As an industry we have known about overheating for years but probably haven’t taken it seriously enough. From anecdotal conversations referencing buildings where summertime temperatures topped 40 degrees to discussions with MEP engineers about insulated heating pipe work and how we can combine smoke ventilation with fresh air supply, we have had the luxury of playing around the edges. But with the incoming Part O of Building Regulations, we are going to have to be more determined about designing out overheating.
By Craig Sheach, Partner at PRP
In the same way that climate change has affected the ground floor environment with increased flood levels from revised climate data, updated weather maps means overheating has quietly become a big issue. Designing to resolve it will be a challenge for the industry as a whole – technically, ethically and economically – however, it represents a more unique challenge to the Build to Rent and rental/investment segment.
Build to Rent relies on its location. Strong local facilities and wider transport connectivity generally mean town centres or dense urban environments are favoured. With these locations can come acute environmental challenges such as Urban Heat Island effect, increased acoustics and poor air quality; the latter two, the sworn enemy of the openable window. And herein lies the issue. Our research is suggesting that in order to comply with the new Part O, especially in bedrooms, the air volume to cool ambient levels has a greater effect than managing solar gain. How can we cool the occupants by passive means if you can’t open windows at night because the outside environment is untenable?
The starting point must always be exploring passive measures because we need to minimise energy consumption to reduce carbon as well as running costs. That means exploring building form, orientation, façade specific shading, fabric efficiency, glazing proportions and their properties (g-values), thermal mass, etc… all of which are critical in the fight against unwanted solar gains in summer. But, they cannot replace the need of providing passive ventilation and the air coming from openable windows. Acoustic side vents can work to some degree, but beyond this, there are limited options if the windows can only open by a few degrees because it is too noisy outside.
Part O encourages dual aspect living but only defines this as through-apartments, ignoring corner homes. The implication to viability of this is significant, increasing the number of cores, or using deck access, and reducing the depth of blocks. All are laudable aspirations but whether viability models or market sentiment can handle these approaches only time will tell.
So where does that leave us but to look at active solutions. Enhancing mechanical ventilation with greater flow, adding cooling modules and even full AC is contrary to what we are trying to achieve – lower energy usage and carbon reduction. In a sector where carbon footprint is important for CSR and institution ethics, and where environmental credentials matter to the very demographic that wants to, or needs to, rent, these active systems surely cannot be the way forward, or at least the default starting point.
Compliance now also doesn’t mean overheating will not be an issue in the future. A Build to Sell development worries about compliance at the point of sale. A Build to Rent investor holds the asset for decades. An out of date approach to overheating could start to increase churn later on in the lifecycle, increasing voids and decreasing health and wellbeing of their stewarded communities. Should Build to Rent developments be looking to greater standards than just minimal compliance, or greater flexibility, to future proof the buildings as post fixing solutions is costly and technically challenging.
Why is all this relevant? Simplistically Build to Rent renters vote with their feet. If you own a house, on hot days, you buy fans, AC units, shutters and you grumble but essentially put up with it because of your ownership lock in. On a rental block, residents will move at the end of their contracts if they get too hot, because it’s easy to do so. How to deal with overheating then becomes a point of competition between developments and potentially a USP.
In the end, the new Part O points to a paradigm shift in how we design buildings to deal with climate change and it certainly looks like it can’t be business as usual, especially for Build to Rent developments. Passive design should absolutely be our starting point, but will we end up with a technological solution in the end?