9 Retrofit
9.1 Policy and Guidance Overview
• National
NPPF Chapter 2- Achieving sustainable development
NPPF Chapter 11- Making effective use of land
NPPF Chapter 12- Achieving well-designed places
NPPF Chapter 14- Meeting the challenge of climate change, flooding and coastal change
NPPF Chapter 16- Conserving and enhancing the historic environment
Historic England – Adapting Historic Buildings for Energy and Carbon Efficiency (2024)
Historic England – ‘Your Home’ online guidance
Sustainable Traditional Buildings Alliance (STBA) – Planning responsible retrofit of traditional buildings
LETI Climate Emergency Retrofit Guide
The Society for the Protection of Ancient Buildings (SPAB) Research into the Energy Efficiency of Old Buildings
• Regional
London Plan Policy SI 2 Minimising greenhouse gas emissions
London Plan Policy SI 4 Managing heat risk
London Plan Policy SI 7 Reducing waste and supporting the circular economy
London Plan Policy HC1 Heritage Conservation and Growth
• Local
City Plan Policy 38: Design principles
City Plan Policy 39: Westminster’s heritage
Westminster City Council – Planning householder retrofit how-to guides
9.2 Introduction and Guidance
Refurbishment and retrofit projects provide an important opportunity to improve the energy and water efficiency of existing buildings and reduce emissions, which is key to achieving net zero carbon by 2040 and addressing water stress in the capital. Retrofitting exiting buildings can also have a number of embodied carbon benefits, along with maintaining buildings of historical significance.
9.2.1 Retrofitting existing buildings
Whilst there are benefits with retaining existing buildings, it is recognised that many perform poorly in terms of heating and cooling and overall resource efficiency. By upgrading existing buildings to improve insultation, glazing and exposure to weather events, this can help to use less energy. Furthermore, by retrofitting buildings to use other sources of energy, thereby reducing the traditional reliance on gas systems, this can also mean that the energy used by buildings results in less carbon emissions overall.
Similarly, water use efficiencies help mitigate water stress, contribute to carbon and energy savings and help manage the need for new major infrastructure by reducing a building’s water demand. Water efficiency through retrofitting can also increase the energy efficiency of buildings by reducing hot water consumption and reduce costs on water bills.
The upgrade and reuse of existing buildings is a sustainable approach and can help to reduce higher upfront embodied carbon emissions associated with constructing new buildings. Retrofit can also enable existing and historic buildings, including listed buildings, to remain fit for purpose and in active use when sensitively adapted and upgraded. The responsible retrofitting27 of buildings which contribute to the special character of conservation areas as opposed to demolishing them also helps retain their distinctive character.
Many of the existing buildings in Westminster are constrained, for example by space or subject to a heritage designation, and so retrofitting may be more complex. A large proportion of the building stock in Westminster has a heritage designation, whether through statutory listing or being located in a Conservation Area, so finding sensitive and effective ways to improve resource efficiency of historic buildings is of vital importance.
Given the extent of heritage assets, Westminster is uniquely placed to lead in work on the area of responsible retrofitting of historic buildings and this work area will be a priority in order to tackle the issue of climate change. The council will also ensure the value of Westminster’s exceptional heritage remains and will continue to meet statutory duties to protect heritage assets. An approach to retrofitting measures that is iterative in nature and
27 In line with Historic England definition: Responsible retrofitting is an informed and integrated attitude to retrofit in a way that enables people to reduce the operational carbon of a building, improve energy efficiency, and/or improve a building’s resilience to the impacts of climate change. Responsible retrofit will take into account the building’s location, context, design, construction, materials and use, to ensure retrofit measures perform well and avoid adverse impacts to health, heritage and the natural environment.
looks for lower-cost and minimally invasive interventions can often be most effective and will therefore be encouraged first.
In all planning decision making relating to refurbishment & retrofit, the council will support and enable both the conservation of energy and the conservation of buildings, seeking innovative and sensitive solutions for responsible retrofit which deliver the highest possible standards of environmental & energy performance, giving significant weight to the public benefits of appropriate, demonstrable improvements in energy & environmental performance
The most effective retrofit solutions will optimise energy and water efficiency and ensure a safe, healthy and comfortable environment for occupants while protecting and enhancing heritage significance. The availability of trained and skilled trades people who can carry out the necessary works will be essential to delivering retrofit solutions. The council will seek opportunities to support skills development for a green economy as part of our Climate Emergency Action Plan
9.2.2 Approach to retrofitting existing buildings
The council supports responsible retrofit and expect proportionate measures to be taken to improve the energy and water efficiency all of existing buildings, including the most challenging building types: it is not a question of ‘if’ but a question of ‘how’.
In addition to the global climate drivers for retrofit the council recognises the local and more immediate challenges relating to building maintenance, year-round comfort, fuel affordability and environmental impact. Buildings can only be truly sustainable if they are comfortable, affordable, desirable and have minimal environmental impact.
Most buildings will be capable of some level of improvement and while for some buildings there may be a limit to the level of intervention that is possible, in many cases very significant improvements can be made.
The key to success is understanding – at all levels, from applicant to local authority to designer and contractor. In line with the Whole Building Approach set out in Historic England guidance28, this should be based on:
▪ An understanding of the building and how it performs;
▪ An understanding of the significance of the building;
▪ Prioritising interventions that are proportionate, effective & sustainable; and
▪ Avoiding & minimising harm & the risk of maladaptation.
By the same token, there needs to be a holistic approach to historic buildings. Achieving a truly sustainable built environment is complex and wide reaching, and – especially in the context of historic buildings – focusing on energy alone can lead to unintended consequences and a failure to achieve meaningful benefits. Issues such as health & wellbeing, safeguarding of occupants and building fabric, grid decarbonisation, embodied energy & the long-term
28 Adapting historic buildings for energy & carbon efficiency: HEAN 18 (Historic England, July 2024)
environmental impacts (positive & negative) of retrofit measures must all be considered if we are to achieve a truly sustainable built environment.
The council recognises the importance of buildings being ‘retrofit ready’, to safeguard buildings and occupants, minimise the risk of unintended consequences and maximise the likelihood of predicted benefits being realised. As such, we will champion a ‘maintenance first’ approach in all cases.
A holistic approach is also appropriate when assessing and interpreting ‘harm’ to designated heritage assets, and the council will recognise and give significant weight to the ‘public benefits’ of proposals in terms of climate change mitigation and adaption. As noted by Historic England29 , ‘Questions of scale and balance are important … The balance is likely to favour proposals which offer meaningful, long term environmental benefits (such as improving energy efficiency, thus reducing carbon emissions and helping to achieve Net Zero) whilst having a minimal impact on significance’.
Recognising the importance of safeguarding building fabric and occupant wellbeing in a changing climate, the council will also support appropriate adaptations to manage our changing weather patterns, in particular passive measures to combat overheating and ensure effective rainwater management.
While this guidance sets out many typical retrofit measures and provides general advice, the complex and sometimes unique nature of historic buildings means that generic guidance may have some limitations. Due to the unique nature of heritage assets, the balance of addressing climate change, protecting heritage assets and viability will need to be considered on a caseby-case basis. Applicants are encouraged to contact the council for pre-application advice
Applicants should take a coordinated or ‘whole building’ approach to planning and delivering all retrofitting projects as opposed to delivering piecemeal measures. Applicants are encouraged to develop a Retrofit Plan, which may form part of the Sustainable Design Statement, to help understand all of the individual pieces of work needed to improve the building, how these interact and any associated consequences.
The Retrofit Plan should include details of the building’s current performance and condition, including the identification of issues and locations where it is sub-optimal, options which have been assessed and how consideration has been given to this issue having regard to the impact upon the historic environment. Where the building affected is a listed building or within a conservation area, the impact of any retrofit measures on the building or area should be assessed and harm to their significance avoided
Where significance may be affected, applicants should demonstrate that proposals have been designed to avoid and then minimise any potential negative impacts. In this respect applicants should demonstrate adherence to Historic England guidance30, which advises the following steps to understand and mitigate potential impacts:
▪ Understand the impact of the proposal on significance
29 Ibid
30
▪ Avoid, minimise & mitigate harmful impact in a way that meets the objectives of the NPPF
▪ Look for opportunities to better reveal or enhance significance
▪ Justify any harmful impacts in terms of balancing the sustainable development objectives of conserving significance & the need for change
▪ Understand the public benefits
Applicants should also demonstrate how the building in question will be maintained before, during and after retrofit, and how the proposed works address future climate pressures including overheating and rainwater management.
A Retrofit Plan can help maximise the energy, health and comfort improvements delivered by retrofit and avoid unnecessary, costly or abortive work. Furthermore, in the context of historic buildings, a Retrofit Plan can help to identify measures to ensure that buildings are treated sensitively, having regard to the differences between modern and traditional construction practices.
A Retrofit Plan should include:
• Key building information including context, construction, current condition, historic significance and associated constraints, risks, and opportunities.
• Identification of factors present in the existing building that affect resource usage and/or adaptability to climate change effects.
• Main works proposed along with related strategies and details to mitigate any risks identified.
• The sequence of work.
• Resource efficiency strategy.
• A plan for monitoring and reporting resource consumption.
Not all retrofit measures require planning permission (see Table 10). Small scale changes can still often deliver dramatic outcomes. These could include thoughtful maintenance and repair; changing how the building is operated; repairing existing windows and doors and taking advantage of their special characteristics; installing secondary glazing and upgrading lighting.
The following considerations and questions may provide guidance when considering which of the sustainability upgrades set out in the following section will be most appropriate for a property:
• How is the building used? Can it be used more efficiently? Firstly, you should ensure that you are already undertaking measures that can be implemented at no cost, which involve changes to behaviour rather than the building fabric, and low-cost minor alterations and additions to make the building more resource efficient.
• What condition is the building in? You should first undertake any necessary repairs, ensuring buildings are in good order and are watertight. A damp building will be less thermally efficient, and this should be addressed before additional measures are considered.
• Consider the type of heritage protection that applies. Is your property a listed building or within a conservation area?
• What scope do you have to make changes? Freeholders will have the most scope, while leaseholders and tenants will be constrained by the terms of their lease and will require permission/consent of the freeholder/landlord.
• What is the budget? Each building is unique and costs will vary depending on the requirements. Consider the cost effectiveness, and the likely payback period of measures that will have a medium to high cost.
• What permissions/consents do you need to obtain? Some measures will be ‘Permitted Development’ for which planning permission is not required, as long as the property is not subject to an Article 4 direction or planning condition amending the Permitted Development Rights. For listed buildings it is likely that listed building consent will be required. Please refer to permissions table below for details.
• Undertake work Ensuring that any new systems work effectively, and that occupants (and future occupants) understand how to use them.
• Monitor and undertake necessary maintenance, upgrading systems where new technology emerges.
Consider minor intervention, behaviour changes and maintenance before more significant works to building fabric are proposed
Using ‘whole building approach’ –consider building use, construction type and environment. For traditional buildings, see STBA guidance*
Implement retrofit measures:
Provide advice to building occupants on their use and put monitoring systems in place
Identify and evaluate retrofit opportunities, which may incorporate measures as included in this SPD These shall follow the Circular Economy Design Principles Hierarchy** and for each measure benefits and impacts (including upon heritage significance) should be analysed, along with an identification of any technical risks.
Check heritage designations – is it a listed building or in a conservation area?
Undertake / commission assessment of heritage significance
Determine most appropriate approach and set this out in Sustainable Design Statement, and/or Retrofit Plan
Establish what permissions and consents are needed*** and associated information requirements (including Heritage Statement where heritage assets are affected)
Figure 22: The process for assessing retrofit opportunities * Sustainable Traditional Buildings Alliance (STBA) Responsible Retrofit Guidance
** See London Plan Guidance on Circular Economy Statements Hierarchy
*** See Table 13 Retrofit Permissions Required as a guide
9.2.3 Westminster retrofit opportunities
Advice is set out below on some of the opportunities for retrofit in Westminster. Please note that not all the measures below will be appropriate for all buildings. Equally, there may be some measures not listed below which may further improve the performance of a building, along with providing climate mitigation and adaptation benefits.
You should identify the most appropriate measures for your building based on the analysis recommended above, and using the advice on technical risks associated with different measures and impacts on heritage significance, where relevant. Lower risk measures should be considered first.
Further details on some of the suggested retrofit measures, heritage considerations and planning permissions required are included in Table 10.
BUILDING INSULTATION
Loft And Roof Insulation
Installing insulation in existing roof voids can have a significantly positive impact on energy efficiency. Historic buildings with a timber roof structure lend themselves to insulation between joists and rafters without any visual impact or harm to the historic building. Natural insulation materials such as wool-based insulation which allow a building to breathe should be used, reducing the possibility of moisture and damp problems. When fitting, an air gap must be left around the margins of the building to allow air to circulate. Care should be taken around electrical cables (lay these over the insulation) and allow a gap around any lights that may heat up (e.g. downlighters installed for the rooms below). It is also advised to insulate loft hatches.
Whilst insulation of a loft (between joists) is straightforward and is likely to be acceptable, insulation at rafter level (where a loft space has already been converted to provide additional space) is more complicated. There are various options including insulation between the rafters, on top of the rafters and below the rafters. Some options will result in the roof height changing. Additional considerations in listed buildings or unlisted buildings of merit in conservation areas may include whether there is a historically significant lining or ceiling fixed to the underside of the rafters. If this cannot be removed, and the only way to attach insulation is by removing the roof tiles and inserting from above, then this may not be economically feasible, unless other works to the roof are being undertaken at the same time. It is important that adequate ventilation is retained to avoid moisture build up and consequent damp problems.
For more information please see Insulating Floors in Historic Buildings
Floor Insulation (Suspended Timber Floors)
Heat loss through the floor amounts to around 15% for the average house. Simple draughtproofing of gaps between floor and skirting and between floorboards with sealant can be undertaken relatively easily and at low cost. Suspended timber floors on the ground floor, typical for many older properties can be insulated to improve thermal comfort. This will be quite straightforward if there is a cellar or crawlspace below, but without this, floorboards can be lifted and insulation inserted underneath, supported by netting. This should be to the depth of the joist only and should not block air bricks. Care needs to be taken when lifting
boards to minimise damage. Avoid blocking airbricks when draughtproofing or when insulating and take care to maintain cross ventilation beneath suspended timber floors to avoid rotting floor timbers. Consider the potential loss of historic fabric (floorboards/skirting/door surrounds/doors) that may occur if insulation increases floor height.
For more information please see Insulating Floors in Historic Buildings
Solid Wall Insulation
Solid wall insulation can be a way of improving the thermal efficiency of a building and could save energy and reduce energy bills. Most of the historic buildings in Westminster have solid masonry walls, either of brick or stone. The only way to insulate them is by adding a layer of insulation either internally or externally. Around 35% of heat loss from a typical home is through its walls.
External solid wall insulation systems consist of a layer of insulating material fixed to the wall and covered by a render or cladding, which provides a degree of protection from weather and impact damage. The major issue to consider is that external wall insulation will have an impact visually on the relationship between the building envelope and its openings, altering the detailing around windows and doors, and also eaves and roof verges. It is possible to extend roof eaves to deal with this.
For this reason, external solid wall insulation will need to be very carefully designed, and where heritage assets are affected, this is likely to be contentious. In these cases, it is likely to be allowed in certain circumstances such as on the rear elevations, and in enclosed locations, not for part-only of a unified terrace, although applications to apply to the whole of a terrace may maintain visual unity. Careful detailing is required around windows to minimise the impact of altered window reveals. This is generally considered a safer solution in terms of the risk of damp and moisture in a building than internal wall insulation and will not reduce floor space internally. However, there are also significant inherent risks in creating thermal bridges for moisture which can result in damp and rot problems in localised areas, so professional advice is necessary and very careful analysis of impacts on fabric would be needed and if acceptable, vapour permeable insulation should be used on traditional buildings
Internal wall insultation will take up internal floorspace and can alter the relationship of the door and window reveals, and will require any skirting boards, cornicing and decorative plasterwork to be relocated. There are also inherent risks in creating thermal bridges for moisture which can result in damp and rot problems in localised areas, and in many circumstances, it will not be appropriate on buildings of traditional construction. On such buildings, where internal insultation is demonstrated to be appropriate, materials with similar breathable qualities should be used.
For more information please see Insulating Walls in Historic Buildings.
Draughtproofing
Poorly fitting windows and doors, often the result of warping over time and years of repainting can lead to significant heat loss and make rooms feel uncomfortable. A significant amount of heat is lost through windows, both through the glass and from the gaps in and
around the frames. The heritage significance of a building will influence the options that are available, as alterations to windows and doors can impact historic significance.
There are a range of types of draught proofing systems available, from DIY foam strips which stick on, to professionally fitted compression seals or carrier seals that fit within frames and are suitable for different types of windows. Generally, foam strips, although very low cost, are not recommended for sash windows, and will need to be replaced regularly. Casement windows will be suitable for compression seals that sit within the window frame, and sash windows will typically have brush seals installed, which seal the gaps between top and bottom sashes when closed.
Generally, there will be no problem with fitting these to existing windows in historic buildings. For particularly noteworthy windows in listed buildings, it is advisable to check with officers before proceeding.
For more information please see Draught-proofing windows and doors
GLAZING
Secondary Glazing
Secondary glazing is available in a variety of systems to suit different window styles. Heat losses from a window could be reduced by over 60% by using secondary glazing with a low emissivity (Low-E) hard coating facing the outside. This also has benefits in terms of noise reduction. There are a variety of systems – those that are openable – hinged or sliding, fixed, and lightweight removable. In all cases, careful thought should be given to how to access original windows for cleaning and maintenance.
Secondary glazing will generally be possible for all types of historic properties, subject to obtaining listed building consent (where relevant). For best results it should be combined with a refurbishment of existing single glazed windows. However, draught- proofing should not be applied to the original window to maintain ventilation and avoid condensation. Double glazed secondary glazing may be an option particularly where noise is a significant issue. When considering the historic fabric of a building, secondary glazing is a lower risk option than replacing existing historic glazing with thermal single or double glazing as secondary glazing is reversible.
For more information please see Secondary glazing for windows and Westminster Retrofit How To Guide- Windows
Thermal Single, Double (Or Triple) Glazing
Use of energy efficient glazing and modern double-glazed windows can achieve improved thermal performance as well as security and acoustic benefits. There are slim profile options as well as those with low emissivity coatings which improve performance. These are appropriate in conservation areas, subject to detail and in some situations in listed buildings. Upgrading of existing historic windows to incorporate slim profile double glazing is also possible where this can be achieved without harm to significance. This will only be acceptable where windows are of types robust enough to accommodate the increased thickness and weight of double glazing without significant alteration. Thermal single glazing could also be acceptable where the existing window cannot be adapted to take double glazing. Where historic windows to a listed building contribute positively to special interest
and these cannot be upgraded without harm to significance, they should be retained, repaired and consideration given to draught-proofing and secondary glazing or other benign and reversible methods of upgrading to improve thermal efficiency.
For more information see Modifying historic windows – Historic England, Westminster Retrofit How To Guide- Windows and Passivhaus Retrofit
HEATING AND ENERGY
Efficiencies in heating can be made by reducing sources of thermal discomfort and by choosing to heat the people rather than the air (especially when local sources use low-carbon energy). For space heating and cooling, adjusting the thermostat can deliver great benefits. When boilers need to be replaced, low carbon equipment should be chosen. In this way, significant energy and carbon savings can be made without adverse effects on the fabric of the historic building, its character, or its setting.
Boiler Upgrade
Without proper programmable heating controls, the benefits of a more efficient condensing boiler will not be realised. Therefore, thermostats should be programmable ‘Chronoproportional’ thermostats on a timer, enabling a number of different programmable room temperature levels each day. These should be combined with TRV (Thermostatic Radiator Valves) in each room (except the room where the thermostat is located, and the bathroom) which switch off the heating in a room when it reaches the required temperature. Such systems can be wireless, which mean that no wiring or making good following works is required.
Ground And Air-Source Heat Pumps
Air source heat pumps take warmth from the air and use an evaporator coil to supply heating or hot water to a building. A system consists of an external unit, usually near a wall, though it can be located away from the building (requiring a clear amount of space either side for air circulation), and an internal unit with a hot water cylinder.
Ground source heat pumps consist of pipes underneath the ground which extract warmth to supply heating or hot water to a building. It consists of a loop of pipes filled with water and antifreeze, laid horizontally, in a trench or vertically (up to 100m deep). The fluid in the pipes warms up and passes through a heat exchanger in the heat pump converting it to high grade heat. To install ground source heat pumps requires a certain amount of space externally.
The installation of heat pumps on domestic premises are permitted development, meaning they don’t need planning permission, providing they meet certain conditions. However, homes with pitched roofs, listed buildings and those in conservation areas may require planning permission for heat pumps. Further information on permitted development criteria for heat pumps can be found on the Planning Portal website31 and residents are encouraged to contact the council to confirm whether planning permission is required before starting works.
Heat pumps are generally best suited to buildings with good insulation and airtightness levels. Heat pumps work better with underfloor heating, but radiators can be upgraded to
31 https://www.planningportal.co.uk/info/200130/common_projects/27/heat_pumps/2
accommodate the lower output from heat pumps. Heat pumps need to be accessible for maintenance and so retrofitting into high-rise blocks will require a suitable balcony, roof or communal area nearby or an internal ‘exhaust’ unit. Electric heat retention storage heaters could be considered as an alternative for properties that cannot have a heat pump installed.
For more information please see Heat pumps, Westminster Retrofit How To Guide – Air Source Heat Pumps and Passivhaus Trust – The Right Time for Heat Pumps
Solar Photovoltaic
Solar PV panels convert energy from the sun into electricity. The installation of PV panels can significantly reduce CO2 emissions and help to reduce energy bills. The orientation of the roof is the critical factor in determining maximum operational efficiency of solar PV panels. They should be as close to south facing as possible, and work best at an angle of 30˚to the horizontal. They should not be shaded by trees or neighbouring buildings.
An alternative to conventional solar PV panels is solar roof tiles, which are designed to look similar to normal slate roofing tiles. These may be appropriate where the roof is not original –as they would replace modern roof fabric. Where historic fabric is retained, solar panels would involve less loss of original roof tiles.
For more information please see Photovoltaics (PV) and Westminster Retrofit How To Guide –Solar Panels
Solar Thermal Panels
Solar thermal panels use the radiant heat of the sun to warm water in solar collectors which is pumped to a thermal store. It is most likely to be used to top-up or supplement a main system, rather than meet all of a building’s water heating demand. It is well suited to domestic buildings which have a low demand for hot water. The minimum amount of space needed to be effective is around 2-4m2, ideally between south east and south west facing, at an angle of 30˚ and should not be shaded by trees or neighbouring buildings. In addition to the collector panels, space is typically needed to house a large hot-water cylinder with a storage capacity of at least 120 litres, and up to 200-300 litres for larger buildings. Additional pipework will also be necessary.
There are different types of system, direct and indirect. Direct systems heat potable water in the collector panel and pump it to a tank for use. Indirect systems are filled with fluid (often antifreeze) which passes through the collector panel and a heat exchanger transfers heat to potable water which is separate from the fluid circulating in the panels. This slightly more complex system provides freeze and overheating protection.
For more information please see Westminster Retrofit How To Guide – Solar Panels
GREENING
The retrofitting of existing buildings can bring about opportunities to enhance greening measures. This can help to contribute to the conservation and enhancement of biodiversity, along with enabling green corridors and facilitating habitat creation.
This can also be beneficial in managing flood risk by attenuating rainwater, reducing the likelihood of flooding from surface water runoff. Greening measures may also act to reduce overheating (and reduce the urban heat island effect), reduce carbon emissions, absorb noise
and trap air pollutants. Further information on the type of green infrastructure which could be included in retrofit proposals, see the ESPD section on Greening and Biodiversity. The nature of existing buildings and the type of greening measures proposed will need to be reviewed on a case-by-case basis. For example, by incorporating a green roof which may be a heavier, more intensive roof, this may require greater load bearing capacity, which could be less achievable on historic buildings. Additionally, there may be several fire safety considerations which must be accounted for in the design and installation of living wall systems. Key risks include the combustibility of the planted biomass, which requires consistent irrigation and maintenance to reduce the potential for ignition and fire spread. Additionally, certain living wall designs incorporate extensive combustible plastics within potting, irrigation, and drainage systems, which may pose fire safety risks.
9.2.4 Retrofitting Guidance for Householder Applicants
There are a growing number of resources to assist residents in making their homes more energy efficient and reducing their environmental impact. The key elements of retrofit include:
1. Reduce the heating demand and energy use;
2. Remove fossil fuel heating and cooking sources and replace with low carbon alternatives; and
3. Generate renewable energy on site if feasible.
The council’s website provides useful resources and advice for residents on climate change, energy efficiency and wider sustainability opportunities.
The Planning Portal has information on planning rules, permitted development limits and building regulations for common projects for the home. Most energy and water efficiency initiatives for domestic properties, such as draught-proofing, insulation, renewable energy installations and butts for rainwater harvesting are permitted development, but residents in listed buildings or conservation areas should check Table 10: Retrofit Measures below for further guidance.
EcoFurb provides a low carbon homes service that helps homeowners plan and deliver energy efficiency improvements, gives impartial advice, and oversees the works. London residents can also use the free Plan Builder on their website to get ideas on how to retrofit your individual home.
LETI’s Climate Emergency Retrofit Guide provides advice on how to develop a whole house Retrofit Plan. It also provides best practice targets for constrained (e.g. listed buildings) and unconstrained building types. The Passivhaus Trust also has guidance on their EnerPHit Retrofit Plan
There are a number of useful resources for residents wishing to upgrade their historic homes including the council’s webpages on Retrofitting historic buildings, Design and heritage in planning and Planning householder retrofit how-to guides as well Historic England’s online resources for Energy Efficiency and Retrofit in Historic Buildings and the Sustainable Traditional Buildings Alliance (STBA) Planning responsible retrofit of traditional buildings
9.3 Development Requirements
9.3.1
Information
SUSTAINABLE DESIGN STATEMENT
Sustainable Design Statements are an adopted validation requirement for all applications which create new floorspace and/or where extensive works to retrofit/improve the environmental performance of a building are proposed. This includes householder applications. Applicants are encouraged to include a Retrofit Plan, as set out above. Where heritage assets are affected, the Retrofit Plan and Heritage Statement32 should set out how the proposed changes may impact on a building’s heritage significance and address the balance between heritage harm and public benefit in line with relevant paragraphs of the NPPF and City Plan Policy 39. This should demonstrate that harm has been avoided in the first instance and, where harm is caused, demonstrate that the least harmful option is being pursued, and justify that the proposed solution improves building performance. Applicants are encouraged to demonstrate how any proposed changes are delivering a public benefit in delivering exemplar schemes to mitigate and adapt to climate change and achieving standards beyond policy compliance.
Additional guidance on Sustainable Design Statements for different development types are available online33. This includes for:
• Small Scale Residential Schemes (5 units or less)
• Medium Size Non-Domestic Schemes (500sqm – 1,000sqm GIA) and Residential buildings (5 – 10 units)
• Major Non-Domestic Schemes (>1,000sqm GIA) and Residential schemes (10 or more units)
9.3.2
Standards
LETI CLIMATE EMERGENCY RETROFIT GUIDE
All developments involving retrofit of existing buildings are encouraged to consider the design principles set out within the LETI Climate Emergency Retrofit Guide. These represent industry best practice and go beyond the fabric performance of BREEAM domestic refurbishment, driving better retrofitting outcomes.
32 Where the Heritage Statement is being used to provide details on the impacts upon historic buildings, cross-references shall be made within the Sustainable Design Statement.
33 Please note, these are currently being updated and will be available online in due course. Following consultation on the ESPD, these links will be updated in the final version.
UK NET ZERO CARBON BUILDINGS STANDARD
Whilst the UKNZCBS is currently in Pilot, once it is adopted, the council will support development proposals which align with the requirements set out in the Standard. This includes specific requirements for retrofit projects.
HOMES ENGLAND ADVICE NOTES
In July 2024, Historic England published an Advice Note34 on Adapting Historic Buildings for Energy and Carbon Efficiency. The Advice Note provides further guidance on the need to retrofit historic buildings in the context of the climate emergency, along with guidance on permissions and decision-making processes. A range of common interventions to historic buildings are reviewed in detail within the Advice Note, from works to listed buildings, to insulation and new energy technologies. The Advice Note should be read in conjunction with other online resources from Historic England on Energy Efficiency and Retrofit in Historic Buildings
STBA RESPONSIBLE RETROFIT GUIDANCE
The STBA Planning Responsible Retrofit of Traditional Buildings provides further guidance on how the retrofitting of buildings can be done in a way that reduces the energy consumption of buildings, whilst also maintaining building fabric, heritage and the health of building occupants. The guidance promotes a ‘whole building approach’ which integrates building fabric, services (such as heating and ventilation) and human behaviour with the context of existing buildings.
DETAILED PRACTICAL CONSIDERATIONS
34 Historic England Advice Note 18 (HEAN 18)