Factsheet: Standards and Guidance
A summary of relevant building and energy regulations and associated guidance.
There are a number of standards and guidance within the UK relating to energy efficiency in existing buildings. These include:
- Statutory Guidance - Approved Document Part L of the Building Regulations.
- Technical Standards - the Retrofit Standards Framework (British Standards PAS 2030, PAS 2035 and PAS 2038).
- Certification schemes such as EnerPhit.
The standards and guidance within these documents will not always be appropriate or achievable in listed and historic buildings. For further advice on energy efficiency interventions to historic buildings, see: Building Regulations, Approved Documents and Historic Buildings.
Statutory Guidance
Conservation of fuel and power: Approved Document L
Part L of the UK Building Regulations sets standards for the conservation of fuel and power in new and existing buildings. Approved Document Part L provides guidance on how to comply with energy efficiency requirements for heating, cooling, ventilation, lighting, and hot water. Part L includes requirements for building fabric (walls, roofs, floors, windows), heating systems, insulation, and the installation of renewable energy technologies. Compliance with Part L helps reduce carbon emissions, lower energy bills, and support the UK’s climate targets.
Part L is divided into:
- Volume 1: Dwellings
- Volume 2: Buildings other than dwellings
The regulations are updated periodically to reflect advances in building technology and government policy. The updated Part L in June 2022 now requires more stringent carbon emission reductions, enhanced U-values, lower maximum flow temperatures, improved lighting efficiency, as well as introducing a new Standard Assessment Procedure (SAP10) and Primary Energy metric.
Owners of existing buildings need to comply with Part L of the Building Regulations when:
- Installing, renovating or replacing thermal elements.
- Extending an existing building
- Adding a conservatory or porch
- Replacing building services
- Changing the use or energy status of the building
- Making changes to controlled fittings or services*
- Making consequential improvements**
(*) Controlled fittings are windows, external doors, roof lights and roof windows. Controlled services are space heating and hot water systems, mechanical ventilation and cooling, and fixed artificial lighting.
(**) Consequential improvements are required when an existing building over 1,000m² is extended, its capacity for heating or cooling per m² is increased, or fixed building services are installed. Consequential improvements may include improving the insulation of thermal elements, upgrading old services systems, or adding zero carbon energy-generating equipment. However, consequential improvements are not required to be carried out where it is not technically, functionally and economically feasible. There are also exemptions for listed buildings, scheduled monuments and buildings in conservation areas where energy efficiency requirements would unacceptably alter the building’s character or appearance.
Under Volume 1, paragraph 0.8; and Volume 2, paragraph 0.12:
'Work to a dwelling in paragraph 0.8 must comply with the energy efficiency requirements, where this would not unacceptably alter the dwelling's character or appearance. The work should comply with standards in this approved document to the extent that is reasonably practicable.' (Volume 1, page 3, paragraph 0.9)
'Work to a building in paragraph 0.12 must comply with the energy efficiency requirements, where this would not unacceptably alter the dwelling's character or appearance. The work should comply with standards in this approved document to the extent that is reasonably practicable.' (Volume 2, page 4, paragraph 0.13)
'The energy efficiency of historic and traditional dwellings should be improved only if doing so will not cause long-term deterioration of the building's fabric or fittings. In particular, this applies to historic and traditional buildings with a vapour permeable construction that both absorbs moisture and readily allows moisture to evaporate. Examples include those built with wattle and daub, cob or stone and constructions using lime render or mortar.
'New extensions to historic and traditional dwellings should comply fully with the energy efficiency standards in this approved document unless there is a need to match the external appearance or character of the extension to that of the host building. The work should comply with standards in this approved document to the extent that it is reasonably practicable.
'In determining whether full energy efficiency improvements should be made, the building control body should consider the advice of the local authority's conservation officer.' (Volume 1, paragraph 0.10 to 0.12, Volume 2, paragraph 0.14 to 0.16)
Appendix C paragraph C2: 'If it is not reasonable to meet the target U-values in Table C1, considering technical risk and practicality of the work in relation to the dwelling and impacts on adjoining buildings, then the U-value should be as close to the target value as practically possible.'
Approved Document L states that where the renovation of a thermal element is greater than 50% 'the renovation must be carried out so as to ensure that the whole of the element complies with paragraph L1(a)(i) of Schedule 1.' With the caveat, 'in so far as that is technically, functionally and economically feasible.'
Upgrading windows and fully glazed external doors is mentioned in paragraph 4.10 that where they 'cannot meet the requirements of Table 4.2 because of the need to maintain the character of the building' then 'single glazing should be supplemented with low-emissivity secondary glazing'. In addition, as per paragraph 4.23 'they should be well fitted and reasonably draught-proofed'.
Technical Standards
PAS 2035:2019
PAS 2035 builds on PAS 2030 by providing a comprehensive framework for whole-house retrofit projects for domestic buildings. It covers the entire retrofit process, including assessment, risk evaluation, design, installation, and post-installation monitoring. PAS 2035 defines roles and responsibilities for everyone involved—such as retrofit coordinators, assessors, designers, and installers—and emphasizes quality assurance and risk management to ensure long-term performance and occupant comfort.
Compliance with the PAS 2035 Standard is a requirement of all retrofit programmes deploying government funding.
PAS 2038:2021
PAS 2038 is a British standard specifically designed for the retrofit of non-domestic buildings (like commercial, public sector, and multi-residential buildings). It provides a structured approach for managing retrofit projects—from energy assessment and planning through installation, testing, and evaluation. PAS 2038 aims to improve energy efficiency and building performance in larger, more complex buildings, supporting the UK’s environmental and net-zero goals.
Certification Schemes
There are several retrofit certification schemes and target frameworks (such as Enerphit, AECB Carbonlite, LETI) that set strict performance targets based on different levels of retrofit or building architype. While these frameworks offer valuable benchmarks, Historic England advises that such targets are often not reasonably and practicably achievable for historic and traditional buildings, where they would risk unacceptably altering the buildings character or appearance and/or causing long-term deterioration of the building's fabric or fittings.
This is especially relevant for moisture permeable construction, which is designed to absorb moisture and readily allow moisture to evaporate. Applying inappropriate retrofit measures to such buildings can increase the risk of unintended consequences, including trapped moisture, fabric deterioration and health impacts to the occupants.
In these cases, Historic England recommends a ‘whole building approach’ that prioritises the long-term health of the building and its occupants, rather than aiming for standardised performance levels. This approach seeks to achieve an energy efficiency that is proportionate, sensitive to heritage significance and demonstrably ‘best for building’.
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