If flats or commercial buildings are within a conservation area the Local Planning Authority will seek to retain historic windows wherever possible or to allow only like for like replacement. The retention of historic fabric will always be the primary consideration when considering applications for replacement of windows in listed buildings. Please note: Part L Building Regulations allows for single glazing to listed and historic buildings in conservation areas.
The link below is a highly informative document produced by English Heritage called Energy Efficiency and Traditional Buildings 2007. Details are contained within this document on benign methods of improving energy efficiency in historic buildings such as adding draught strips to historic windows and appropriate methods of insulation.
English Heritage - Climate Change and your home
English Heritage - The importance of windows
SPAB Advice Leaflet - Timber Windows
