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How do you eat an elephant? Tackling the existing buildings challenge one step at a time

Retrofitting By Robin Pritchett, Associate Director, Head of Building Performance UK – 14 November 2022

An elephant in a woodland opening with light shining through the trees


Head and sholders in Robin standing in the London office

Robin Pritchett

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The news earlier this year that researchers from the UK Met Office are predicting a fifty-fifty chance of average global temperatures exceeding the 1.5C Paris target in the next five years was a wake-up call for many. But as worrying as this headline may seem, exceeding the target for a single year does not mean that the long-term target cannot be achieved. It does mean, however, that it will require a concerted effort and greater focus to achieve it.

Since the Paris Agreement was signed in 2015, there has been a steady drive from the industry to lower our emissions and we are already seeing many newly designed buildings targeting net zero carbon. This is a great start, but as my colleague Marc Lynch recently pointed out in his article for MEP Middle East, when targeting net zero, the 'elephant in the room' is the challenge we face when it comes to our existing building stock.

According to the World Green Building Council’s Net Zero Carbon Roadmap, 80% of the buildings we will have in 2050 have already been built. That’s a huge challenge when you consider that the UK has almost 25 million dwellings and 1.7 million non-domestic buildings. If we are to achieve the long-term Paris targets, then we need to urgently address the retrofitting of existing buildings in order to put them on the pathway to net zero targets. This is no easy task, and the scale of the challenge seems daunting.

When faced with a challenge of this scale, I am reminded of the Saint Francis of Assisi quote, “how do you eat an elephant?”. The answer – “one bite at a time”.

To tackle this, Cundall has developed a progressive approach to net zero that helps our clients, building owners, understand where they are, where they need to go and how they get there. This starts with a portfolio analysis to identify which assets they need to target to see the greatest improvement. We then produce an asset specific roadmap for how they get there, looking at the interventions required and how they are sequenced.

When producing the roadmaps, we have adopted a seven-step methodology. This approach targets the key drivers of carbon emissions and identifies the improvement measures that have the most impact. After the plan, we design and implement the interventions. The final step is then to validate the improvements through continual review of the energy consumption data to further improve performance.

In retrofit, we are seeing a lot of focus on improving the efficiency of MEP systems, as the opportunities for passive design optimisation are limited by both the constraints of the existing building and the whole life carbon of replacing existing façade systems part way through their lifecycle. This normally includes eliminating combustion (which requires a move to heat pumps), improving the performance of ventilation systems, improved controls, reducing lighting and small power consumption. This can lead to a significant improvement in the performance of a building, but these measures alone will not get us to where we need to be by 2050.

One project we are currently designing is a large London office building originally built in 2000 with a fully glazed façade. We have improved the MEP system performance as far as possible, whilst still maintaining comfort conditions, and are on course to meet the interim 2025 UKGBC target with a potential 60% reduction in operational energy. This still leaves us short of the 2050 targets by quite some margin. The image below shows the performance of the existing and refurbished building against the various interim and 2050 targets.

The remaining reduction required in energy consumption will either need to be met by changing the façade design, with all the associated carbon emissions, or by changes in occupant behaviour to accept higher temperatures in summer and lower temperatures in winter.

Both of these pose significant challenges, be it from a planning perspective and disruption to day-to day-activities or from the communication challenge to occupiers who need to be part of the conversation about how their decisions impact on the wider environment.

As engineers, we strongly believe that net zero needs a technical solution and that we are best placed to provide it. We have adopted a progressive approach to net zero that eats the problem “one bite at a time”, and eventually removes the elephant in the room. However, MEP improvements can only take us so far and if we are to succeed in achieving the various net zero targets across the globe then the entire construction industry will need to come together to address the challenges.