Why retrofit technology is important to the UK
The UK government is committed, via the Climate Change Act and the Carbon Budgets, to a 34% greenhouse gas emissions reduction target by 2020, and 80% by 2050, based on 1990 levels (as well as a 4th Carbon Budget target, soon-to-be-announced by Chris Huhne [update: announced 17/05/2011 as 50% reduction target by 2025]). How should we set about achieving these targets? Where should we focus our energy and attention?
This blogpost will obviously not attempt to answer these questions fully, rather, it will take an example – heating in the domestic sector – in order to explain why more effort should be undertaken on reducing the energy consumption of existing buildings than that of new ones. We will therefore first look at some energy consumption statistics, then compare a few studies, in the hope of convincing you that retrofit technologies are far more important than efficient new build, when it comes to meeting carbon emissions reduction targets.
While much popular attention is devoted to the reduction of emissions in electricity production – whether through wind turbines, solar panels, nuclear power stations or carbon capture and storage – this overlooks two very important aspects of the energy landscape: heat, and energy efficiency.
Energy efficiency represents the most viable means of reducing carbon emissions, because of the lower greenhouse gas abatement costs involved; studies by both the International Energy Agency and McKinsey, have shown this. Heat, meanwhile, is the single largest use of energy in developed (OECD) countries, claiming 37% of total energy consumption, as shown on the pie chart above.
Just over half of this heat is used in buildings: commercial & public buildings or residential dwellings, with the residential sector using nearly twice as much heat as the commercial & public sector. Clearly, most of this heat is used as low grade (less than 100°C) space or water heating.
The pie chart below shows the latest available final energy consumption data for the UK, per sector. The domestic sector, which represents just under a third of total UK energy consumption, uses 84% of its energy to provide heat, of which the vast majority is for space or hot water heating. It is this UK domestic sector, which predominantly uses energy for heat purposes, which we will use as an example to explain why the retrofit market is so important.
There are currently some 26 million dwellings in the UK, using an average of between 18,000 and 20,000kWh per year for heating, depending on the severity of the winter , , . Of these 26 million, the vast majority are expected to still be standing in 2050. A review of 5 different residential sector energy models  suggests that between 85% and 97% of the dwellings already built in 2006 will remain in 2050. What’s more, by considering the amount of new build that is expected to occur between 2006 and 2050, these studies predict that between 66% and 74% of the 2050 housing stock has already been built by 2006.
What this means in terms of the age of houses currently built is depicted in the graph below. This shows, for England, the proportion of houses that were constructed in a specific period (blue line), and a cumulative curve showing the total percentage of homes built during or before a specific period (red line). Using this curve as representative of the whole UK, we can see how 84% of UK dwellings were built before 1985, of which 24% were built in the 20 year period between 1965 and 1984, and the remaining 60% are at least a half-century old (give or take). Similarly, it shows how some 40% of UK dwellings were built before the end of the Second World War and that there has been limited recent construction; only 15% of dwellings were built in the last 25 years.
In short, this all serves to highlight an important cultural aspect in the UK housing market: despite significant construction in the first 40 post-war years, older properties seem to be valued above newer properties, explaining the combined phenomena of high proportion of retained pre-war properties in the housing stock and a lack of recent construction.
In energy terms, however, this is not positive; older properties are typically very poor in terms of energy efficiency, and therefore require more energy (especially for heating). For example, they are more likely to have uninsulated cavity or solid walls and single glazing (never mind draughts and leaking roofs!). This leads to the following obvious fact: these properties are shown to be too difficult and expensive to retrofit to new build standards. New build will be required to be “zero carbon” from 2016 onwards; this will ensure that emissions associated with the 1/3rd of 2050 dwellings that don’t already exist are minimised – certainly very important, though ‘all’ it achieves is to avoid emissions growth, as most existing buildings will remain!
One study  calculates that there is a global potential to cost-effectively reduce emissions in the residential and commercial sectors by approximately 29% of the projected baseline emissions by 2020. Moreover, for only a few percent of the total cost of residential buildings, thermal envelope (the part of the building shell responsible for insulation) improvements can reduce heating requirements by a factor of two to four . Nevertheless, two building energy models calculate that even in 2050, existing houses will have a combined space and water heating demand that is more than twice as large as that for new houses , with space heating energy use only reducing by 40% .
So, this all indicates that while retrofit insulation measures are important and feasible up to a certain point, it is uneconomical or technically challenging to bring existing dwellings’ thermal performance to a standard similar to that of new build.
Given that even these insulated existing dwellings will still have a greater heat demand than new build, the economic, energy and carbon performance of any potential future heating device is of relatively greater importance to the existing housing stock. And because there will be many more old, inefficient dwellings than new ones, even by 2050, the opposite is true as well: the existing housing stock should be of greater importance to future heating technologies. So, heating systems such as heat pumps, biomass boilers or combined heat and power systems have to be specifically designed for the technical challenge that retrofit properties pose. (The same applies to retrofit insulation methods, but this is already done to a far greater extent).
Hopefully, I have managed to convince you of the importance of retrofit to reducing emissions in the UK residential sector. Similar arguments apply, in a broader sense (i.e. including electrical demand, such as lighting), to the commercial sector, where one study suggests only 30% of currently existing buildings will be demolished by 2050. While retrofit is often considered cost-effective low-hanging fruit, its hassle factor is high (i.e. it is often only cost-effective once you know what your specific retrofit solution should be and, even then, the installation work can be difficult and very disruptive to the resident). There are few one-size-fits-all solutions in the retrofit space. Large-scale deployment will therefore require business models that can get around or deal with this issue, as well as residents who are open to the idea and understand that they stand to gain in both comfort and financial terms!
Let us hope that the Renewable Heat Incentive and the Green Deal will enable this.
 H. Singh, A. Muetze, and P.C. Eames. Factors influencing the uptake of heat pump technology by the UK domestic sector. Renewable Energy, April 2010.
 A.D. Hawkes and M.A. Leach. On policy instruments for support of micro combined heat and power. Energy Policy, August 2008.
 D.P. Jenkins, R. Tucker, and R. Rawlings. Modelling the carbon-saving performance of domestic ground-source heat pumps. Energy and Buildings, June 2009.
 Ramachandran Kannan and Neil Strachan. Modelling the UK residential energy sector under long-term decarbonisation scenarios: Comparison between energy systems and sectoral modelling approaches. Applied Energy, April 2009.
 Brenda Boardman and University of Oxford. 40% house. Environmental Change Institute University of Oxford, Oxford, 2005.
 Bert Metz and Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change. Climate change 2007: mitigation of climate change: contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge; New York, 2007.