I have a sandstone bay which is double glazed. The double glazing is coming to the point of needing replaced, however, I have a thin green coat at some points on the outside bay and one of the sandstone columns is starting to discolour. I understand this is a common problem but am terrified I have rising damp. We have block paves in the front garden but I have checked the area between the pave and the window and there seems adequate space to allow for water drainage. Could you advise me please?