The most sustainable building you ever build is the one you never build; the second most sustainable is the one that you refurbish; and the third most sustainable is the one where you use materials with the lowest embodied carbon. That’s why our development approach is to recycle first. And it’s why we’re focusing on materials.

As an industry, if we’re to meet our commitment to the Paris Agreement, we collectively have to accept that buildings can be a significant source of environmental impact and do everything we can to engineer carbon out of them.

When you operate a building, you can increasingly do that with renewable energy. So, over time the operation of a building will have comparatively less environmental impact and construction more. A lot of the buildings that go up today are around 1,000kg of embodied carbon per m². British Land is working to halve embodied carbon in our developments to below 500kg per m² by 2030.

So, how to halve embodied carbon? It always reminds me of my son singing “Recycle, recycle, recycle” from Peppa Pig. You can save up to 40% embodied carbon in a building by recycling what you already have, such as reusing existing core. Our development process therefore now requires our project teams to justify why they may want to take down a building, explaining why it can’t be refurbished.

Timber isn’t the only answer

We also look to use materials with the lowest embodied carbon. Cross laminated timber has a lot going for it – you can use it structurally, it’s clearly renewable and holds its carbon (as long as you don’t burn timber, you don’t release the carbon stored in it). So, its main carbon impacts are in its manufacture, transport and glue. But there are challenges around where you can use timber in a building and important areas of education around fire safety, acoustics and air handling.

In addition, if we all pursue timber as the path to get to net zero buildings, we’ll just displace the problem. We can’t be myopic in our approach. There are about 17 timber-led designs on the drawing blocks in London at the moment. That’s probably well over 100,000 trees that will be felled. So, there are questions about supply, about where and how those trees will be replaced.

With a bit more exploration, laminated bamboo has the potential to complement timber. It grows four times faster and, even with shipping, can have a lower carbon impact, plus it’s as strong as steel. With proper bamboo management, you can also protect bits of rainforest and get people out of poverty in marginalised communities. You can also use bamboo in shallower floor profiles, which can mean you get more floors in a building and expand the lettable area.

Other materials are catching up to net zero targets too. We recently designed a scheme two different ways – one using timber and the other using recycled steel and Cemfree, a cement-free alternative to conventional concrete that can save up to 80% of embodied carbon. The difference in embodied carbon between the two approaches was strikingly small. It surprised all of us.

Over time, new materials will come through as well. There’s a company called Biohm making composite boards out of orange peel and insulation from mushrooms (mycelium). Other companies are starting to use cardboard for duct work – those zinc or chrome covered tubes where all the air conditioning duct work goes across a building. There are people looking at our industry from the outside and creating products from things we’ve never thought about, potentially eliminating the embodied carbon of whole product categories and minimising that environmental impact.

We’re all learning our way through this

We all need to rethink what a ‘good’ building is. Looking at how people will want to occupy them in the future and what they’re going to ask for, it seems likely that this won’t be about density and that it will be about low impact buildings. We need to move away from the mindset of “well, it’s not a BCO standard building and we like big floor plates”, towards greater recognition of refurbishments as far more environmentally desirable than brand new buildings.

What’s needed is systems change. It can’t just be developers like British Land or one part of the design industry saying let’s change materials. The whole system has to change. This means the industry coming together around R&D to test and prove things like safety, strength, acoustics, air handling and energy performance. It means investors and insurers working with us to get comfortable with buildings constructed in different ways; contractors knowing how to work with new materials; agents being willing to get behind low carbon buildings and sell them; customers confident to occupy them.

The job of planners, regulators and various industry bodies is to protect people, and rightly so, but we all have the job of protecting the planet as well. They can play an important role, including making the many compliances for different codes and standards that have to be met when building something, clearer, more consistent and simpler.

We’re all learning our way through this. So, if you’re at the start of your embodied carbon journey, it’s great that you’re thinking about it. And I encourage you to be exploratory. The more that we can keep a research and development mindset and a willingness to share the better.

We’ve made a commitment at British Land to share learnings as we go. There’s no such thing as a stupid question at the moment. There’s only, how can we help the planet, has anyone done it and do we have the capacity to do it? Let’s approach this from a place of partnership.

British Land supports the Architects’ Journal’s RetroFirst campaign, which calls for action to slash embodied carbon emissions in construction by encouraging greater use of retrofit and refurbishment.