Drip edge and flashing basics
The metal edges and joints of a roof are small line items on an estimate but outsized in importance — they are what keep water out at the most leak-prone spots. Here is what they are and how to account for them.
What drip edge does
Drip edge is the metal trim installed along the eaves and rakes. It directs water off the roof edge and into the gutter rather than letting it wick back under the shingles or run down the fascia, where it would rot the wood over time. It also gives the roof edge a crisp, finished line and supports the overhang of the first shingle course. Many codes now require it on new roofs.
How drip edge is counted
Drip edge is sold in sticks — commonly 10 feet each — and counted by the linear feet of eave plus rake, divided by the stick length. A roof with 80 feet of eave and 60 feet of rake has 140 linear feet of edge, needing 14 sticks. Pieces overlap slightly at joints, so rounding up covers the laps. The calculator derives drip edge from the eave and rake lengths you enter.
Where flashing goes
Flashing seals the joints where the roof plane meets something else — walls, chimneys, skylights, vent pipes, and the valleys where two planes meet. These transitions are the single most common source of roof leaks, far more than the open field of shingles. Step flashing at walls, counter-flashing at chimneys, boots at pipes, and valley flashing each address a specific joint and failure mode.
Why edges and flashing get under-ordered
Because field shingles dominate the order by volume and cost, the edge metal and flashing are easy to overlook on a quick estimate — and a roof short on drip edge or valley flashing cannot be finished correctly. Counting eave, rake, hip, ridge, and valley lengths separately keeps these items on the list rather than discovered missing on install day.
Flashing is the part that rewards a close look
Of everything on a roof, flashing detail depends most on your roof's specific penetrations — how many vents, whether there is a chimney, how the roof meets walls. That makes it the one part of an estimate that benefits from actually looking at the structure rather than a formula. Get the field and edge counts from the calculator, then tally flashing against the actual penetrations on your roof.