Sustainability Series: Week 3, Energy
Webinar: Energy efficient homes - some contemporary solutions
Recorded: 25 October 2022
This webinar presents two recent exemplary housing developments: Max Fordham House and Howgate Close, each the result of years of experience and design development focusing on reducing the energy demand of buildings. A recording of this event is available in the on-demand hub.
Blog: The case for passive solar design in 2022
Although the current version of Part L (2021 edition) only came into force back in June, attention is already turning to the next update, which is just a couple of years away. The next set of changes to Part L will coincide with the anticipated 2025 Future Homes and Buildings Regulations, which it will underpin. These Regulations will introduce even higher levels of energy efficiency and lower-carbon heating, ensuring an even deeper cut in the carbon emissions from new homes, going further than the 31% now required by Part L.
In contrast to previous Part L updates, the 2021 edition focuses more keenly on the performance of the services and building systems in order to meet the new performance targets. This shift in emphasis partly reflects the progress that has already been made in improving fabric energy efficiency, making a switch to low or zero-carbon heating systems the next logical step. It also aligns with the guiding objective of ensuring new homes are zero carbon ready; a key objective of Part L going forward.
However, it would be wrong to think there is not much more scope for improving fabric performance. Whilst it is true that the law of diminishing returns applies when more insulation is added, there is another aspect of fabric energy efficiency that still has much to offer, that is the use of Passive Solar Design (PSD) to reduce a home’s space heating load.
PSD involves optimising the orientation, window size/location and use of floors and walls with thermal mass, to enable solar gains through south facing windows to be stored and then released back into the room later in the day as the temperature drops. Since the sun is at a low angle during the winter months, it can shine under south facing window overhangs, which provide shade from the higher angle summer sun, reducing the potential for overheating. Given that that PSD is a very old and well established technique, it is perhaps surprising that it’s not more widely used in the UK.
To explain this, I think you probably have to go back to the 1970s when, following the last big energy crisis, there was a lot of interest in PSD and uptake steadily increased, peaking in the mid 80s. The DTI also invested £6 million in promoting PSD in the early 1990s, from which came some useful design guides including: Planning for passive solar design, and Passive solar schools. Despite this, there are several likely reasons that it never became part of mainstream housing design.
The first of these is energy prices, which in real terms steadily declined during the 1990s. There was also the eventual realisation that the priority should be to firstly improve insulation standards, which was the low hanging fruit at that time. The growing popularity of conservatories did not help either; which PSD regarded as a form of sunspace or thermal buffer. However, in practice these mostly ended up being built and used without regard to PSD, with heating often installed for greater utility.
Fast forward to today and the case for PSD is stronger; energy is no longer cheap, and fabric performance is considerably better. However, a number of barriers still remain including SAP, which continues to set performance targets based on a ‘notional building’ of the same shape and orientation as the design being evaluated i.e. it does not encourage optimisation of the building form and orientation to save energy.
Setting targets based on a notional dwelling approach may be preferred by many developers/designers as it permits greater flexibility in terms of site layout and building design, which is another reason for the lack of uptake in the past. The implications of PSD for site layout is probably also why the idea of moving away from the notional building approach was not taken further when suggested in a SAP consultation a few years ago. Perhaps the next major SAP update (SAP 11) and forthcoming changes to Part L will revisit this issue given the pressing need to reduce our energy use, much of which is for space heating.
In the meantime, it is encouraging to see that those helping shape these future revisions are talking about the need to encourage efficient building form and the negative impact of using low g-values for glazing, which reduces passive solar gains in the heating season. There is also an acknowledgement in the new Part O overheating regulations, that “Reducing summer overheating by limiting window size will impact winter solar gains and therefore increase the need for space heating.” In broad terms, the issue could be regarded as a question of favouring site layout/density or greater passive performance; perhaps a compromise between the two is the answer. There is less of a conflict with self-build homes and smaller developments, where PSD continues to be more commonly found, for example in Passivhaus projects, where it is an integral part of the design approach. Examples of PSD include:
Like Part L, the development of SAP 11 will be aligned with the 2025 Future Homes Regulations. To see what SAP 11 is likely to include it is worth looking at the report published by BRE and Robust Details, which explores the likely mainstream technologies that will need to be considered. Work on SAP11 was announced back in May by the BRE, who described it as “a root and branch review of the existing methodology to create a new version that is better suited to modern and dynamic technologies which will help decarbonise the UK’s housing stock, such as heat pumps, renewables, storage technologies and smart control devices”.
Thermal mass can be used as one of these storage technologies, opening up new ways in which medium and heavyweight construction materials such as concrete can play a more active part in helping deliver net zero carbon homes. The use of thermal mass as a storage technology is the subject of another article, which you can read about here. This new application sits alongside its more traditional roles of helping mitigate overheating and as integral part of PSD. So, as a building concept, use of thermal mass is perhaps more relevant today than ever.
Written by Tom De Saulles, Building Physicist, The Concrete Centre
Other resources
For further guidance related to design to improve energy efficiency using concrete and masonry, please refer to: