Policies for the identification and protection of historic buildings and conservation areas are set out in 'Planning Policy Guidance 15: Planning and the historic environment' published by the Department of Communities and Local Government
Listed buildings are those that have been selected for special architectural or historic interest.
Grade I buildings are of exceptional interest
Grade II* are particularly important buildings of more than special interest
Grade II are buildings of special interest, warranting every effort to preserve them.
More than 90% of listed buildings are Grade II.
English Heritage has a statutory role in the planning system. It is the Government's lead advisory body for the historic environment and will provide advice to local planning authorities and government departments on any development proposals that affect listed buildings and conservation areas, but in most cases this will only be for plans that could cause significant damage or involve buildings of national importance.
Annex C of PPG 15 provides comprehensive guidance on alterations to Listed Buildings.
Guidance on Listed Building Windows
The guidance for windows is that they should be repaired if at all possible but both draught proofing and the inclusion of secondary glazing can be an acceptable enhancement as they are reversible adaptations.
If the window is beyond repair a replica single glazed replacement window is acceptable and this can then be thermally enhanced with a secondary window.
guidance on windows in Conservation Areas
Conservation Areas are described as 'areas of special architectural or historic interest the character or appearance of which it is desirable to preserve or enhance'. They are covered by the Planning (Listed Buildings and Conservation Areas) Act 1990. Conservation area consent is required for demolition or any work that affects character of the area and advice should be obtained from a Conservation Officer.
The installation of secondary glazing should not require consent unless the building is listed in which case Listed Building Consent should be sought.
VAT relief for alterations to Listed Buildings was removed with effect from 1st October 2012. However applications made prior to 21st March 2012 which gained approval will continue to benefit from zero rating until 20th September 2015.
Further guidance on heritage issues can be obtained from:
The Society for the Protection of Ancient Buildings
The Georgian Group
The Victorian Society