How much of the slate shows?
The portion of the slate that you can see, (not buried under succeeding courses) is referred to as “exposure”. Exposure is dependent on the headlap and calculated by: (length minus headlap/ 2). Diagram For example, an 18″ tall slate will have an exposure of 7-1/2″. [(18″ minus 3″) divided by 2] = 7-1/2″.