Does the UK’s low-carbon energy future make the push for zero carbon buildings a step too far? Are we in danger of emitting more carbon overall by making buildings more complex to reduce future energy use?
A few years ago (2007 to be exact), I took part in a piece of research into the embodied carbon of buildings constructed to the then-current building regulations. The surprising upshot was that the embodied carbon was equal to about 25 years of operational carbon emissions from the “ambient” building – heated / cooled to working temperatures, and lit appropriate to the internal activities, i.e. maintaining the internal conditions the structure was designed to achieve.
So, for a new building, half of the total carbon it will emit in the first 25 years will be given out during construction – in mining / extraction of its raw materials, conversion into usable products, transportation, and assembly into the finished building ready for use. And, by implication, the more complex we make these buildings to improve their energy efficiency, the more carbon we emit now to reduce future operational emissions.
In our gallop to reduce our energy consumption by 80% on the back of the climate change threat, we now have “zero carbon” targets for new homes by 2016, and commercial buildings by 2019, but in setting these worthy objectives, are we losing sight of the bigger picture? Is there a point of diminishing return where we are at risk of spending more carbon now to create efficient buildings than we will ever save in the future, and if so, where is it?
Let’s also factor in the carbon intensity of energy. At present a kWh of UK electricity has a carbon intensity of around 500 gCO2e/kWh, i.e. every kWh of electricity in the grid has given off 500g of CO2e into the atmosphere. But energy is also being “decarbonised”, with some forecasts having the carbon intensity of UK electricity as low as 100 gCO2e/kWh by 2030, and most getting down to 300 gCO2e/kWh or lower in the same period. In the next few years, as we move to low carbon energy, saving future energy will reduce overall carbon emissions far less than saving energy at present – fact.
So, on the face of it, “zero carbon” targets alone whilst good for the pocket in terms of energy bills may have a diminishing – and possibly negative – return on the carbon investment if increased complexity “costs” more higher-carbon energy now than it “returns” in lower-carbon energy in the future.
Is there a better way?
Performance targets need to take into account not only the carbon the buildings will emit over the next 25 years or so, but also the carbon given off to provide the buildings in the first place – set a “Carbon Allowance” for a buildings’ total carbon (say, per sq.m, by use – housing, retail, warehouse, school etc) over the first 25 years of its life. And then leave Clients and designers to decide how to spend it – on complex high-carbon buildings with low running costs, or on simpler buildings with low initial carbon, but higher running emissions.
Because in 25 years time, the carbon impact on the planet will be exactly the same.
Barry Phillips Smith, Director, bps eco ltd. Email: firstname.lastname@example.org Environmental Consultant, Construction & the Built Environment