The guideline for alternate courses best described by which statement?

The guideline for alternate courses best described by which statement?

• A. There should be no direct alignment
• B. Sidelap must be 1-1/2 inches
• C. Joints must align on every third course
• D. Joints must align on all courses

Answer: (A)

Joints in alternate courses must be offset so they don’t line up from course to course. This staggered arrangement is essential because it breaks up vertical seams that could create a continuous weak line from the eave to the ridge. When joints don’t align, water intrusion paths are disrupted and wind resistance improves, since no single seam is carrying the load straight up through every course. In asphalt shingles, you typically offset by at least a practical amount (often about half a shingle or more, depending on the product) to maintain this staggered pattern. If joints lined up on every course, or on every third or all courses, you’d create predictable weak points and increased potential for leaks or wind damage. A roof that keeps joints from aligning across courses offers better durability and weatherproofing.

Joints in alternate courses must be offset so they don’t line up from course to course. This staggered arrangement is essential because it breaks up vertical seams that could create a continuous weak line from the eave to the ridge. When joints don’t align, water intrusion paths are disrupted and wind resistance improves, since no single seam is carrying the load straight up through every course. In asphalt shingles, you typically offset by at least a practical amount (often about half a shingle or more, depending on the product) to maintain this staggered pattern. If joints lined up on every course, or on every third or all courses, you’d create predictable weak points and increased potential for leaks or wind damage. A roof that keeps joints from aligning across courses offers better durability and weatherproofing.