By Professor Brian Norton
European Academies Science Advisory Council
European Sustainable Energy Innovation Alliance
Member of the EEWRC Scientific Expert Panel
Households consume 27 % of end-use energy in the European Union, second only to the 32 % of energy used for transport. Transport energy use is being addressed largely by replacement of the old with the new; older internal combustion engine vehicles replaced by electric cars and private vehicle use replaced by modal shift to new or improved public transport options. However, a similar replacement strategy for domestic buildings would be economic madness, socially unacceptable and logistically impossible. The huge increases in the energy and carbon embodied in the extraction of materials and production of cement, steel and glass incurred would take significant time, if ever, to be offset by subsequent operational energy savings. Such a replacement strategy is also unnecessary as much can be done to improve the energy performance of existing buildings.
As new energy-efficient dwellings are only a small fraction of the total EU stock, the thermal characteristics of existing dwellings dominate overall building stock characteristics. The extent and duration of that dominance of existing houses depends on the construction rate, floor areas, specifications of new dwellings and, indeed, the rate of energy improvement of existing dwellings. With average replacement rates for existing housing stocks in the EU being less than 0.1 %, the majority of Europe’s existing dwellings will still be in place in 2050. In the United Kingdom for example it has been estimated that around 75 % of dwellings that will exist in 2050 have already been constructed. Accordingly, achieving less overall energy use requires energy refurbishment of existing dwellings. The long lifespans of buildings and their associated infrastructures mean there are significant risks of locking-in undesirable suboptimal or partial refurbishments that rendering future energy performance improvements more difficult or expensive.
In recent years there has been a surge in the development and use of energy consumption models that depict whole dwelling stocks. This has been driven by an awareness that the available evidence-base could not indicate what interventions would be likely be successful in building refurbishment policies to reduce domestic energy use.
Energy consumption models that depict dwelling stocks combine a stock model and an energy model. The stock model describes the stock size, composition and renovation status, whereas the energy model describes the average energy intensities of the various segments of the stock.
Energy consumption models have been limited by paucity of observed validation data, inputs and assumptions not being transparent and underappreciating that a building does not consume energy; its occupants do so. The latter is particularly important, as can be explained by two examples. In new, or newly refurbished, energy efficient buildings, as it is affordable, occupants may choose higher or lower internal temperatures in cold and hot climates respectively; the energy use is then not as low as would be expected. For older buildings, occupants, over time, make improvements to thermal insulation, windows and heating and cooling systems; energy consumption is then not as high as would be expected. This is due to the latter expectation being often based on an energy rating calculated for the insulation and heating system present when the house was initially constructed.
The diversity of building energy demands are often complex and context-specific. Before making energy efficiency interventions, it is vital to understand the factors driving energy use in existing dwellings stocks. Relevant research in buildings and energy is usually carried out on relatively small samples of buildings. Studies of trends and patterns in energy demand in buildings that include simple descriptions of population and stock segmentations have been limited, with little common, transparent or prescribed data reported. The lack of large-scale monitored building energy-use data means there is not a robust detailed evidence base for effective policy frameworks. There is thus an urgent need for rigorous and detailed inter-disciplinary research that can provide a reliable and strong foundation of evidence-based policies for optimal refurbishment interventions that reduce domestic energy demand and lower energy bills.
Further reading
Gillett, W.B., Kalogirou, S.A., Morthorst, P.E., Norton, B. and Ornetzeder, M., 2025. Perspectives on decarbonisation of existing buildings in Europe. Renewable Energy, p.122490.
Raushan, K., Mac Uidhir, T., Salvador, M.L., Norton, B. and Ahern, C., 2024. A data-driven standardised generalisable methodology to validate a large energy performance certification dataset: A case of the application in Ireland. Energy & Buildings, 323, p.114774.