Is there a carbon case for demolition?

The legacy of good intentions

Agentia co-founder Gerry O’Brien reflects that well-intentioned but misplaced actions, implemented successively, have led humanity to its current climate and biodiversity emergency. He acknowledges that many of these good intentions originated with engineers.

For most of these well-intentioned actions, the focus, and the limit of consideration, was the immediate impact. Whether reducing mortality through public health engineering (such as clean water and sanitation), cutting travel times with steam locomotives, or propelling prosperity through aviation, the immediate benefits were obvious; the wider consequences were not.

“I’m not sure what it would mean for society today had humanity pondered, ‘This clean water stuff is great, but if we live longer, perhaps we should create new humans at an adjusted rate?’ Would there be seven billion of us? How different would the challenges be for the class of 2025? The reality, however, is that there are seven billion people. In the UK alone, there are around 35 million cars, with 2.4% of the country's surface area dedicated to them. That amounts to a staggering 3,694 km² of hard surfacing. On average, 11% of urban land is devoted to cars and trains, which is 1.8 times more land than is typically occupied by homes.

We did these things to improve lives, yet the consequences now threaten to reduce our quality of life. The impact of the greenhouse gases we have pumped into the atmosphere is returning to demonstrate the ‘law of unintended consequences’.

We must now heed these lessons. We have studied the impacts of our built environment for decades and know, without doubt, that urban sprawl is catastrophic for land use, ecology, and biodiversity. We know we can create cities that support high-quality living while requiring far fewer resources to sustain us, thereby releasing less CO2 into the atmosphere.

The transport carbon equation

“I found it curious when Westminster Council dictated that for a retrofit project to gain planning permission, it must retain over 50% of the building’s fabric. While I understand their aim, the move effectively prioritises the building fabric, regardless of its quality or suitability, over the site’s societal potential. It likely means that, in many circumstances, we will build whatever we need in other locations, resulting in a poorer global outcome.”

O’Brien explains why this matters: “Historically, calculations of the CO2 released by a building have focused on construction and operational carbon. However, this often misses the largest element: the CO2 produced by users commuting to and from that building.”

The figures backing this are stark. Imagine an office constructed to LETI carbon targets of 550kg/m² with a 10m² occupancy per person. This means one workstation releases 5,500kg of CO2. If this workstation is in Westminster and accessible via zero-emission transit, the transit carbon is negligible. However, if we build the same workstation where access relies on cars, the picture changes. An average car, travelling an average 20-mile commute (based on 180g/km and a 47-week working year), produces 2,700kg CO2e annually. This means commuting doubles the carbon footprint in just two years. Put another way, between now and 2050, that commute will add 73,000kg CO2e to the atmosphere, around 13 times more than if the office had been built in Westminster or near a zero-carbon transit hub.

O’Brien concedes that whilst the maths is basic, the substance of the argument holds

Prioritising societal need

Having worked on projects of all scales across the UK and globally, O’Brien insists there is no ‘one size fits all’ solution. For years, he has argued that we must “Think more, use less!” and study a building’s impact across multiple boundaries: the site, the neighbourhood, the city, and the nation. Against this backdrop, O’Brien warns that rigid reuse targets risk constraining density in precisely the places where high-intensity development offers the lowest transport emissions.

“We must start with societal need,” he argues, “and only then determine what should be retained, following a holistic assessment of the carbon cost of the building’s existence; this must include carbon released through transit.” If we do not need it, we should not build it. But if society dictates a necessity, we must ensure we do it in the best possible way.

This means that new buildings are not dead. It supports the view that, in certain circumstances, we must knock things down to build back better.

Examples of efficient land use

Land use is a critical consideration. Research shows that land returned to the wild, absorbs carbon with great efficiency. Instead of building on greenfield land, we must maximise brownfield opportunities within our towns and cities.

O'Brien has encountered situations where the societal potential of a site outweighed the constraints of retaining the existing structure. At 99 Bishopsgate, the proposed building for Brookfield Properties uses the site to its fullest extent, more than tripling the net office floor area. This aligns completely with the City of London's strategy to provide 1.2 million m² of office space and create 66,000 new jobs by 2032. Realising this benefit required dismantling most of the existing building.

In contrast, the proposed development at St Thomas' Yard was designed to align the new building's massing with the load-bearing limits of the existing structure. This approach maximised reuse while delivering the greatest floor area within the planning envelope.

O’Brien’s experience on these projects underscores his assertion that a ‘one size fits all’ approach does not make sense. Instead, we must make the effort to thoroughly understand a building's holistic impact in the context of the climate emergency.

Think more, use less!