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 : straight-up method, half-pattern, 4-in. offset, and 5-in. offset. The 5-in.-offset pattern provides the best all-around protection.
Alignment Guides. Most three-tab asphalt shingles include 1/2-in. alignment slits across the top edge and half-slots along the edges. Use these to line up adjacent shingles and successive courses. In addition, shadow marks may run the length of each shingle near the top of the slots. These are meant as an aid to horizontal alignment.
A half pattern (also called half-tab or sixes) staggers each course with a 6-in. offset (half a tab width for metric shingles). Butt joints are better protected from water migrating horizontally, but cutouts still align every other course.
A 4-in. offset keeps cutouts separated by two courses, and butt joints align every ten courses. But the short lap doesn’t provide enough protection in wet climates, or in areas with severe freeze-thaw cycles.
A 5-in. 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 as well.
For more on installing asphalt shingles, including laminated “Architectural” styles, visit the JLC Field Guide.