The rake edge is the sloped edge of a roof that runs along a gable end, from the eave up to the ridge, as opposed to the eave, which runs along the horizontal side of the house. Like the eave, the rake edge is finished with drip edge to guide water off cleanly and give the shingles a straight line to overhang. Because wind hits the rake edge at an angle, shingles and drip edge there are especially important for keeping the roof's perimeter sealed against wind-driven rain.
Every sloped roof has two kinds of edges. The eave runs horizontally along the low side of a slope, and the rake edge runs diagonally up the gable end, following the roof from the eave to the ridge.
On a gable roof, the rake edge is the line you see forming the sloped silhouette of the triangular gable end, finished with its own drip edge and trim board.
Drip edge along the rake works the same way it does at the eave, giving water a clean path off the roof instead of letting it curl back under the shingles at the edge, and giving the shingle courses a straight, supported line to overhang.
The rake edge also takes wind differently than the eave. Wind blowing across a gable roof tends to hit the rake at an angle and can get up underneath a loose shingle edge or a lifted section of drip edge.
That is why proper fastening and adhesive along the rake matter as much as anywhere else on the roof, even though the rake sees less standing water than the eave does. A rake edge finished without a trim board or with a warped one also tends to telegraph a wavy shingle line down the whole slope.
A straight, tight rake edge is part of what a clean roofing job looks like from the street. A wavy or gapped rake line, or drip edge that is loose or missing along the gable, is a punch-list item at any inspection or new installation.
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