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How much extra does it cost to make a building net zero carbon?

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Photo by Chris Gray on Unsplash

What are the real-world implications for achieving new net zero buildings? How can new buildings be designed to reach net zero performance targets and what effect does this have on cost?

These are the questions researchers for the UK Green Building Council set out to answer with a deep dive into the implications for two real-life buildings at design stage: one residential block and one office building.

The idea was to deliver the same building that had already won planning approval (in terms of overall volume, external massing, site conditions), but to change any of the other design parameters (such as structure, HVAC system, tenant requirements etc.) in order to achieve, or get as close to achieving, the net zero performance targets.

These targets cover embodied and operational carbon. The researchers looked at the base designs and produced two alternative designs for each, one aimed at meeting 2025 net zero performance targets and one aimed at more ambitious 2030 targets.

According to chief executive officer at UKGBC: “This study provides long-awaited evidence that building today to the standards of energy and carbon efficiency required by 2025 doesn’t have to cost a fortune and is likely to be offset by enhanced value.”

What are the net zero targets?

They are based on:

1. The Royal Institute of British Architects (RIBA)’s 2030 Climate Challenge
2. The London Energy Transformation Initiative (LETI)’s Climate Emergency Design Guide, and
3. The UK Green Building Council (UKGBC)’s Net Zero Carbon Buildings: A framework definition and Energy Performance Targets for Offices.

And are summarised in this table:

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Some net zero targets could not be achieved because they required radical changes to the original building design.

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Measures taken

The ambitious 2030 results could be achieved with the following measures:

For the office

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Section through the office development

Replacing the steel and concrete in the office’s structure with a fully timber structure along with the removal of a concrete basement reduced the total upfront carbon by 39 per cent, compared to the baseline. However, the larger-sized timber beams and columns did result in one floor being lost to maintain the same building height, which would alter the building’s value.

By relaxing the internal comfort conditions for the office’s occupants a little, the heating and cooling demand could be halved. This meant using openable windows for passive cooling in the spring and autumn.

Finally, by not installing a suspended ceiling, embodied carbon was cut by 13 per cent. Furthermore, outsourcing servers for the computers achieved a 78 per cent decrease in IT energy usage, but of course these emissions still exist and so must be offset.

For the apartment block

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Artist’s impression of the original residential design

Again, replacing the concrete structure in the tower block with a timber frame (beams, decking and columns) helped reduce total upfront carbon by 21 per cent. But because of the increased depth of the beams, two floors had to be removed to maintain the overall building height, again affecting the value.

To cut heat loss and cooling demand, the amount of glazing was reduced from 51 per cent to 29 per cent by reducing bedroom window sizes and removing bedroom balconies. Triple glazing and reducing the wall u-value also helped.

Substituting an air source heat pump for the gas boiler significantly reduced the operational energy demand. Around half of the final energy demand in the ambitious 2030 scenario now comes from unregulated loads.

What was the effect on cost?

To calculate the effect on cost, the team took into account current market trends, such as investor pressure through the Task Force on Climate-related Financial Disclosure, stranded asset risks, corporate ESG drivers, and increasing occupier interest in net zero.

They worked out that the extra cost for the office was 6.2 per cent (for the medium 2025 goals) and 8-17 per cent (for the advanced 2030 goal) and for the residential 3.5 per cent and 5.3 per cent respectively.

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These extra costs would probably be offset by increased rents, lower tenancy void periods, lower offsetting costs, and lower operating/lifecycle costs.

They conclude that the net zero targets for 2030 are substantially more demanding and the marketplace is not yet geared up to delivering them at scale.

To tackle this they believe that governments need to guarantee certainty with a long-term consistent regulatory pathway that increasingly tightens standards so the supply chain is motivated to invest and innovate and costs will then come down.

“Yet again, we are reminded that more visionary policy-making and bold industry leadership must go hand in hand in the quest for net zero carbon outcomes,” the UK GBCA’s Julie Hirigoyen said.

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Written by David Thorpe
David Thorpe is the author of the books The ‘One Planet’ Life and the new ‘One Planet’ Cities. He lives in the UK.

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