Should shingles overhang the roof?

Yes, shingles should definitely overhang the roof edge, and proper overhang is critical for correct water shedding and to prevent damage to fascia and decking. Building codes and manufacturer installation instructions require a specific overhang. At the eave edge where gutters are located, asphalt shingles should overhang the drip edge by 1/4 inch to 3/4 inch, typically about 1/2 inch. This small overhang ensures water drips into the gutter rather than running back under the shingle and behind the fascia, which would cause wood rot. At the rake or gable edges, shingles should also overhang the drip edge by 1/4 to 3/4 inch to protect the edge. Too little overhang allows water to wick back under and damage the deck edge, while too much overhang, more than 1 inch, makes the shingle vulnerable to wind uplift and breakage, as the unsupported edge can snap off in high winds or under ice load. Professional roofers achieve consistent overhang by snapping chalk lines and using a drip edge flashing that extends slightly beyond the deck. The starter strip at the eave should also overhang slightly to provide a straight edge for the first course. Proper overhang is inspected during quality installations.