It is widely understood that there are certain trade-offs implicit in making our homes and other buildings greener and more sustainable – whether in new-builds or via retrofitting existing structures.
Greater initial capital expenditure, in the form of higher up-front costs, translates into lower operating expenditure, in the form of decreased energy consumption and savings on bills (with the research the ABC is undertaking serving to progressively reduce that payback time). Similarly, the practical realities of installing solar panels, battery storage, heat pumps and other technologies can sometimes clash with homeowners’ aesthetic preferences.
Finding a systematic and repeatable framework for managing these tensions and minimising the trade-offs required is one of the biggest challenges facing the construction industry in its push to decarbonise our built environment.
It is critically important, of course, that we deliver a zero-carbon built environment. The industry has both a legal and ethical responsibility to act. But we also spend 90% of our time indoors, and Covid demonstrated how important our buildings can be to our health and wellbeing. Likewise, the current cost-of-living crisis has underlined how mindful we must be of promoting affordability for end users. If it’s neither affordable nor desirable to live and/or work in the new generation of buildings, all the effort to make them zero-carbon will be for naught.
For that reason, we have developed a new framework that seeks to measure and then balance the three key variables driving the decision-making process in the built environment, at every stage in a building’s lifecycle and for every stakeholder (not just its occupants). These are Comfort, Carbon and Cost.
Perhaps surprisingly, we recommend that all decision-making begins with Comfort. Crucially, in this context, that term extends to thermal comfort (i.e. being happy with the heat of the building, not just in the summer amid rising average temperatures, but also in the winter); indoor air quality (promoted by both reducing air pollutants generated internally and optimising fabric to prevent infiltration of outdoor air); visual comfort (e.g. glare-free natural light, access to outdoor views); and acoustic quality (both the type and volume of noise in the building).
Inevitably the diverse elements that comprise comfort require a combination of quantitative and qualitative measurements. These range from the WELL Building Standard that validates best practice in design and construction to promote occupier health and wellbeing; the Passivhaus and Energiesprong standards that set upper limits for overheating; polling of occupants’ thermal comfort (with the HSE advocating 80% approval rating as the lower bound for ‘reasonable comfort’); Indoor Air Quality Guidance to measure internal pollutant levels; British Standard 8223, as well as the Passivhaus standard again, for acoustic performance targets; and, in the most subjective category of visual comfort, using the Society of Light and Lighting’s methodology to maximise daylight (in an energy-efficient manner).
When it comes to Carbon, decision-makers have a narrower and more targeted focus: reducing and, in time, eliminating emissions. The most impactful ways to do this are to build nothing, identifying alternatives at the planning stage, or to build less, repurposing existing assets where possible. But in the many cases where it is necessary to embark on new building work, there are different facets to consider in quantifying the carbon impact. These span the building’s operational carbon (emissions from the use of the property) and its embodied carbon (emissions generated during its construction, maintenance and disposal).
The use of renewable energy sources and offsetting of any outstanding direct or upstream emissions can achieve net-zero operational status. However, to achieve ‘whole-life’ net-zero status (for which the RICS’s ‘Professional Statement’ acts as the reference point for a wide range of certifying bodies which include the UKGBC, RIBA and the GLA), a building must minimise both operational and embodied greenhouse gas emissions, with the balance being offset. As the national grid is gradually decarbonised, the onus is shifting onto improvements in embodied carbon. This will be possible only through a ‘circular economy’ approach that employs materials, products and systems that can repaired and reused.
Finally, decision-makers will be looking at Cost. This should be the most straightforward to assess quantitatively – but, again, there are different metrics available. Lifecycle cost (LCC) captures the initial capital cost, operational costs for maintenance, repair and upgrade and disposal costs. Whole-life cost captures all this, as well as parameters such as income and costs associated with the provisions of the construction work outside of the client costs.
What is crucial to remember when employing this framework to manage and prioritise potential trade-offs across the three different variables is that, in many cases, they are in fact strongly aligned. Most obviously, improved thermal comfort reduces carbon emissions and costs. Buildings built to minimum standards routinely deliver a massive performance gap in terms of fabric heat loss and space heating demand, meaning that an initial saving on cost ultimately damages performance across all three categories.
Where this might not be the case, however, we advocate a rebalancing of priorities. Historically, cost has been the primary driver for construction projects. This needs to change. Human health and wellbeing must be brought forward as the primary driver that simultaneously supports the UK on a journey to net zero by 2050 that is both a legal and ethical non-negotiable. If we fix a building’s comfort performance and carbon output at the necessary levels, then we can explore different price points and costing structures to find the best solution for that particular project, developer and end-user.
Achieving the construction industry’s net-zero ambitions requires greater collaboration and industry-wide buy-in from all stakeholders across the value chain. There are many areas, relating to both technical detail and high-level principle, that demand greater coordination across the industry. But the specific issue of how we can embed the principles of comfort, carbon and cost into each stage of a building’s lifecycle would be an excellent start.