01
Pitch changes the exposure to water
Water drains more slowly on a lower slope and is more vulnerable to wind-driven movement, ice and capillary effects. A detail suitable for a steep roof should not be assumed to work unchanged near a minimum slope. The applicable standard, code, design professional and slate-system guidance should control.
02
Headlap and exposure are linked
Increasing headlap reduces the exposed portion of each slate and changes the course layout and quantity. The roof must be planned from eave to ridge so the selected exposure can be maintained without creating short laps or awkward top courses.
03
Transitions deserve special attention
Porches, shed roofs, cricket areas and low-slope sections connected to a steeper slate roof may require a different roof system or specially designed transition. Underlayment alone should not be used to justify a slate layout outside accepted limitations.