01
Use the actual headlap requirement
Do not assume the longer slate permits any desired exposure. Subtract the specified headlap and divide by two to find nominal field exposure.
02
Estimate by square-inch coverage
Multiply actual width by exposure to find theoretical coverage per piece. Divide 14,400 by that number, then apply allowances for non-field conditions.
03
Coordinate top and bottom courses
The under-eave and top-course dimensions should be planned before installation. Long field units do not eliminate the need for special terminal pieces.