01
Break the vertical joints
The joints in one course should be offset from those in the course below according to the accepted layout. Uniform-width slate commonly creates a regular broken bond; random-width work requires active sorting and planning.
02
Watch narrow pieces
Small cut pieces beside valleys, walls, penetrations or rakes can reduce side lap and create weak fastening locations. Adjust the surrounding layout rather than forcing a sliver into a critical drainage area.
03
Mark the roof before production
Chalk lines and control marks help maintain course alignment and joint relationships. Layout should anticipate dormers and penetrations so the crew is not improvising inadequate offsets when it reaches them.