Drip Edge Guide

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What Drip Edge Is and Why It Exists

Drip edge is formed metal that covers the edge of the roof sheathing. The vertical leg hangs slightly below the deck so water drips clear of the fascia instead of wicked back under the sheathing. The horizontal flange sits on the deck and gets covered by underlayment and/or shingles, depending on the edge type.

Without it, water can soak the exposed plywood edge, rot the fascia, and stain the eave. Wind can also drive rain under the first course when the edge metal is missing or installed in the wrong lap order.

2018 IRC §R905.2.8.5 — The Spec Numbers

For asphalt shingles, the 2018 IRC requires drip edge at eaves and rakes with these minimums:

• 1/4 inch below the roof sheathing (so water clears the wood edge)
• 2 inches of flange overlap onto the deck
• 3 inches of overlap at end joints between pieces
• Fastened at maximum 12 inches on center

Those same numbers drive the calculator’s usable coverage: a 10-ft stock piece minus 3 in (0.25 ft) of end-joint overlap leaves about 9.75 ft of run coverage per stick.

Install Order: Eaves vs Rakes (The Part People Mix Up)

This is the most common point of confusion on shingle roofs:

• At eaves: install drip edge first, then lap the underlayment over the drip-edge flange. Water running down the roof plane hits the underlayment, then the metal, then drips into the gutter.
• At rakes: install underlayment first (or keep it continuous to the rake edge), then install drip edge so the metal flange laps over the underlayment. That keeps wind-driven rain from getting under the metal and behind the underlayment at the gable edge.

Why the Lap Order Reverses

Gravity and wind attack the two edges differently. At the eave, the dominant load is water flowing downslope. You want a continuous underlayment path that dumps onto the drip edge and then into the gutter — so the underlayment must cover the flange.

At the rake, the dominant load is often wind-driven rain pushing sideways under the edge metal. If the underlayment sits on top of the rake drip edge the way it does at the eave, wind can drive water under the metal flange and under the underlayment edge. Putting the metal on top of the underlayment at the rake closes that path.

Ice & water shield at cold-climate eaves follows the same eave logic: the membrane typically laps over the eave drip edge. Size that band with the ice & water coverage calculator and keep the drip-edge flange in the stack correctly.

Takeoff Basics

Measure every eave and every rake that receives metal. Add them for total linear feet. Stock is usually sold in 10-ft pieces; account for the 3 in joint overlap and round up. On runs over ~40 ft, buy one extra stick for cuts and corners. The calculator does that math. Shingle field coverage is separate — use the shingle bundle calculator.

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