How much drip edge do I need, and do I need it at all?

Step 1: Measure the edges

• Eaves. The horizontal bottom edges where gutters hang.
• Rakes. The sloped edges at gable ends. Measure along the slope, not the horizontal width, since a sloped edge is longer than the wall below it.

A measurement report from aerial imagery usually lists eave and rake lengths separately, which is the easiest source.

Step 2: Do the math

Each 10-foot piece covers slightly less than 10 feet because adjacent pieces must overlap at least 2 inches. Divide the total length by about 9.8 feet, round up, then add roughly 10 percent for outside corners, cuts at the rake peaks and mistakes. For example, a ranch house with 120 feet of eave and 80 feet of rake has 200 feet of edge, which works out to about 21 pieces before waste, so plan on around 23 or 24.

Step 3: Pick the right profile

• L-style or T-style drip edge for rakes.
• T-style or gutter apron at the eaves, depending on how the gutters sit.
• Matching colors to the fascia or gutters if the edge is visible.

Why it is not optional

Drip edge supports the shingle edge, throws water clear of the fascia and into the gutter, and closes the gap that wind-driven rain and insects use. Code also specifies how it goes on: extending at least a quarter inch below the sheathing, at least 2 inches back onto the deck, fastened at no more than 12 inches apart, with underlayment over the metal at eaves and under it at rakes. See drip edge explained and how roofers measure a roof.