Offset patterns for asphalt shingles
by Dave Flickinger, RRO
Each month in this column, one of NRCA's technical services staff members will answer readers' technical questions. If you have a specific question you would like answered in this column, send it to Professional Roofing magazine, 10255 W. Higgins Road, Suite 600, Rosemont, IL 60018-5607.
Q: What is the purpose of an offset pattern for three-tab asphalt shingles, and what are common patterns?
A: An offset pattern's purpose is to create a consistent stagger between shingles' side joints from one shingle course to the next. An offset pattern prevents shingle side joints from aligning with side joints in adjacent courses. Side joints that are near or align with joints in a previous course negatively can affect a steep-slope roof system's watershedding ability.
The most common offset patterns are known as 4-, 5- and 6-inch patterns. Each offset pattern creates a specific pattern for three-tab shingles' cutouts and has a distinct appearance.
For the 4-inch pattern, shingle cutouts align every third course. Every seventh course in the 5-inch pattern is aligned; and every other course in the 6-inch pattern is aligned.
An offset pattern is begun with a full-width shingle, typically at the left-hand side of a roof eave with subsequent shingles offset to a specific dimension and stacked diagonally (see figures). The first shingle group (as shown in the figures) is referred to as a "book." Shingle installation proceeds away from a book.
For the 4-inch pattern, the second shingle is installed above the first full-width shingle and offset 4 inches (102 mm). Each subsequent shingle is offset 4 inches (102 mm) and installed above the previous shingle until the book is complete.
4-inch pattern
For the 5-inch pattern, the second shingle is installed above the first full-width shingle and offset 5 inches (127 mm). Each subsequent shingle is offset 5 inches (127 mm) and installed above the previous shingle until the book is complete.
5-inch pattern
For the 6-inch pattern, the second shingle is installed above the first full-width shingle and offset 6 inches (152 mm). Each subsequent shingle is offset 6 inches (152 mm) and installed above the previous shingle until the book is complete.
6-inch pattern
If metric-sized shingles are used, the 4-, 5- and 6-inch offset patterns typically are modified as follows: The 4-inch pattern is installed using multiples of 4 3/8 inches (111 mm); the 5-inch pattern is installed using multiples of 5 5/8 inches (143 mm); and the 6-inch pattern is installed using multiples of 6 9/16 inches (167 mm).
Which offset pattern a roofing contractor uses typically depends on regional preference. It should be noted that some nonstandard shingles may require specific offset patterns determined by their manufacturers.
Dave Flickinger is an NRCA manager of technical services.
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