ).
©iStock | Cunaplus_M.Faba
It’s important to remember that cool air doesn’t necessarily mean fresh, clean air.
Combining ventilation with active cooling, however, not only provides cooling in the hotter months while supplying clean and fresh, filtered air into the property, but also can be used to warm the air in colder months adding to greater energy efficiency; one system that works all year round to provide an optimal and comfortable indoor climate.
Mechanical ventilation with a tempered air system can offer a better solution to overheating issues in residential properties, and can be designed in conjunction with dynamic thermal modelling.
Mechanical ventilation systems, such as Mechanical Ventilation with Heat Recovery (MVHR), often serve as the foundation for addressing overheating concerns as they are adaptable to ensure compliance with best practice guidance like CIBSE TM59.
These solutions can be seamlessly integrated into various building projects, effectively streamlining overheating concerns, delivering a ‘fit for purpose’ product for diverse construction projects and ensuring cost-effective and efficient planning and implementation.
What are the issues with retrofitting, and how can they be overcome?
Over the past few decades, the drive for more airtight buildings has been top of the priority list for the construction industry—and rightly so. Future-proofing buildings for energy efficiency is a key part of the industry’s efforts to meet net-zero targets for 2050.
Focus has been put on more sustainable and (eventually) cost-effective means to achieve this, such as better insulation, air or ground source heating, solar panels and double, if not triple glazing to prevent heat from escaping the building.
In many industry decisions to insulate tight, along with other environmental factors that impact the internal temperatures of a building, the impact on indoor air quality (IAQ) and risk of overheating increases, having a negative effect on the health and wellbeing of the occupants.
The problem we now have is that there are millions of homes in the UK that have already been brought up to modern standards in this way and are now at risk.
For example, if we look at a 1960s high rise, we didn’t think about Part O at the time, so apartments on the top floor face a higher risk of overheating than those on the ground floor.
A key solution to tackle this is installing an MVHR with a modulating bypass. These air systems optimise the overall indoor climate to create a comfortable and healthy living environment throughout the year.
In the winter months, an MVHR system extracts and filters stale air. Before leaving the house, the air passes over a heat exchange, which recovers the heat that would otherwise be lost—providing ventilation with heat recovery of up to 96%.
They then aid cooling in the warmer months as the modulating summer bypass activates when temperatures reach a pre-set level, turning off the heat recovery element and working to extract heat and humidity from the warm, humid outdoor air before fresh air enters the building. The result is a more comfortable indoor climate with a fresh air feel all year round.
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