Guidance identifies the changes that are most likely to be given the thumbs up when approvals are required through the planning process
An advice note issued by Historic England has identified the low carbon interventions to heritage buildings that are likely to be considered acceptable in most cases, when approvals are required through the planning process.
Adapting Historic Buildings for Energy and Carbon Efficiency: Historic England Advice Note 18 was drawn up by the government's statutory adviser on the historic environment for use by local planning authorities, heritage consultants and others involved in the planning process. It is applicable to all listed and unlisted building types, apart from places of worship, which are not managed through listed building consent.
The advice on acceptable changes to historic buildings focuses primarily on energy efficiency and solar energy generation, but does not cover every eventuality and, according to Historic England, decisions must be made on a case-by-case basis, ideally based on specialist, professional advice.
Windows
On the subject of upgrades to windows, draught-proofing will almost invariably be acceptable, says Historic England, and ‘can usually be achieved with only a negligible effect on a building’s special interest’. Rare exceptions might include windows of exceptional delicacy, or which cannot be unobtrusively draught proofed, harming the building’s special interest.
Installation of secondary glazing to windows or slim-profile/vacuum double-glazing within historic frames will generally be acceptable. In the case of the latter option, original glazing bars should be retained, and windows simultaneously refurbished and draught-proofed to benefit fully. Sash windows may require heavier weights to balance the increased weight of the glass.
The advice note states that double-glazed windows ‘of appropriate material and pattern’ can be used to replace windows that do not contribute to the architectural or historic interest of a building and will generally be acceptable.
Roof insulation
Turning to insulation upgrades, Historic England notes that loft insulation will generally be acceptable is unlikely to affect the special interest of the building, but not when spraying adhesive foam insulation to the underside of the roof covering, which is likely to harm the fabric of the building and is not easily removed.
Insulation within the roof plane ‘is acceptable in some cases’, the document states, often above, between or below the rafters, but not in cases that would require the loss of historic plasterwork or obscure significant elements of the roof structure. Listed building consent is normally required for this.
Floor insulation
Insulation between or under floors is generally acceptable with certain considerations, says Historic England. For example, insulation within the floor void should not change floor levels or create ‘undue harm to any historic floor surfaces’. Underfloor insulation, such as where a timber ground floor is suspended over bare earth, should be avoided if the underfloor layer or finishes are particularly significant and directly impacted by the works.
In addition, insulating under solid floors may not be appropriate where surviving historic floor surfaces or other archaeological remains exist ‘just under the current floor, or where shallow foundations could be compromised’. Listed building consent may also be required for these alterations.
Internal wall insulation will be acceptable ‘only in some cases’, the advice note states, because it will generally disrupt the character of historic interiors, including finishes, such as plaster, joinery, cornices, and chimneypieces. Previously unplastered internal walls could be lined with insulation as part of a conversion; appropriate and listed building consent is almost always required for this.
External wall insulation
The external appearance of listed buildings is a key concern and for this reason external wall insulation is unlikely to be acceptable due to harmful impacts. The installation of insulation within external walls will be acceptable in some cases: for example where the historic infill has been replaced with modern materialsit may be appropriate to renew the infill with insulation. Similarly, insulation could be inserted between the outer cladding and internal plaster of weather-boarded houses, or other historic buildings with external cladding, ‘provided an air gap is maintained and detailing can mitigate moisture risk’.
Where ‘there is clear evidence’ that a listed building was originally intended to be rendered, reinstatement of historic render finishes will improve thermal performance, says Historic England, and ‘is almost invariably desirable’.
Cavity walls in post-Second World War buildings are considered a good opportunity for invisible, cheap and quick to install insulation, with no reduction of room sizes.
Energy systems
Swapping fossil fuel boilers, heating and hot water systems for low carbon alternatives such as heat pumps is a key to the UK’s transition to net zero, and in the case of historic properties it will generally be acceptable, says Historic England.
The impact of heat pumps can generally be minimised through ‘careful siting, design and screening”, although routing pipework may damage historic fabric and listed building consent is normally required because they are fixed to a building.
Turning to photovoltaic and solar thermal panels, Historic England says these will be acceptable in some cases, but have the potential to ‘be visually incongruous and harm a building’s architectural qualities’.
Designers therefore need to consider the aesthetic impact of panels on significant views of the building and the impact of the additional weight of panels on the roof, as well as weather-tightness and risks of fire.
According to the advice note, planners generally frown upon panel installation on principal roof slopes, but installation on less prominent roof slopes will usually be acceptable, even if visible, potentially with the exception of Grade I- and II*-listed buildings. The preferable option is to mount them on outbuildings or land associated with a listed building, rather than on the building itself, provided they are not of greater prominence.
The installation of solar slates to replace existing roof coverings will be acceptable in some cases, but not on prominent roof slopes because they ‘do not usually convincingly replicate the look of traditional slates’.
Buildings remain the UK’s second highest carbon-emitting sector, accounting for 17% of total UK operational emissions in 2022, and around a quarter of the building stock is at least 100 years old. According to Historic England, heritage buildings must be adapted ‘not only to support the transition to a Net Zero society, but also to improve energy/cost-efficiency and thermal comfort for occupants, and to ensure they remain safe, desirable and viable assets for future generations to enjoy’.
The organisation intends to publish further advice on integrating historic environment and climate change strategies through local plan making, wind energy generation, and places of worship.
Adapting Historic Buildings for Energy and Carbon Efficiency: Historic England Advice Note 18