Glossary of Terms

Carbon emissions

The most common greenhouse gas is carbon dioxide (CO₂), sometimes referred to as 'carbon'. The other GHGs also have a warming effect on the earth’s atmosphere, but their potency differs from CO₂. In order to calculate the total effect of the gases, each is converted into values that are equivalent to carbon dioxide (CO₂ₑ), which are then added together.

Carbon versus greenhouse gases

Global warming is caused by the emission of greenhouse gases (GHGs). The most common of these is carbon dioxide (CO2, typically abbreviated as simply ‘carbon’), but there are many other gases that contribute to global warming, three of which include methane (CH4), nitrous oxide (N2 O), and fluorinated gases (F-gases). Each GHG has a different warming effect on the earth’s atmosphere, F-gases for example are relatively small in volume but can have a global warming potential (GWP) up to 26,000 times greater than carbon dioxide. In order to sum the total effect of all gases, each is converted into its equivalent CO2 warming effect and all CO2 - equivalents (CO2 e) are then summed.

Source: US EPA (2015)

Climate change

The Earth's natural climate has historically been in a continued state of change, with naturally occurring greenhouse gases (GHGs) essential to our existence. However, human activities have directly increased these levels and, as a result, human produced GHGs are the leading cause of the earth’s now rapidly changing climate.

Comfort creep

In terms of buildings, comfort creep refers to how, over time, we become used to gradual changes in the temperature (and other areas).

Conservation Areas

Conservation Areas are designated places of special architectural and historic interest. In conservation areas there are additional planning controls and considerations in place to protect the historic and architectural elements which make these places special. These extra planning considerations are increasingly a source of debate, often claimed to act as a barrier to the necessary energy efficiency upgrades that the historic building stock needs to meet the UK’s net zero goals. Understanding the nature of properties in CAs can provide valuable insights to support evidenced and well-designed activities to improve the energy efficiency of homes.

Decarbonising the power sector

Decarbonising the power sector or ‘the grid’ means reducing the emissions per unit of generated electricity. The power sector has been a major success story, with carbon emissions falling by 67% between 2008 and 2019 – the biggest reduction of all sectors in the UK. This has been achieved by reducing our reliance on coal-fired power, increasing the use of renewables such as wind turbines and biomass utilisation.

Embodied carbon

This refers to the lifecycle emission of CO₂ₑ produced during the manufacture and transportation of materials, the construction process and the end-of-life aspects of a building.

Energy Performance Certificate (EPC)

An Energy Performance Certificate (EPC) is a certificate intended to indicate how energy-efficient a property is. EPC has been required in Europe for the rent, sale, or construction of buildings since 2013. However, they have been in use in the UK since 2007, with 23 million EPC records generated in the UK, since its introduction (Few et al, 2023). In the UK, EPC rate the energy efficiency of a property on a scale A-G, with A being the most energy-efficient and G being the least (Few et al, 2023).

The English Housing Survey demonstrates that the proportion of all dwellings in the highest SAP energy efficiency rating (EER) bands A to C increased considerably between 2008 and 2021, from 10% to 47.5% (EHS, 2023). In this same period, the number of pre-1919 dwellings with a band A to C rating increased from 1.1% to 18.7%. This is in fact a very significant change for traditional buildings over time: a growth of 16.3% (2008 to 2021) pre-1919s rated B and A-C, compared to a growth of only 3.6% for the total stock of sampled dwellings.

The Standard Assessment Procedure (SAP) is the methodology used to assess and compare the energy and environmental performance of dwellings; it is the model underlying the EPC in the UK. Its purpose is to provide accurate and reliable assessments of dwellings that are needed to underpin energy and environmental policy initiatives (DESNZ, 2023). SAP uses factors relating to the physical building (for example, building form, insulation, solar gains, heating system efficiency) and assumptions regarding the occupancy and heating schedule to calculate the regulated energy use of the building (Few et al, 2023).

It is broadly recognised that there are issues with the current EPC approach: for example, only 3% of the 229 respondents to Department for Business, Energy & Industrial Strategy and Ministry of Housing, Communities & Local Government's Call for Evidence (July 2018) thought EPCs were reliable, and only 6% thought they were effective at encouraging action. Work is required to improve EPC calculations, recommendations and costings for traditionally constructed buildings (Historic England, 2022). The current model and its underlying assumptions are particularly poor for traditional construction and materials. For example, they use assumptions about materials made after 1965 by default and apply these to traditional construction (Historic England, 2022). Based on their calculated operational energy usage, pre-1919 averaged 23 fewer points in the Standard Assessment Procedure (SAP), compared with post-1990 properties (DCLG, 2015). The current EPC ratings (based on SAP methodology) are not effective at accurately measuring building performance, particularly for traditionally constructed buildings, they perceive traditional buildings to perform poorly, even though case study evidence demonstrates this is largely not the case (Historic England, 2022).

Environmental Product Declarations (EPD)

An EPD is a document which transparently communicates the environmental performance or impact of any product or material over its lifetime. Within the construction industry, EPDs support carbon emission reduction by making it possible to compare the impacts of different materials and products in order to select the most sustainable option. An EPD is usually valid for five years, and is generated according to the relevant standards. Construction EPDs are based on the ISO 14040/14044, ISO 14025,EN 15804 or ISO 21930 standards.

Energy Use Intensity (EUI)

EUI is the total energy consumed by a building divided by its total floor area. It is used to make meaningful comparisons between building energy performance that avoid misleading results that occur to difference in size.

Maintenance versus repair

Maintenance can be defined as “routine work necessary to keep the fabric of a place in good order”

Repair can be defined as “work beyond the scope of maintenance, to remedy defects caused by decay, damage or use, including minor adaptation to achieve a sustainable outcome, but not involving alteration or restoration”.

Net carbon

Balancing carbon dioxide emissions against capturing or eliminating existing atmospheric carbon dioxide is key to achieving carbon neutrality. It requires a rapid reduction in carbon emissions and, where zero carbon emissions cannot be achieved, the remaining carbon should be offset.

Operational carbon

These are carbon emissions produced during the operational or in-use phase of a building, such as through heating and lighting.

Renewable and low carbon energy sources

Different energy sources produce different amounts of GHG emissions. During the last decade, renewable and low carbon energy sources such as wind, solar and biomass have successfully replaced traditional fossil fuels like coal, gas and oil.

Retrofit

Retrofit is the process of improving the energy and environmental performance of buildings through technical interventions. Good retrofit considers the unique properties of a building including the building characteristics, building services but also very importantly, the people.

Sequestered carbon

Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide and will likely play a key role in helping meet net zero targets. Natural forms of carbon storage include forests, which store carbon in their timber and within the soil.

Temperature adjusted emissions

Greenhouse gas emission from energy consumption and emissions in the buildings sector are strongly influenced by weather conditions – particularly temperatures during the winter. To allow meaningful evaluation of trends in emissions, the figures need to be temperature-adjusted. Temperature-adjusted emission figures are undertaken by analysing the relationship between emissions data and quarterly Heating Degree Days (HDD).

Thermal performance

In terms of a building, this refers to the efficiency in which it retains, or prevents the passage of heat. Materials with a good thermal performance do not readily transmit heat.

References

1. Department for Energy Security and Net Zero (DESNZ) (2023). 'Energy Company Obligation SAP and RdSAP Amendments'. (Accessed: November 2023)
2. Department for Business, Energy & Industrial Strategy and Ministry of Housing, Communities & Local Government (2018). 'Call for Evidence. Energy Performance Certificates for Buildings'. (Accessed: November 2023)
3. Historic England (2022). 'Energy Efficiency and Historic Buildings Energy Performance Certificates (EPCs) Case Studies'.
4. Department of Communities and Local Government (DCLG) (2015). 'English housing survey headline report 2013-14'. (Accessed: 1 March 2022)
5. English Housing Survey (EHS) (2023). 'English Housing Survey 2021 to 2022'. (Accessed: September 2024)
6. Few, J, Manouseli, D., McKenna, E., Pullinger, M., Zapata-Webborn, D., Elam, S. and Shipworth, D. (2023). 'The over-prediction of energy use by EPCs in Great Britain: A comparison of EPC-modelled and metered primary energy use intensity'. (Accessed: April 2023)