The rise of a retrofit approach in urban landscapes

Earlier this year, Marks & Spencer won a court battle over the bid by DLUHC (now renamed Ministry of Housing, Communities and Local Government) to block the demolition of its existing London Marble Arch store. M&S can now demolish their property and build a new one.

Adopting a demolish to rebuild and replace strategy is a common approach on the basis that new buildings should be designed and perform better. That’s not new. But with large property in busy, built-up urban areas like London, things are changing, exemplified by the then SoS's apparent keenness to favour a retrofit first approach on the M&S store.

When you look at large, often heritage property in urban areas, the focus is on affordability; would the maintenance and operating costs of a retrofit match that of a new build? Would this approach even give it the same lifespan?

Yet as our understanding of embodied carbon develops, this starts to become a big part of the equation. Reusing a significant part of an existing building’s structure means retaining its embodied carbon, to a point where it becomes an essential part of the overall carbon emission saving strategy.

Change of thinking

The definition of what makes a building “sustainable” is also evolving.

The trend is moving towards recognising whole life carbon, which factors in carbon emissions created during the construction and in the materials, plus from energy used as well as replacement, maintenance and end-of-life emissions. This gives greater significance to a ‘retrofit first’ approach.

Embodied carbon is a substantial component of the total carbon emissions of a building – typically 50% for residential property, 47% for industrial and 35% for commercial offices (commercial space uses proportionately more carbon post construction – with lighting, heating, and so on). Also, LETI states that for a development built to current building regs, about one third of whole life carbon emissions are down to embodied carbon. For an ultra-low energy building, this can jump to around 70-75%.

With so much of building’s whole life carbon emissions in the construction process, no wonder some developers are now looking at a retain and re-use element for certain types of large urban buildings.

One is Stanhope, according to Building magazine’s story here, which recently tweaked plans for its 60 Gracechurch Street development with a focus on retaining a substantial part of the existing 10-storey building to minimise the carbon impact of redevelopment.

This approach is something being undertaken by Willmott Dixon working with FORE Partnership on TBC.London. This scheme to create highly sustainable workspace next to Tower Bridge involves using a substantial part of the existing building in transforming it from outdated office space into a net-zero carbon in operation building.

TBC.London’s approach to embodied carbon is particularly impressive. Retaining a sizable amount of the existing structure is saving 6,365 tonnes of CO₂ from being unnecessarily emitted into the atmosphere.

Also, a circular economy approach to raw materials has seen bricks and soft furnishings upcycled and reused. One innovative element is the reuse of 20 tonnes of 1930s steel beams from the former House of Fraser department store on Oxford Street, which will save an estimated 48 tonnes of CO2 compared to using new steelwork -the equivalent to driving a car around the planet 50 times.

It’s also the first UK construction project to reuse steel from a pre-1940s building and is part of a strategy that sees 20% of the required steel coming from a reclaimed source, with the remaining steel containing a minimum of 56% recycled content.

Green energy meeting future demand

As part of the UK Government’s Net Zero 2050 Plan, the energy grid will become sustainable in operation using renewable sources. That means carbon emissions from the green and renewable grid energy will substantially reduce, resulting in embodied carbon from construction becoming more dominant in its impact.

Also, although future energy from renewable sources mean it is low carbon, scarcity and cost of energy will remain an issue, which will need to be addressed by both new build and retrofit solution.

Efforts to overturn a demolish-first approach in court shows the moral mood has not caught up with planning legislation. That may change, with authorities changing their planning policy in favour of a more sympathetic approach to retro-fit first. An example is Greater London Authority which is formulating its approach to retrofit in its planning policy.

However, even here, currently developers are required to submit documents showing that considerations on sustainability have taken place – rather than hard and fast commitments to certain targets. This is because – as the document itself says – local and national governments are still in the benchmarking phase.

Not ‘one size fits all’

The growth of a ‘retro-fit first’ approach will create new opportunities for the built environment, with an emphasis on new skills for understanding how we measure embodied carbon.

However, for most accommodation when it reaches the end of its life, a new-build approach will remain the only viable way to replace it. It’s about striking the balance, and for our town and city centres, retro-fit is set to become a more embedded solution.