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by Sean Ronnie Hill on Aug 31, 2023
The UK introduced the Climate Change Act in 2008, committing to a 100% reduction in greenhouse gas emissions from 1990 levels by 2050. By 2019 the government was declaring a climate emergency. The gap between those two moments tells you something about the difference between setting targets and actually changing how things get built.
We've been working on low-energy, low-embodied-carbon design at RISE since we started in 2011. Here's how we think about the problem and what we've learned along the way.
The Construction Sector's Actual Impact
Buildings account for 45% of the UK's carbon emissions across their construction, operation, and maintenance. That figure encompasses everything from the energy used to manufacture a steel beam to the gas burned to heat a house in January to the lorry that takes demolition waste to landfill.
32% of landfill waste in the UK comes from construction and demolition. 13% of materials procured for construction are never used. These aren't marginal inefficiencies. They're structural problems that compound across every project, every year, across the entire industry.
The response to this can't be incremental. Slightly better insulation on buildings that still rely on gas boilers, slightly reduced waste on sites that still over-order materials, slightly lower operational energy in buildings whose embodied carbon hasn't been considered: none of this adds up to the change the sector needs to make.
Operational vs Embodied Carbon
The sustainability conversation in construction has historically focused on operational energy: the energy used to heat, cool, and power a building once it's occupied. This matters enormously, but it's only part of the picture.
Embodied carbon, the carbon locked into the materials used to construct a building and released during their extraction, manufacture, transport, and eventual disposal, is increasingly significant. For a well-insulated, low-energy building, embodied carbon can represent a large proportion of the building's total lifetime carbon impact. In some cases it exceeds the operational emissions over the same period.
This has direct implications for how we specify. Concrete and steel are the most widely used structural materials in construction and among the most carbon-intensive to produce. Concrete's cement component alone accounts for around 8% of global CO2 emissions. These materials have genuine advantages in terms of performance and durability, but their carbon cost needs to be part of the design conversation from the outset, not ignored in favour of compliance with operational energy targets alone.
At RISE we use lifecycle assessment thinking across our projects: understanding where the carbon is in a building, not just how much energy it will use once it's occupied.
The Case for Timber
Timber is the most credible large-scale alternative to concrete and steel for many structural applications, and engineered timber products, particularly cross-laminated timber, have extended its range considerably.
CLT is manufactured by stacking layers of lumber in alternating directions and bonding them under pressure. The resulting panels are dimensionally stable, structurally predictable, and strong enough for multi-storey construction. They're also considerably lighter than concrete, which reduces foundation loads and can simplify construction on constrained urban sites.
The environmental case is straightforward. Trees sequester carbon as they grow. When timber is manufactured into CLT panels, that carbon remains locked in the material for the life of the building. Responsibly managed forestry can provide a renewable supply without net deforestation. The manufacturing process is considerably less carbon-intensive than concrete or steel production.
CLT also performs well in fire, which is the most common objection. Dense timber chars rather than combusting: the char layer insulates the material beneath it, slowing the rate of burning considerably. The behaviour is predictable and can be designed for. Dalston Works in east London, a ten-storey residential building in CLT by Waugh Thistleton Architects, demonstrated at scale that engineered timber construction can meet rigorous fire safety requirements. The lessons of Grenfell relate to external cladding systems and fire spread, not to mass timber structural elements.
We have used CLT on the Sutton Churches Tennis Club pavilion and continue to specify it where the structural and planning context supports it.
Greenwashing and What Genuine Sustainability Looks Like
The construction industry's sustainability conversation is compromised by a significant volume of greenwashing: products and practices marketed as environmentally responsible that don't stand up to scrutiny when examined across their full lifecycle.
The test is lifecycle assessment: an evaluation of a material or product's environmental impact from raw material extraction through manufacture, transport, use, and eventual disposal or recycling. A material that performs well on one dimension, low operational energy, for example, while performing poorly on another, high embodied carbon or poor end-of-life recyclability, is not genuinely sustainable regardless of how it's marketed.
The questions worth asking about any material or system are: where did it come from, how was it made, what happens to it at end of life, and what's the total carbon cost across all of those stages? These questions are more demanding than asking whether a product has a green label, but they're the only ones that produce honest answers.
Materials Worth Knowing About
Beyond CLT, a number of materials are becoming more commercially viable as alternatives to conventional high-carbon options.
Hempcrete, made from the woody core of the hemp plant mixed with a lime binder, provides good insulation, is carbon-negative over its lifecycle, and is breathable in a way that suits the retrofit of older buildings. We've specified lime-based plasters and renders on several projects for similar reasons: they're low in embodied carbon, breathable, and repair well over time without the moisture problems associated with cement-based alternatives.
Mycelium composites, grown from fungal material, are beginning to appear in insulation and packaging applications. BioMason's biologically grown bricks eliminate the high-temperature kiln process that makes conventional brick-making carbon-intensive. StoneCycling produces bricks from construction waste, diverting material from landfill and reducing the demand for virgin aggregate. Washington State University has developed plant-based insulation as an alternative to synthetic products.
None of these has yet reached the scale or commercial availability of mainstream materials. But the direction of travel is clear, and the pace is accelerating.
What Legislation Can and Can't Do
The Building Regulations set minimum standards. Part L governs energy performance, and its requirements have tightened over successive revisions. The Future Homes Standard, introducing significant changes to new build energy performance, is working its way through the regulatory process.
Legislation is necessary but not sufficient. The regulatory minimum tends to become the industry standard, which means that buildings designed to comply rather than to perform well continue to underdeliver. The gap between what building regulations require and what Passivhaus methodology achieves is considerable. The gap between what a compliant building actually delivers in use and what it was modelled to deliver at design stage is also consistently wider than it should be.
The more reliable driver of change is client demand, informed by evidence. When clients understand the difference between a building that complies and a building that performs, and when the financial case for performance, lower running costs, better EPC ratings, higher asset value, is clear, the commercial incentive aligns with the environmental one.
That education is part of what we try to do with every client we work with.
What the Industry Needs to Do
The transformation of the construction sector's environmental performance requires change at every level: how buildings are designed, what they're built from, how they're constructed, how performance is verified, and how the industry learns from what it builds.
On the design side, the shift that matters most is from compliance thinking to performance thinking: designing buildings that will actually perform well in use rather than modelling them to meet targets and hoping the gap doesn't show up. This means integrating energy strategy from the first sketch, treating fabric performance as a design decision rather than a specification detail, and verifying outcomes through testing rather than assuming the model was right.
On materials, the shift is from defaulting to familiar high-carbon options to asking seriously what the lifecycle carbon cost of every significant material decision is, and whether a lower-carbon alternative exists that meets the performance requirements.
On construction, it means investing in the skills and systems required to build airtight, which is not how most of the UK construction industry currently operates, and treating airtightness as a contractual requirement rather than a design aspiration.
On verification, it means testing what was built rather than certifying what was designed, and taking the results seriously enough to change practices when the numbers don't match the targets.
None of this is simple or cheap in the short term. All of it is necessary.
Where We Stand
At RISE we hold Passivhaus Designer accreditation and have been applying low-energy, low-embodied-carbon design methodology across our residential and community work since we started. Sustainability has been part of our design methodology from the beginning, not something added in response to market demand or regulatory pressure.
The projects we're most proud of are the ones that demonstrate that high environmental performance and high design quality are not in tension. Douglas House, Herbert Paradise, the Ice Cream House, the Lexi Cinema: each of these shows what it looks like when technical ambition and design ambition point in the same direction.
That's the standard we're working towards on every project. If you're planning a project and want to understand what a genuinely sustainable approach could mean for your building, we'd be glad to talk it through.
→ Email us at architects@risedesignstudio.co.uk
→ Or call the studio on 020 3947 5886
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