there are damp patches in both bedrooms where the chimney stacks are and is particularly noticeable after rain. Had flashings,lead gutter replaced as well as pointing but the walls are still damp. roofer suggests that the chimneys have 'broken its back' , where the slate that runs through the stack has broken down letting water run down the stack and hence the damp bedroom walls. is this a common term or is he feeding me a load of bs? is there a way of reparing this w'out rebuilding stacks