Drip Edge Installation in North Carolina: Eaves vs Rakes Overhang Rules
The answer to whether underlayment or drip edge goes on first depends on whether you are working on the eave or the rake.
On eaves (the bottom horizontal gutter edge), metal drip edge goes on first, directly against the bare wood decking, with underlayment installed over the top of the metal flange. On rakes (the sloped gable edge), underlayment goes on first, and drip edge is installed over the underlayment. Reversing this sequence allows wind-driven rain to blow underneath underlayment on eaves or seep under metal on gables.
The 1/4 to 3/4-Inch Shingle Overhang Rule
Asphalt starter shingles must overhang the metal drip edge by 1/4 to 3/4 inch (1/2 inch is standard AGCS practice). Cutting shingles flush causes capillary surface tension that draws water backward under the bottom shingle course, rotting the fascia. Overhanging more than 3/4 inch leaves shingles unsupported, leading to wind blow-offs.
Building Code Mandate
Under NCRC Section R905.2.8.5, drip edge flashing is mandatory on all eaves and gable rakes of asphalt shingle roofs. The vertical drop leg must extend at least 1/4 inch below fascia wood, and adjacent sections must overlap by a minimum of 2 inches.
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