How well three-tab shingles hold up over time depends to some degree on the patterns used to lay them. Although many customers prefer to see the cutouts aligned on the roof, this directs runoff into channels that erode the shingle surface.
There are four basic patterns to laying out three-tab shingles: straight-up method (A), half-pattern (B), 4-inch offset (C), and 5-inch offset (D). The 5-inch offset pattern provides the best all-around protection. —Excerpted from JLC Field Guide to Residential Construction, published by JLC Books (JLConline.com), a division of Hanley Wood, LLC.
A. STRAIGHT-UP METHOD The straight-up method of laying shingles offsets alternating courses 6 inches from a vertical line up the roof (half a tab width for metric shingles). The alignment of butt joints and cutouts in every other course, however, can cause premature weathering of surface granules.
B. HALF-PATTERN A half-pattern (also called half-tab or sixes) staggers each course with a 6-inch offset (half a tab width for metric shingles). Butt joints are better protected from water migrating horizontally, but cutouts still align every other course.
C. 4-INCH OFFSET A 4-inch offset keeps cutouts separated by two courses, and butt joints align every 10 courses. But the short lap doesn't provide enough protection in wet climates, or in areas with severe freeze-thaw cycles.
D. 5-INCH OFFSET A 5-inch offset provides the best all-around protection. Both the cutouts and the butt joints align only every eight courses, so runoff is less likely to cut channels into the shingle granules. It also hides shingle irregularities.