WHY CARBON CALCULATIONS FAIL TO REFLECT THE REALITIES OF URBAN ENVIRONMENTS

Carbon-conscious design is a vital plank in addressing environmental impact, but reducing carbon alone is not enough. True long-term value in building design comes from balancing carbon with critical factors that give it social impact.

Quality, usability, productive space, aesthetics, and durability all determine the value of the carbon used in delivering the built environment. The industry needs a more nuanced, integrated approach, particularly in structural engineering, to create buildings that are not only low carbon but also adaptable, resilient, and future-ready- creating spaces that are productively used and remain relevant.  

Carbon use does matter

The built environment is responsible for nearly 40% of global carbon emissions- of which structures accounts for up to 50% (World Green Building Council). Structural engineering sits at the heart of the climate challenge.

Encouragingly, the construction industry has already made significant strides in carbon reduction. Progress has been driven by clear regulatory frameworks and guidance such as London Energy Transformation Initiative, SCORs, British Council for Office Guidance and more. Ambitious carbon targets have been set along with the guidance and resources to support the reduction of both embodied and operational carbon. These frameworks have helped to track, regulate and benchmark low carbon design, but they draw focus to carbon at the expense of other considerations, which are potentially less measured.

Existing guidance

	Focus/Guidance	Key Contributions/Targets	Challenges/Notes
LETI (London Energy Transformation Initiative)	Net Zero Carbon buildings; Whole-life carbon; Embodied & operational carbon targets for 2030	LETI 2030 Carbon Targets by building typology	Calls for consistent carbon metrics across the industry Emphasises the need for early-stage decision-making in design
SCORS (Structural Carbon Rating Scheme) by IStructE	Rating scheme for embodied carbon; Track performance improvements and set 2030 targets; structural engineer focused		Used to clearly communicate the implications of design decisions to wider design and client team. Meaning is assigned to a green A+ rating, or a red F rating, facilitating conversations around embodied carbon during the design process. Using science-based targets they provide a more stringent framework- focussed on structures.
BCO (British Council for Offices) guidance	Commercial office design; Energy performance; Space efficiency; Embodied & operational carbon reduction	New guidance recommends:  -10m² per person (up from 8m²) to reduce over-specifying services - BREEAM ‘Excellent’ and 5-Star NABERS UK as minimum targets for new buildings - Net Zero Carbon prioritised, with aspirational targets for operational and embodied carbon - Focus on energy efficiency: increased outdoor air, efficient lighting, reduced power/cooling loads, high-performance facades - Greater flexibility in structural spans; 6m and 7.5m grids introduced to reduce embodied carbon	Places major focus on design team requirements for long term flexibility and carbon-conscious design.
UK NZCBS (Net Zero Carbon Building Standard) PILOT VERSION	A cross-industry standards to robustly determine whether built assets (existing and new buildings) in the UK are Net Zero Carbon and in line with the UK’s climate targets. The standard aims to be ambitious but also achievable and science-led.	Embodied carbon limits for new works and retrofit works for various types of building have been set every year from 2025 to 2050. For example, New Works Offices has an embodied carbon limit in 2030 of 470 kgCO2e/m2GIA and reduced to 40 kgCO2e/m2GIA for 2050. (refer to the following document for all limits: 6ea7ba_1ef36b6835de46668f2ad8b589ff1b93.pdf)	The pilot version is live and being used in industry. Collection, analysis and feedback from the pilot testing will be used to develop the Version 1 of the standard which is currently set to launch in late 2025, with the aim to eventually supersede other documents listed above.
Part Z (Proposed Document Z)	A proof of concept of the regulation needed in the UK to ensure embodied carbon is assessed on all projects and therefore it is an industry-proposed amendment to the Building Regulations 2010.	The proposal includes setting out relevant legislation, whole life carbon requirements for projects with a gross internal area of 1000m3 or that creates more than x10 dwellings and setting limits for upfront embodied carbon. Part Z	This is an existing industry proposal and not yet part of the building regulations.

What is the weight of carbon?

How much weight should carbon carry in our decision-making process? For example, where green and blue roofs add to the embodied carbon that supports them, are they always the right thing to do? Where preserving townscape requires carbon intensive setbacks in the structure, should architectural heritage and urban form override the need to minimise carbon? The challenge of balancing the significance of carbon values against other aspects of the project is a tough one.

To fully understand a building's value, we must consider more than just carbon emissions. Rather than allowing carbon values to determine design decisions we should be considering carbon among other factors to create long lasting and meaningful value; including:

1.Quality

Since the pandemic, the way people use office spaces has shifted. While hybrid work is here to stay, demand for high-quality spaces is growing- with high quality being defined as location, amenity, presence and ESG performance.

Even though office attendance has now stabilised at around 30% below pre-pandemic levels, we are continuing to see an increase in the demand for Grade A buildings. Data shows that 86% of office space leased in the first quarter of 2025 was in Grade A buildings - up from 80% in 2024 (Knight Frank, Demand for London Offices Hits Post-Financial Crisis High). Tenants are prioritising environments that attract and retain talent, support collaboration, and justify the commute. Quality matters more than ever; and whilst design quality doesn’t always equate to carbon, factors like large amenity facilities and generous spaces often can.

2.Usability

Buildings must be functional and adaptable to the evolving needs of their users. Post-pandemic strategies increasingly favour flexible, centralised environments that support hybrid work. A user-centred design approach can help maximise operational efficiency and ensure that spaces remain relevant over time. Structures with longer spans enable adaptability, but with a punitive impact on the embodied carbon, moving support spaces like plant rooms and cycling facilities to basements improves the ground floor functionality, but again at a high carbon cost.

3.Productivity

While productivity is challenging to measure and quantify precisely, data shows that well-designed, well-managed office spaces can boost productivity by 2–3% (British Council for Offices).

(Images Source: British Council for Offices)

Environmental factors such as lighting, noise, temperature, and air quality all play a critical role and should be optimised even in existing buildings.  Spatial quality and adaptability can be harder to quantify due to them being unique to each building. We believe that when we assess the amount of carbon used to deliver an office, how productive the space that carbon creates should be a fundamental factor in that assessment. The productivity is fundamentally what we are utilising the carbon for.

4.Urban Quality

Aesthetic appeal can also enhance the public realm and sense of place, creating spaces that foster wellbeing and community. By prioritising amenity and shared environments, buildings can support urban densification and encourage greater use of existing infrastructure. These qualities not only attract tenants but also improve retention and rental yields for clients and developers.

These carbon investments keep cities attractive, with evidence supporting that cities produce less carbon per capita (circa 4 tonnes per capita as opposed to circa 6 tonnes outside- source BEIS 2020). There is also evidence that cities become more creative and more effective as they grow. Key considerations in ensuring our cities need provide attractive places as a part of the battle against climate change.

5.Durability

A structure that is built to last and adapt to future needs is more sustainable in the long run. When considering embodied carbon, it is essential to weigh it against a building’s durability, flexibility, and potential for reuse or repurposing. We currently use the materials design life as a fundamental part of that assessment, not how long the building will remain relevant and productive. This seems to be a fundamental flaw in the assessment process.

True value lies in how buildings serve people, adapt to change, and perform over time. As designers of the built environment, we must balance carbon considerations with quality, usability, productivity, aesthetics, and durability to create spaces that are not only sustainable, but meaningful and future ready.

The problem with scorecards

One major issue is that industry decision-making is often driven by carbon scorecards and frameworks that overlook broader performance outcomes. As a result, we sometimes see low-carbon developments move forward solely because they meet technical carbon benchmarks, even if they fall short in other critical areas such as adaptability or social value.

High-profile projects delivered pre-embodied carbon assessment- like Bloomberg’s London HQ or Google’s King’s Cross campus- have set benchmarks for buildings in operation- delivering flexible and adaptable spaces, but they are also extremely carbon intensive. These projects highlight the challenge of keeping our built environment attractive with a carbon cost that is warranted.

In contrast, Marks & Spencer’s recent decision to demolish and rebuild its Oxford Street store, rather than refurbish it, raised serious debate. Experts argued the embodied carbon of demolition and construction against the potential benefits of new construction, showing how current frameworks don’t necessarily create clarity.

Policy inconsistencies and gaps

We also face inconsistency in how carbon is assessed and applied across the country and even between different boroughs. Some local authorities have progressive guidance- such as the City of London- while others have yet to define their view- making it difficult to apply best practice at scale.

Current policies do not sufficiently incorporate whole life value or offer clear direction on how to trade off carbon against other critical metrics.

We believe there is a need for a more standardised and nuanced approach, led by policymakers, that integrates carbon with other performance criteria, including quality of space, adaptability, longevity, and user outcomes. As we move toward regenerative design we need to create more holistic assessments which incorporate social impact.

How does this relate to structural engineering and building design?

Structural engineering plays a fundamental role in delivering buildings that balance carbon with long-term value. The early design phase, particularly optioneering, is where the biggest opportunities lie.

1.Retrofit vs. New build

Retrofit is usually the lower-carbon solution and London Structures Lab support a retrofit first approach as indicated below in the assessment of an office building in Southwark, whereby the full demolition and rebuild had much higher embodied carbon value than option which looked at heavy retrofit. However, it is not always the best option for creating productive and highly occupied buildings. In some cases, retrofit has led to compromised performance or constrained adaptability. A more layered approach would enable a more even assessment of the factors - evaluating carbon alongside quality, lifecycle cost, and spatial potential.

Option 1 Embodied Carbon = 270kgCO2e/m²

Option 2 Embodied Carbon = 185kgCO2e/m²

2.Designing for flexibility

Creating soft spots or flexible zones within buildings allows spaces to evolve without major interventions. This can reduce future embodied carbon while supporting changing tenant needs. A good example is seen on 124 Theobalds Road, which incorporates a flexible floor strategy in its front extension. The design allows every other floor to be easily removed in the future, creating double-height spaces within the permitted fire strategy. Edge columns are designed to remain stable when these flexible floors are removed, enabling long-term adaptability without major structural intervention.

3.Disassembly

Designing with demountable elements allows for future disassembly, reuse, and adaptation. This shift thinking from permanence to circularity, embedding resilience into the structure itself. Disassembly and reconfiguration of elements within an existing structure can minimise the need for new materials and therefore the associated embodied carbon- as shown by Bedfont Lakes, an workspace in Feltham. As the original building was designed by Michael Hopkins in the 1990’s it employed the high-tech aesthetic of exposed structure as the architecture. This meant the structure had not just commercial and carbon value, it also had cultural value. Dismantling, and reconfiguring the plant room on the roof to create new workspace made sense on all metrics.

This isn’t always the case and designing for disassembly can clash with the ethos of designing lasting structures and frequently demands higher initial carbon and financial investment. For example, steel beams designed none compositely require more steel (and therefore more carbon) but are more easily demountable and more circular. Welded connections can create greater fixity and reduce material usage but create more wastage during demolition. If this carbon spent on future flexibility isn’t used it is carbon wasted.

3.Regenerative materials

Material selection is crucial. The use of low-carbon, responsibly sourced, and bio-based materials can reduce upfront carbon and help minimise biodiversity loss. Structural systems and materials should always be evaluated not just for strength and efficiency, but also for their environmental impact at every stage of the material supply chain. On a pure carbon assessment their use should be much more prevalent, however the lower structural performance and slower construction techniques tends to limit height, impacting the urban density achievable.

Final thoughts

Ultimately, reducing carbon is essential, but it cannot be the sole driver of design decisions if it creates buildings which aren’t productive, enduring, regenerative, and don’t contribute positively to the city.

True long-term value comes from balancing carbon with adaptability, quality, usability, and durability. In dense urban settings, this means carefully weighing the reuse of existing structures against the benefits of new development and considering how buildings can evolve over time. Flexibility, disassembly and material choices all play a role in creating spaces that are not only low carbon. but also, resilient and future ready.

By broadening our focus beyond carbon alone, we can deliver buildings that perform environmentally, socially, and economically for decades to come. What we need is a unified framework- led by government, implemented by all planning departments. We think this should be linked to the Part Z regulations, but give weighting towards projects that can deliver urban density and productive cities; giving clarity to the balance between design drivers to enable us to do this consciously, considerately and responsibly.

The most sustainable building is an existing one; the least sustainable is an empty one.