Part O of the building regulations is relatively new, having come into effect in June 2022. Part O requires specifiers to incorporate measures that mitigate the risk of overheating in dwellings and other residential buildings. Part O seeks to achieve the mitigation of overheating by limiting unwanted solar gains during the summer months and by ensuring there are adequate means to remove excess heat from the indoor environment.
A number of factors can contribute to overheating, but there are also several design strategies that help maintain comfortable internal temperatures and support compliance with Part O. One such approach is using the building fabric itself as a thermal buffer through the use of wood fibre insulation.
In this blog, we explore the growing issue of overheating and the reasons behind its increasing prevalence. We also examine how the beneficial properties of wood fibre insulation can be considered by specifiers and developers. It limits internal heat gains using passive cooling to help reduce the need for air conditioning to manage excess heat within the home.
What issues does Part O look to address for homeowners?
Part O[1] looks to prevent the situation from arising where internal temperatures rise to uncomfortable levels for homeowners.
While there is no officially defined upper indoor temperature limit for health, 26 °C is referenced in several health policy documents such as the NHS Heatwave Plan for England[2]. It is also the temperature at which openings are assumed to be fully open in CIBSE TM59 dynamic thermal modelling[3], which can be used to demonstrate regulatory compliance, as outlined in Section 2.6 of Part O.
Prolonged exposure to high temperatures can have harmful effects on occupants, with the level of risk varying according to age and overall health. Older people, young children and infants are particularly vulnerable to high temperatures due to a reduced ability to regulate body temperature and recognise thirst. Risk is further increased by chronic health conditions, mobility or mental health issues, obesity and social isolation.
Exposure to heat can lead to a range of health effects, from mild conditions such as dehydration, heat rashes and dizziness to more serious outcomes including reduced concentration, mental health impacts, heat exhaustion and potentially life-threatening heat stroke[4].
Why is the importance of Part O likely to grow?
The importance of Part O will grow due to the increasing effects of climate change. With hotter summers, the risks of overheating are increasing[5]. In the Committee for Climate Change report[6], it states that under current UK weather conditions, 50% of existing UK homes will suffer from overheating risk. If global temperatures were to rise by 2°C, this number would rise to 90%.
Part O requires housing developers to address overheating through passive measures, rather than relying on energy-intensive solutions like air conditioning. Without effective passive strategies, households may face summer fuel poverty[7], where they are unable to afford to run air conditioning units to cool their homes.
Why do the properties of wood fibre insulation help compliance with Part O and support occupant comfort?
Wood fibre Insulation helps to slow down the passage of heat no matter which direction it takes. It can assist with keeping the heat in during the winter and keeping the heat outside the house on hot summer days, to support occupant comfort throughout the year.
The extent to which insulation can mitigate the effects of overheating will depend on the type of insulation. Using wood fibre insulation adds thermal mass to the walls and roofs, helping them to keep the building cooler in the summer.
However, wood fibre insulation can do more than just increase thermal mass, as its ideal combination of high density, high heat storage capacity and low thermal conductivity can help significantly with reducing the risks of summer overheating.
Wood fibre insulation combines high density, high heat storage capacity and low thermal conductivity to significantly help reduce the risk of summer overheating. These properties enable the insulation to absorb and retain heat during the day, slowing its transfer into internal spaces. This creates a time delay, so peak solar heat does not immediately affect indoor temperatures.
Importantly, these characteristics can be calculated and expressed as part of a building’s thermal performance. In much the same way that U-values measure heat transfer during winter, summer performance can be quantified using parameters such as thermal diffusivity and time delay.
Thermal diffusivity combines density, specific heat capacity and thermal conductivity to indicate how quickly a material responds to temperature changes. A lower diffusivity means heat moves more slowly, creating a longer time lag between external temperature peaks and internal temperature rise. By incorporating these calculations into design, specifiers can compare materials not only for winter efficiency but also for their ability to moderate summer heat.
While reducing the risk of overheating in homes typically requires a combination of strategies, such as limiting solar gain and creating well-designed ventilation paths, designing the building fabric to act as a heat buffer can make a significant difference.
Using wood fibre insulation helps housebuilders provide dwellings with a fabric that can help to maintain comfortable internal temperatures for their occupants and support compliance with Part O of the building regs.
Where can I find out more information about wood fibre insulation?
STEICO offers a range of wood fibre insulation boards and batts that are characterised by a higher raw density (volume weight) than many conventional insulating materials.
This means that they can offer much greater resistance to heat radiation due to their higher heat storage capacity. The heat of the day is buffered in the insulation material until the cooler evening hours. Independent studies show that the days with unpleasantly high indoor temperatures can be almost halved by using wood fibre insulation materials.
To enquire about using wood fibre insulation to support the mitigation of overheating on your next project contact us and we will be happy to help.