Offsets for Three-Tab Shingles
There are four basic patterns to laying out three-tab shingles: 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 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.
Offsets for Laminated Shingles
Follow manufacturer instructions to determine shingle offset to avoid alignment of joints. Avoid pieces narrower than 6 inches at rakes, and don’t drive nails closer than 3 inches to the roof edge.