Net Zero Carbon Supplementary Planning Document

8. Policy NZC4 – Existing Buildings

8.1 Policy NZC4 requires that for developments relating to existing buildings (including extensions and conversions) applicants should demonstrate that sustainable construction and design has been considered in line with Local Plan Policy CC1. Policy NZC4 requires that applicants consider the alternatives to fossil fuel boilers and submit an assessment of low carbon energy supply options with their application.

8.2 Applicants are also encouraged to demonstrate how sustainable design, material choices and construction methods will also reduce carbon emissions through construction and operation. The Council recognises the significant opportunity to reduce the District’s carbon burden by retrofitting existing building stock, and will apply significant weight to proposals that deliver energy and carbon savings in existing buildings. The guidance in this section aims to outline a range of potential carbon-saving interventions in existing buildings according to the energy hierarchy.

8.3 Policy NZC4 encourages an approach to existing buildings that pursues energy efficiency measures, low carbon energy supply, and renewable energy generation, relevant to the scope and scale of the proposed development/ redevelopment.

8.4 Retrofit strategies can be identified by the level of intervention, including:

• very low cost or free quick wins;
• low cost and technically easy measures;
• high cost and technically difficult measures and deep retrofit requiring technical expertise.

Fabric First Approach

8.5 These measures are often at a lower cost and quick to implement, but form an important part to lowering carbon emissions from existing buildings. Measures can often be made in operation or continued use of the building and can include:

• Energy saving measures: fixing draughts or areas of damp, installing low energy lighting or appliances, and reducing wasted energy through behavioural change.
• Water saving measures: fixing leaks and reducing total demand for water through fittings and or behaviour change.

8.6 Building fabric interventions; upgrading windows and doors, installation of secondary glazing, improved levels of insulation (cavity wall/ceiling insulation/raft roof/loft/ floor), and chimney improvements.

8.7 Building fabric upgrades and improved energy efficiency should always be addressed prior to low carbon energy sources or renewable energy.

Employing low or zero carbon technologies

8.8 NZC4 requires all developments to consider alternatives to fossil fuel boilers through the submission of a planning application. NZC4 requires that applicants assess, and implement where feasible, low or zero carbon technologies as an alternative to new fossil fuel boilers. This assessment should be presented in a Design Statement proportionate to the type of application e.g. where a small extension is proposed it may not be feasible to replace a fossil fuel boiler but fabric first measures should still be considered.

8.9 Applicants should consider the use of the following for retrofitting into existing buildings and should refer to the guidance provided on the technologies in Section 5 above:

• Air source heat pumps
• Ground or water source heat pumps
• Domestic hot water storage
• Heat recovery systems
• Direct electric heating
• Energy storage
• Biomass heating
• Combined heat and power
• Solar photovoltaic panels
• Solar thermal
• Wind generation
• Hydro

8.10 The UK Government's Heat andBuildings Strategy (2021)set out to define the transition to low carbon buildings, including halting any new gas connections to homes from 2025 (and replacement gas boilers from 2035), in favour of low carbon heat strategies. Alternatives to gas boilers are explored in Section 5, in this SPD. The Council will expect applicants to outline what alternative measures are feasible to be included within the development with reference to the site's context and any constraints.

8.11 Installation of heat pumps can provide economic benefits and will provide significant carbon emission benefits to homeowners. Installation of a heat pump could reduce a home's heating carbon emissions by at least 60% today (compared to a gas boiler system), and the home will decarbonise further over time as the electricity grid decarbonises. However, consideration should be given to any accompanying measures needed to make the existing building suitable for these. For example:

• Heat pumps can run more efficiently in well insulated buildings that are able to retain their heat for longer. Some existing buildings will need improvement of airtightness and/or insulation in order for the heat pump to provide good value for the occupant. Without this, running costs may become excessive due to the price of electricity.
• Because heat pumps typically deliver heat at a lower temperature, the building may need larger heat emitters (larger pipework and radiators or underfloor heating); the conventionally sized existing radiators used with an existing gas boiler are likely to no longer be suitable. Without the larger heat emitters, the system may not heat the building effectively to a comfortable temperature.

8.12 Mechanical ventilation with heat recovery is similarly most effective in buildings that have good insulation and airtightness.

8.13 Each building and low carbon heat and energy options should be appraised on a case-by-case basis. Homeowners should consult with a PAS 2035 accredited retrofit coordinator if possible, to develop a bespoke retrofit plan. Installation of a heat pump is a skilled activity; building owners should consult with a qualified and experienced MCS certified installer for a quote based on an in-person inspection of the building.

8.14 Energy efficiency approaches can also include improved air tightness, insulation, glazing, and ventilation strategy improvements in addition to consideration of overheating mitigation measures.

Recommended retrofit targets and quality assurance standards

8.15 Recommended targets that applicants could pursue in order to demonstrate that their proposal delivers significant benefits include:

• 40kWh/m²/year space heating energy demand: A target taken from the LETI Climate Emergency Retrofit Guide. Policy NZC4 expects this target to be considered and recommends that it is applied for proposals including alterations, extensions, and changes of use.
• LETI Climate Emergency Retrofit best practice guidance recommends: a space heat demand limit of <50 kWh/m2 /year; a hot water demand limit of 20 kWh/m2 /year; an energy use intensity (EUI) limit of 50 kWh/m2 /year; and for 40% of the roof area to be covered in PV panels
• The Passivhaus Trust retrofit EnerPHit methodology sets a space heat demand limit of <25kWh/m²/year, in addition to primary energy/primary energy renewable limit of <65.5kWh/m²/year, surface temperature limit of >17 degrees Celsius, summer overheating limit of 10% at >25 degrees Celsius, ventilation rate minimum of 30 m3/hour/person and airtightness limit of <1 air change per hour @ 50 Pascals. The Council considers that this would represent exemplary performance in an energy retrofit.

8.16 Significant weight will be attributed to applications that demonstrate considerable improvements to energy efficiency, carbon emissions, condition, and longevity of existing buildings – such as those which achieve the recommended targets above. A building that is low-carbon and affordable to run is more likely to remain in use in the long term.

8.17 The above targets from LETI and EnerPhit frameworks, where pursued, would need to be calculated using energy modelling methods proven to be accurate in their ability to predict buildings’ energy demands. Building Regulations National Calculation Methods SAP and SBEM are not well suited to this as they are not typically accurate in reflecting actual performance. Instead, the applicant is likely to find the most utility in alternative accurate energy modelling methods such as PHPP or CIBSE TM54. These can be used to plan and evaluate the performance of the retrofit, and to demonstrate the proposals’ benefits within the planning application.

8.18 Many of these targets may also be verified through actual in-use energy monitoring. Performance in line with the EnerPhit approach can be demonstrated via EnerPhit certification.

8.19 Finally, retrofit interventions have the opportunity to not only improve energy efficiency, potentially lower the cost of energy bills, but also to improve the thermal comfort of occupants and thus support the health and wellbeing of building users.

8.20 Certain standards are available to assure the quality of energy retrofitting, two of which are noted as follows. Application evidence of the implementation of these will be looked upon as a measure that is likely to improve the credibility and quality of proposals relating to existing buildings:

8.21 PAS 2035 is a best practice standardised process for retrofitting dwellings for energy efficiency in the UK. It allows retrofits to be Trustmark certified, providing security and reducing risks for building owners. Using PAS 2035, a risk appraisal can be carried out to demonstrate how retrofit measures have been carefully designed to minimise overheating risk (from increased airtightness) and minimise health risks to occupants (including condensation, mould and improper ventilation).

8.22 BS 40101 is the standard for building performance evaluation of occupied and operational buildings (using data gathered from tests, measurements, observation and user experience). This provides designers and procurers of buildings with insights into the performance of the building for the purpose of planning and implementing retrofit, modification and improved management of existing buildings.

8.23 Please also refer to the following external guidance:

• LETI Climate Emergency Retrofit Guide (LETI, 2021)
• Net Zero Carbon Toolkit (Etude, Elementa, Passivhaus, Levitt Bernstein, 2021); or
• Passivhaus Trust’s Retrofit Primer (version 2, 2022)

8.24 In an average home, fabric improvements or the installation of low or zero carbon technology are unlikely to require planning permission. However, planning permission may be required where the proposed measures affect the external appearance of a building. Applicants are urged to check what permitted development rights are available to them, and if unsure contact the Council before implementing these measures, or applying for planning permission.

8.25 Internal or external alterations to listed buildings will require listed building consent – please see the following section below.

8.26 Some measures noted in the above two sections require further consideration when dealing with historic buildings (designated and non-designated heritage assets, including locally listed buildings) and buildings in a Conservation Area. However, the sensitive retrofitting of energy efficiency measures and the appropriate use of micro-renewables will be encouraged, providing the special characteristics of the heritage assets are conserved in a manner appropriate for their significance. Applicants may find it useful to refer to guidance from Historic England²⁷ on Retrofit and Energy Efficiency in Historic Buildings (Historic England, 2020).

8.27 In line with new buildings, building fabric upgrades and improved energy efficiency should be addressed prior to low carbon energy sources or renewable energy. 

For further guidance please refer to the Council’s Energy Efficiency for Historic Buildings Guidance. This provides further details on the general principles and retrofit solutions for historic buildings.

²⁷ Historic England (2023), Retrofit and EnergyEfficiency in Historic Buildings.