Heritage and the Pathway to Net Zero

The stock of ‘heritage homes’

Generalised assumptions for 'heritage homes' [1] are used in the net zero and 6th carbon budget models:

• The supporting evidence for the 6th carbon budget estimates that there are around 540,000 ‘heritage homes’ in the UK, including listed buildings and homes in conservation areas (Element Energy, 2021). The CCC 6th carbon budget documentation estimates for heritage includes around 1.3 million ‘heritage homes’, including 400,000 listed buildings (CCC, 2020b)

However, both estimates are in fact underestimates of the historic stock:

• There are approximately 10,000 conservation areas (CAs) in England. A study by Noble et al (2017) mapping CA polygons with Output Areas matched to Census 2011 data estimated that there is a total of 2.8 million households in CAs
• Research by the Ordnance Survey in 2015 matching the National Heritage List for England to Postcode Address File (PAF) data found that there are an estimated 357,376 listed dwellings in England (Historic England, 2021)

Low carbon heating assumptions for ‘heritage homes’

• It is assumed that 50% of detached, semi-detached and terraced homes with a heritage classification are suitable for air-source heat pumps, and 75% are suitable for ground-source heat pumps. It is worth noting that the government-funded Electrification of Heat project has proven that there is no property type or architectural era that is unsuitable for a heat pump (Energy Systems Catapult, 2022). This suggests that amendments to the modelled assumptions for heritage are required for the seventh carbon budget
• Additional costs for installing low-carbon heat in ‘heritage homes’, above and beyond the cost of heat emitters, range from 25 to 75% uplifts per measure

The additional costs are expected to arise due to:

• Additional protection to conserve the fabric of the building during works
• The costs arising from the bespoke concealment of electrical and mechanical distribution systems
• Other costs associated with bespoke approaches required to preserve the character of the building
• Archaeological surveys

Fabric energy efficiency assumptions for heritage

The retrofit of energy efficiency measures to the fabric of heritage assets is currently subject to the same suitability constraints. The revised suitability criteria are expected to lead to a pessimistic increase in the portion of designated residential buildings suitable for retrofit (Element Energy, 2021).

It is estimated that 50% of the homes are suitable for internal and cavity wall insulation. However, none of them are suitable for external wall insulation. Along with this, 50% of the homes can benefit from secondary glazing windows or replacement with double glazing. Door proofing is doable for all homes, but replacing the door is not recommended. For loft insulation, all homes can be topped up to 300mm where partial insulation is present, and loft replacement is also an option for all dwellings. Lastly, underfloor insulation is suitable for 50% of the homes (Element Energy, 2021).

As a result of the above assumptions, a 183% average cost uplift is assumed for heritage homes for the 6th carbon budget (Element Energy, 2021). The uplift factors are influenced by the measures included in the energy efficiency packages which differ between the Net Zero pathway (to 2050) and the 6th Carbon Budget (2033 to 2037). Net Zero pathways (to 2050) assumed a 57% overall price uplift for heritage (Element Energy, 2021).

• Previous research by Parity Projects, considering retrofit of pre-1919 homes found that it would require about £2,500 or 9% more investment per home to bring them up to a similar standard (Parity Projects, 2021). This does not include professional fees so is not directly comparable with the CCC projections but is significantly different suggesting further research in this area is very much needed
• Similarly, the Element Energy research found limited evidence in the public domain on the cost uplifts which can be associated with retrofitting ‘heritage’ homes (Element Energy, 2021)

Footnotes

1. Homes with a heritage status are termed ‘heritage homes’ in the 6th Carbon Budget model evidence base. These include listed buildings and those in conservation areas.

References

1. Climate Change Committee (2020b). ‘The Sixth Carbon Budget Buildings.’ Available at: https://www.theccc.org.uk/wp-content/uploads/2020/12/Sector-summary-Buildings.pdf (Accessed: 10.09.23)
2. Element Energy (2021). ‘Development of trajectories for residential heat decarbonisation to inform the Sixth Carbon Budget (Element Energy) - Climate Change Committee.’ Available at: https://www.theccc.org.uk/publication/development-of-trajectories-for-residential-heat-decarbonisation-to-inform-the-sixth-carbon-budget-element-energy/ (Accessed 8.11.23)
3. Energy Systems Catapult (2022). ‘All housing types are suitable for heat pumps, finds Electrification of Heat project.’ Available at: https://es.catapult.org.uk/news/electrification-of-heat-trial-finds-heat-pumps-suitable-for-all-housing-types/ (Accessed 8.11.23)
4. Historic England (2021). ‘Indicator Data – Insights into the historic environment sector.’ Historic England. Discovery Identification and Understanding 2021.xls. Available at: https://historicengland.org.uk/research/heritage-counts/indicator-data/ (Accessed 8.11.23)
5. Noble,S., Plunkett, E., Sargoni, O.,  McLennan, D. and  Noble,M. (2017). ‘Socio-economic trends and growth in conservation areas. Final report.’ https://historicengland.org.uk/content/heritage-counts/pub/2017/socio-economic-trends-growth-conservation-areas-final-report-pdf/ (Accessed: 8.11.23)
6. Parity Projects (2021). ‘Energy-saving retrofit opportunities for pre-1919 homes.’ Available at: https://historicengland.org.uk/research/heritage-counts/2020-know-your-carbon/reducing-carbon-emissions-in-traditional-homes/ (Accessed: 9.11.23)