Shingle Exposure and Offset

Two layout rules govern how asphalt shingles are laid: exposure and offset. Exposure is the part of each course left visible to the weather. Offset (also called stagger) is the sideways shift of each course so that joints and cutouts do not line up vertically from one course to the next.

Exposure

Exposure is set by the shingle size and the manufacturer. Typical exposures are 5 in (127 mm) for traditional 12 x 36 in shingles and 5 5/8 in (143 mm) for "metric" 13 1/4 x 39 3/8 in shingles. Canadian guidance describes the relationship between exposure and headlap: each course laps the one below by the exposure plus a headlap that is typically 50 mm (2 in). Variable-butt and designer shingles use their own exposure rules.

Exposing shingles too much reduces the headlap and can leave nails uncovered; too little wastes material and changes the appearance.

Offset

The goal is that a joint or cutout in one course always sits over solid shingle in the course below. Common approaches:

• Stair-step (diagonal) method. Each course starts a set distance further along than the one below, repeating after several courses. For traditional 3-tab shingles a 6 in (152 mm) step is common.
• Straight-up (racking) method. Shingles are laid in vertical columns, alternating full and shortened shingles. Canadian guidance alternates full shingles with shingles cut 150 mm (6 in) shorter.
• Random offset. Many laminated shingles allow variable offsets within a minimum set by the manufacturer.

Canadian guidance warns against any layout where joints in successive courses are closer than 100 mm (4 in).

Chalk lines

Roofers snap horizontal chalk lines every few courses to keep exposure even and vertical lines at the shingle length to keep offsets regular across large or broken roof planes. Valleys, dormers and hips are where layouts most often drift.