01
More headlap means less exposure
For the same slate length, a 3-inch headlap produces one-half inch less exposure than a 2-inch headlap. That adds courses and pieces over the roof area, affecting quantity, weight and labor.
02
Do not choose by price alone
A proposal with greater exposure may appear to use fewer slates, but it may also provide less overlap than the project requires. Compare bids using the same headlap, slate dimensions and roof-area assumptions.
03
Use project-specific criteria
Steeper slopes and protected conditions behave differently from lower slopes exposed to wind-driven rain or ice. Follow the applicable standard, design professional and system guidance rather than applying one headlap to every roof.