Our Approach to Sustainability in Modern Construction

The construction industry accounts for a significant share of global carbon emissions, both through the energy used in buildings over their operational lives and through the carbon embedded in the materials used to build them. It is also an industry that is slow to change its habits, partly because of genuine technical constraints and partly because the incentives for clients, contractors and designers do not always align in ways that reward long-term thinking.

At Cat Street Collective, we take the view that sustainability in construction is not an optional extra or a compliance exercise. It is a design discipline that, when applied from the beginning of a project, produces buildings that are better in every sense: more durable, more efficient, more adaptable and more honest about what they cost the world to make. Here is how we think about it.

Why sustainability has to start early

The most common mistake in approaching sustainability is to treat it as a late-stage filter rather than an early-stage input. A project where the design is largely settled before sustainability criteria are considered will find itself retrofitting solutions onto a form and a material palette that were not chosen with those criteria in mind. The result is compromise: more expensive, less effective and often less coherent than a project where sustainability was part of the conversation from the first sketch.

The decisions that have the greatest impact on a building's sustainability performance are made very early. Site orientation, building form, floor-to-ceiling heights, the ratio of glazing to solid wall, the structural system and the primary structural material: all of these are essentially fixed by the time a planning application is submitted. If the sustainability ambitions of a project have not shaped these decisions, the opportunity to make the most significant improvements has already passed.

This is why we insist on including sustainability criteria in the brief-writing process, before any design work begins. It is also why we engage specialist sustainability consultants during concept design rather than at the end of the technical design stage. The marginal cost of this approach is small. The difference in outcome is substantial.

What earlier civilisations understood about building

It is worth stepping back from contemporary sustainability frameworks to ask what builders have always known. The vernacular building traditions of every region developed, over centuries, in response to local climate, local materials and local conditions. A traditional timber-framed barn in the English Midlands, a rammed-earth dwelling in the Sahel, a stone croft on the Scottish islands: each of these was built with an intuitive understanding of how to use available materials efficiently and how to create shelter that works with rather than against its environment.

Platforms such as Eski Tarih, which documents historical practices and ways of life, are a reminder that many of the principles we are now trying to systematise in rating schemes and carbon accounting were once common sense embedded in craft tradition. Earlier builders could not afford to waste materials or to ignore climate, because they had no energy subsidy to compensate for a building that fought its environment rather than working with it. The results were often remarkably well-adapted structures.

This is not an argument for returning to pre-industrial methods. Modern buildings have demands, including fire safety, accessibility, acoustic performance and internal environment control, that vernacular traditions were not designed to meet. But it is an argument for learning from what works rather than assuming that contemporary solutions are always superior to older ones. Some of the most effective sustainability measures, thick walls, good orientation, natural ventilation, deep overhangs, passive solar gain, are not new discoveries. They are rediscoveries of what thoughtful builders have always done.

Embodied carbon: the often overlooked half

The sustainability conversation in construction has historically focused on operational carbon: the energy used to heat, cool, light and run a building over its life. This is a legitimate concern and one that building regulations have progressively tightened. But it has tended to crowd out an equally important consideration: embodied carbon, the carbon released in producing, transporting and assembling the materials a building is made from.

As operational energy performance has improved, driven by better insulation standards and more efficient systems, embodied carbon has become a proportionally larger part of a building's lifetime carbon footprint. In a very well-insulated building with good renewable energy provision, embodied carbon can account for the majority of total lifetime emissions. Ignoring it while focusing on operational performance is no longer a coherent approach.

Embodied carbon is harder to measure than operational carbon, because it depends on supply chain factors that are not always transparent and on assumptions about building lifespan and end-of-life scenarios that are necessarily speculative. But the tools for measuring it have improved significantly, and the willingness to engage with the numbers, rather than leaving them unexamined, is an important marker of serious sustainability intent.

Our approach is to calculate embodied carbon at concept stage, using the best available data, and to set reduction targets before the structural and material design decisions are fixed. Concrete and steel, the two structural materials used in most commercial and larger residential buildings, are significant sources of embodied carbon. Alternatives, including engineered timber, and hybrids that use concrete and steel more selectively, can reduce this substantially without compromising structural performance.

Material choices and supply chain transparency

Material selection is one of the most consequential decisions in a sustainable building programme. The choice of structural material, as noted, has a large effect on embodied carbon. But the choices made at a more granular level, the insulation, the cladding, the floor finishes, the joinery materials, also accumulate into a significant impact.

We ask our supply chain to be transparent about the origin and production of the materials they provide. This is not always easy. Construction supply chains are long and often poorly documented. But the information is increasingly available for those who ask for it, and the willingness to ask is itself a signal that changes supplier behaviour over time.

Timber is a particularly important case. Timber from well-managed forests, certified by credible schemes such as FSC or PEFC, is a genuinely low-carbon material that sequesters carbon as it grows. Timber from uncertified or poorly managed sources can have a negative land-use impact that offsets its other advantages. The difference between the two is not visible in the finished building; it requires engagement with the supply chain.

We also consider the end-of-life of materials at the point of specification. A material that is difficult to separate and recycle at the end of a building's life is a problem that is simply deferred. Designing for disassembly, where connections and junctions allow components to be separated and reused rather than demolished and landfilled, is an emerging practice that we incorporate into our design process where it is practically achievable.

Designing for longevity and adaptation

The most sustainable building is the one that does not need to be replaced. This sounds obvious but it has significant implications for how buildings are designed. A building that is built to last, with durable materials, robust detailing and a structure that can accommodate changing uses over time, will outperform a building that is cheaper to construct but needs significant intervention or replacement within a generation.

Longevity is partly about material quality and partly about adaptability. A building whose internal layout is locked into a specific use by its structural system is a building that becomes redundant or requires major intervention when that use changes. A building with a structural system that allows internal reconfiguration, or that can accommodate additional floors or extensions without compromising structural integrity, is one that can respond to changing demands without being demolished.

This is a long-term perspective that does not always align with the incentives of speculative development, where the primary concern is the cost and value at the point of sale rather than the performance over decades. But it is the perspective that genuinely sustainable construction requires, and it is the perspective from which we approach every project.

What our approach looks like in practice

In practice, our sustainability approach means that every project begins with a sustainability brief that sets out specific targets for operational energy performance, embodied carbon, water use, material sourcing and end-of-life strategy. These targets are proportionate to the scale and type of project, but they are always present and always considered from the earliest design decisions.

It means that we carry out post-occupancy evaluations on completed buildings to understand whether the performance predicted at design stage is being achieved in practice. The gap between predicted and actual performance in buildings is a well-documented problem. Closing it requires feedback loops that most construction projects do not have. We have built those loops into our process.

And it means that we talk honestly with clients about the real costs and benefits of sustainable construction. Some measures cost more upfront and save money over time. Some cost more throughout and deliver environmental rather than financial returns. Clients who understand what they are investing in, and why, make better decisions and are more committed to maintaining the sustainability performance of their buildings after practical completion. That commitment is what turns a well-designed building into a sustainably operating one.