In reference to the roof of a property, the Verge is the edge of a gable roof, where the tiles of the gable roof meet the gable end wall. The roof verge acts as seal to hold the tiles in place, so it is important that this element of the roof is well maintained.
As with many external parts of a house, the mortar of the roof verge will deteriorate over time, particularly in wet and freezing conditions. If cracks appear in the mortar, or it starts to crumble, action must be taken. The damage will quickly worsen, and will soon compromise the structural integrity of the roof.