Water has been dripping from the ceiling at the back of this dormer. To resolve the problem we stripped out the slate to get to the root of it. We sealed the board at the bottom of the pitched roof & the gulley to the flat dormer roof in one piece & carried out a repair to the under felt using breathable membrane. We re-pointed the failed mortar on the ridge line. Finally we put back the slates, replacing any that were broken/damaged & also installed an extra course of slate to ensure that no water gets in. We have left a gap in the bottom course to allow for the protruding main rafter. In the past slates had been forced into this gap. The pressure exerted on these slates meant that over time they cut into the under felt & eventually snapped.