the slate used and how well they are maintained. The material itself deteriorates only slowly and may be recycled from one building to another.

The primary means of failure in a slate roof is when individual slates lose their peg attachment and begin to slide out of place. This can open up small gaps above each slate. A secondary mode of failure is when the slates themselves begin to break up. The lower parts of a slate may break loose, giving a gap below the slate. Commonly, the small and stressed area above the nail hole may fail,