When buying a Listed Building, it is absolutely essential that consideration for the legal status of all alterations, however minor, is done before you commit to the purchase. Common alterations might be changing the use of a room, installation of an en-suite, replacement windows, walls taken out or put in, anything to do with floors, fireplaces, stairs and other such architectural details. It is not only related to extensions or roof conversions. It is not true to believe that only the front or outside is Listed. The whole building is Listed – inside and out. When unauthorised alterations are found you should seek legal advice on the significance and what to do next.
If you own the house already, you should always seek professional advice from a Conservation Accredited Building Surveyor, Architect or Structural Engineer before you make any alteration to the building. An application for Listed Building Consent will be required.