Project Pete
CO2 to build a house
I often find it tricky to get a sense of proportion around carbon emissions and the relative importance of different sources. How much difference does it really make to use 'bags for life', turn a thermostat down or unplug the phone charger? Lately, I've been hearing more and more about the environmental impact of new construction. I overheard someone on the radio saying it is better to re-use an old building than demolish and build a new, more efficient one in its place. This is apparently due to the enormous carbon emissions associated with building materials in particular cement, concrete and masonry. Could this really be true? It sounded far fetched.
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Firstly it's interesting to get a relative feel for typical carbon emissions associated with different activities. For instance, a typical family car (travelling 12,000 miles per year) will emit about 1.8 tons of CO2 which is similar to a heating system running on gas which will emit around 2 tons. If your heating system is electric, then in the UK you're looking at 1.6 tons as of today (2022). Given the increase in renewables on the grid, this figure is likely to drop below 1 ton/annum for electric in the next decade and less than 300kg for those homes that can have a heat pump. Incidentally this is about the same as a return flight between Birmingham and Athens (370kg of CO2). To get a relative sense of all these numbers, I've plotted them on Figure 1.
So how do these activities compare with the CO2 released when building a house?
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Well, it takes 50 tons of CO2 to build a typical home in the UK today. I've replotted the numbers to include this in Figure 2 which shows how stark this number is in comparison! Building a new home is equivalent to running an electric heating system for the next 50 years in the UK. So, if I'm 50 years old and decide to become an environmentalist, given the following options, should I A) become vegan and ride a bicycle, or B) stay in the 1950s end of terrace house on my street I live in rather than moving into a new eco-build? OK this is perhaps a rather silly choice but perhaps you could do both.​
Figure 3 shows the distribution of carbon emissions associated with the various elements of a new build home. The bricks and mortar account for the most significant fraction, some 30 tons or 60% of the total. There are, however, new materials which provide an alternative to bricks, Hempcrete is one example. A composite of fast growing hemp stalks and lime, the makers of Hempcrete claim that 165kg of CO2 is sequestered for every cubic meter. That amounts to around 2.6 tonnes per house. Switching from bricks to Hempcrete across all UK new build would save ~6.5 Mega tonnes of CO2, equivalent to 15% of our aviation emissions. Other alternatives include rendered straw bales and log cabins. Personally I think this sounds quite appealing!
Figure 1: Relative carbon impact of daily activities
Figure 2: Relative carbon impact of daily activities including one-off CO2 cost to build a home in the UK today
Figure 3: Breakdown of different sources of carbon within a new build home