agree Penny....I think this is what I find so frustrating about the "listing" process.....for example...If a property doesnt become listed until the mid 80's, its possible that many old, original period parts of a property could have already been updated legally....i.e an original period sash window to a UPVC replacement and as it was done before the property became "listed" the owner at the time didnt do anything wrong. I guess the problem then becomes if a property had a double glazing window in place at the time of listing, would the CO still be happy to allow a "like for like" replacement? My listed details are very limited and just mention 2 sash windows and I'm glad to say they are all still in place but I do find the whole "listed building" process to have many grey areas....I personally prefer to repair, than replace but it still causes me to scratch my head when its mentioned that a "whole" property becomes listed, when clearly there are parts that are no longer original and havent been since long before it was added to the historical register...