The exemption is laid out in guidance written by English Heritage for the government, to be published at the end of May.
This states that a lower thermal performance is permissible if the extension is “in keeping” with the rest of the building.
It also exempts replacement windows, doors and walls on historic buildings. It says: “The right balance is needed between reducing energy use and greenhouse emissions, and conserving the national and local heritage.”
John Fidler, head of historic buildings conservation at EH, said: “What we’ve managed to do is get into Part L a degree of flexibility for historic buildings that enable specifiers to preserve fenestration and historic features.”
If the original draft of Part L had been applied, historic buildings such as Buckingham Palace would have to have PVCu windows installed when existing ones were replaced.
In the guidance, historic buildings include all those in conservation areas and those defined as of architectural interest in local authority plans.
The guidance note is aimed at designers, local authority building control officers and conservation officers who are responsible for the implementation of Part L where it affects historic buildings. It will strengthen the hand of conservation officers reluctant to change the character of historic buildings for the sake of reduced energy use.
The guidance identifies areas of conflict between Part L and heritage conservation and offers compromises that include the following:
- Insulation to pipes and ducting may be restricted for the sake of appearance, access or space.
- Heat loss from pipes and ducts may be permitted if access is difficult or the installations are of historic interest.
- Providing energy-efficient space heating and hot water may be difficult if historic equipment is to be conserved.
- Air-conditioning installed in historic buildings may be less efficient owing to restrictions placed on appearance, access or space.
