Which option correctly restates the rule for alternate courses?

Which option correctly restates the rule for alternate courses?

• A. There should be no direct alignment of joints
• B. Alternate courses must have a 1-1/2 inch sidelap
• C. Adjacent courses require no sidelap
• D. All joints align on alternate courses

Answer: (A)

Joints from one course must not line up with joints from the course above or below. The idea is to create a staggered pattern so there isn’t a continuous seam running up the roof, which improves watertightness and wind resistance. When alternate courses are laid, the seams are offset so water isn’t able to follow a single vertical path through a long joint. This is why statements about a fixed sidelap or about adjacent courses not overlapping don’t fit; those either add an unnecessary specific measurement or imply improper overlap. And the idea that all joints align on alternate courses would defeat the purpose of staggering.

Joints from one course must not line up with joints from the course above or below. The idea is to create a staggered pattern so there isn’t a continuous seam running up the roof, which improves watertightness and wind resistance. When alternate courses are laid, the seams are offset so water isn’t able to follow a single vertical path through a long joint.

This is why statements about a fixed sidelap or about adjacent courses not overlapping don’t fit; those either add an unnecessary specific measurement or imply improper overlap. And the idea that all joints align on alternate courses would defeat the purpose of staggering.