Why is the built environment important to climate change? We all live and work in buildings, and they provide us with shelter and warmth, belonging and protection. However the built environment is responsible for a huge 39% of all global carbon emissions, far higher than any other individual sector. This 39% can be divided into two distinct impacts: operational carbon, which is from heating, lighting and cooling our existing buildings, which is responsible for 28% of our emissions; and embodied carbon, which is from the materials our new buildings are constructed from, and from their transport and construction processes, and also from the replacement of materials and components over the life of the building and impacts from the demolition and end of life processes – this is responsible for a further 11% of global emissions.
Operational impacts are now regulated in most countries. These have been reduced (although still not enough) through successive national building regulations – across Europe these are based on the EU Energy Performance of Buildings Directive originally drawn up in 2002. Zero operational carbon new buildings are now possible, particularly through a combination of electric power from renewables and Passivhaus design – highly insulated and airtight buildings which use mechanical heat recovery to recover the heat from people and equipment in the building and use that to warm incoming fresh air. Using renewable electricity is also a key part of reducing operational carbon. This can be either from onsite renewables such as roof-mounted photovoltaics, or from the grid; UK grid electricity, for example, has gone from over 0.5 kg CO2e per kWh in 2010 to around 0.25 kg CO2e per kWh in 2020, and is predicted to reduce further in the coming years as more renewables are brought on line.
Embodied impacts on the other hand are still NOT regulated, in the UK or most other countries, although there are growing moves within industry to calculate impacts even without regulation. In the UK and other countries with ageing building stock, embodied impacts across the country are a lower percentage of the whole because there is relatively less new construction; embodied carbon is around 9% of the UK’s emissions, but around 16% of China’s, where they are building another 4% of their building stock each year.
The two materials with the highest total impacts, partly because they are used in such quantities and partly because of the carbon intensity of their production, are steel and cement. Globally, cement is responsible for 7% of all carbon emissions – which means that almost 65% of all construction emissions are from cement. There is a strong move amongst some therefore to build with natural materials, such as cross-laminated timber. The transport of construction materials is also part of embodied impacts, but is often ignored. Where materials are local, this is fine, as carbon emissions from transport are minimal. However, the UK imports over a million tonnes of steel from China each year. It even imports a small percentage of bricks from Bangladesh. Adding the carbon emissions from transport means that, by the time used in UK buildings, these Bangladeshi bricks are each responsible for 1.1 kg CO2e – or 2.5 times the emissions of a UK manufactured brick.
So, there is clearly a trade off between operational and embodied carbon. Does this mean we should demolish existing energy inefficient buildings and rebuild new energy efficient buildings? Or should we retain our existing building stock and refurbish it?
Most of us would agree that our historic buildings should be retained, as they add character, a sense of history and of place, and we find them aesthetically pleasing. However, what about a nondescript 1980s housing estate? What the calculations of whole life (operational plus embodied) carbon impacts show is that we should almost always be retaining our existing built environment, and retrofitting it to bring it up to modern levels of energy efficiency. The embodied impacts of demolishing existing buildings and building new are over double those of even the highest level of retrofit.
As I mentioned, embodied impacts in the UK and Europe are lower than the global average, because we replace only around 1% of our buildings each year. Of the buildings that will be standing in 2050, at least 80% have already been built. The flip side is that that means we have an ageing building stock which is often uninsulated and energy inefficient. These buildings are using more operational energy and therefore have higher operational carbon emissions. So – we need to retrofit!
My title did also promise to talk about the impact of climate change on the built environment. We know that the climate is already changing. We know that we will have to deal with far higher temperatures, and with increased flooding, in the future. What can we do, in areas which already suffer from high temperatures, or are at risk from flooding, or are simply in an area with mostly impermeable and also heat absorbing surfaces such as our cities? In the UK our buildings are generally well adapted to coping with cold winters, but less capable of managing the increasingly hot summers. For our health and comfort, we therefore need to retrofit for future climates, but still by using as little operational energy as possible. Rather than moving down the path of portable air conditioners which both use more electricity and also add to the external urban heat island effect, passive cooling measures including external shutters or planting trees for shading both streets and buildings should become the norm as they already are in historically hotter countries. For flood resilience, simple measures such as raising ground floor sockets, and adding door guards and air brick covers can reduce flood risk to your property, and more permeable green landscaping, rather than hard impermeable surfaces, can reduce the possibility of flash flooding.
It is clear therefore that we absolutely need to retrofit our existing built environment, both to reduce energy use and to adapt to the inevitable future climates we are facing. But how do we achieve all of this?
Firstly, we must minimise new build, in order to minimise the embodied impacts (remember 11% of global carbon emissions are due to building a small percentage of new buildings each year). The impact of embodied carbon is around half a tonne of carbon per square metre – so 50 tonnes of carbon for a modest home of 100 m2, most of which is emitted before and during construction. The world can no longer afford this price tag.
Where new building is absolutely essential (not just for developer’s profits or the desires of the middle classes) it should be zero operational carbon – there are no sensible arguments which say anything different, and the fact that this isn’t yet happening is a failure of both policy and industry. We also need to minimise the amount of materials we use, and make sure they are as low carbon as possible, and also consider how best to recycle and reuse construction materials. This article hasn’t touched on the huge impact of construction on our waste, but just within Europe construction is directly responsible for 36% of waste, and through mining and quarrying an additional 25%.
Second – and perhaps this should really be first – we absolutely need to retrofit existing buildings, both to reduce operational energy and carbon, and to ensure that our built environment is fit for future climates and will still provide adequate comfort and shelter from the new climatic conditions.
Finally, buildings are just one part of the socio-technical system that makes up the built environment. Our own behaviour, and our interaction with our buildings, is critical. We can all personally make a difference, through simple actions such as turning our heating down, or buying energy from a green tariff; or if we own a building considering how we can best retrofit for energy reduction and future climates.
We can and must do better.
This text is based on my input to a panel on climate change, held for the Virtual Festival of the Arts, Science and Ideas celebrating the 150th Anniversary of Newnham College, Cambridge on 10th and 11th July 2021.