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Small firms can measure carbon too

Ben Hair

Cost needn’t deter smaller practices from calculating the carbon of their designs. Ben Hair explains Knox Bhavan’s approach

The carbon dial from KBe tool gives a snapshot of the carbon health of a building.
The carbon dial from KBe tool gives a snapshot of the carbon health of a building. Credit: Knox Bhavan Architects

Smaller practices often don’t have the resources of larger practices to devote to understanding their projects’ embodied carbon. Carbon tools have pushed the conversation forward, but can be difficult to apply to smaller buildings.And there’s a fear of what carbon calculations might reveal; architects can worry that they’re hiding carbon-heavy skeletons in their portfolio closets. 

But understanding carbon can be a positive process. We began developing KBe by auditing our built projects. We learnt where things could be better, but also found affirmation of our instincts as architects. Designing with local self-finishing materials and striving for efficient, elegant structures led to buildings that weren’t that high in embodied carbon.

Carbon literacy can be a barrier too. 

It takes time to get your head around carbon and really understand what sustainability means. Our definitions evolve constantly. Just 18 months ago I thought we were aiming for net zero buildings. Now I’d say there’s no such thing as a carbon neutral building – though we should keep working towards it. 

Three-pronged approach
The method we have developed comprises three steps: measure, communicate, reduce. Measure is where the data comes in, split into two inputs: quantities and carbon factors. We measure the quantity of material from schedules of works, tender packages or BIM models. The integration with 3D modelling can make the whole process more seamless to work out how much steel, timber, concrete are in the design.

Carbon factors are more complex, and we use a combination of the ICE database and product-specific EPDs to get started. For harder to measure items, lights and cabling for example, we’ll do an estimate based on  LETI guidance.

Combining the quantities with the carbon factors gives us the embodied carbon of a building at a given stage. To communicate that, we’ve developed the KBe carbon dial, which is a snapshot of the carbon health of a building.

Orange segments show embodied carbon, dialling clockwise about the centre. Green dials counter-clockwise, representing the sequestered carbon. Yellow in the centre shows embodied carbon in existing structures that might be retained or demolished. 

Routes to retrofit
The idea is to encourage balance in carbon positive and negative materials. By being clear about what is demolished and retained, we hope to beat the drum for retrofit-first. We also translate carbon emissions into understandable metrics like equivalent London bus rides or flights to Sydney to encourage engagement and increase access to the conversation.

With the emissions of each building element communicated in the dial we can assess where carbon can be reduced or which design option performs best. The KBe dial shows us where to focus our time and energy; the floors might be performing badly for example, what can we do about it? The roof looks really light carbon-wise; let’s find out why.

At RIBA stage 0-3 we can give quite broad figures, that reflect the early stage of design. This is a great point to set carbon benchmarks for the project. You’d do it for area schedules and cost plans, so why not set a budget for carbon? It’s a great way to bring the client with you.

At technical design and tender documents we can tighten the analysis to measure how the designed building stacks up against the carbon benchmarks. You can even have a value engineering exercise to cut carbon, not cost.

Finally, a post-occupancy exercise measures embodied carbon as built and projects the building’s whole life carbon (so far we’ve been more concerned with ‘as built’). Most of our analysis to date has been of this nature as we’ve developed the process with our completed projects.

It gives us a new challenge and a new metric to measure the success of our buildings and to discuss these with clients. Everyone wants to be sustainable, but the numbers and dial allow us to show clients what one brick might mean compared to another and how choices have an impact far beyond the site boundary. 

We hope to get more small practices involved in our research over the coming months. In collaboration, small practices can make a massive difference. 

KBe has also helped us to see how construction is changing. Our older projects seem to quite light in carbon terms compared to more recent ones. The simple reason for that is that we put more stuff into buildings today than we did 30 years ago. Insulation has an embodied carbon footprint: as u-values go down operational carbon should too, but embodied carbon also goes up. There’s a balance to be struck there and we’re getting better at understanding where that balance lies.

KBe began as an audit of our built projects. That included March House and Threefold House – both won RIBA awards this year while March House won the Sustainability Award too. We’re using it in one form or another on all our projects. It’s a constant feedback loop: the projects help us develop KBe; KBe then helps us develop the projects, and it rolls on like that. It’s never going to be finished. KBe is probably never going to be 100% accurate and I don’t think buildings can ever be considered totally carbon neutral, but they’re moving in the right direction. It’s the direction that’s important.

There’s no silver bullet. As with everything else in construction, sustainable design is the result of countless tiny decisions that combine to create something. There’s no one thing that will make it happen on its own.

There’s also more nuance in sustainability than I appreciated before we began all of this. On the house in Peckham we were deciding between insulation made of cork or recycled wood-fibre. The cork would have been much better performing in embodied carbon terms but it was a virgin material. The wood-fibre on the other hand was made of waste materials that would be in landfill if not made into insulation, but as a result less carbon was sequestered in its lifecycle. The question of which material is more sustainable to use is more complex that it first looks.

The main lesson though is to give it a go. You don’t have to work it out for a whole building, but you can see if you can work out what difference the brick makes in embodied carbon terms. Or what the carbon associated with the transport of windows from here or from there is.

While small practices have modest resources as individuals, there is huge potential in their strength of number and their collective knowledge base. The majority (around 80%) of practices in the UK have fewer than 10 members of staff. We’re hoping to tap into that knowledge base in the next stage of KBe’s development, inviting other practices to contribute to the research.

Ben Hair is sustainability lead at Knox Bhavan





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