How to Trim Shingles in a Roofing Valley

A roofing valley in a roof consists of the point where two inclines (gables) meet. Because these valleys can channel rainwater, incorrectly trimming shingles can result in leaks as rain gets between the cracks, flows under the shingles and collects in your sub-roofing. In the winter, snow and ice can also collect in poorly trimmed areas, and the asphalt underlayment can erode over time. Correctly trimming shingles along roof valleys will provide as solid a barrier as any other portion of your roof.

Metal ruler
Carpenter's razor
White chalk

Instructions

- 1
  Center one shingle lengthwise in the valley.
- 2
  Press the shingle into the valley, causing it to fold along the angle of the roof's valley.
- 3
  Hold the metal ruler across the shingle's crease
- 4
  Cut the shingle along the crease using the carpenter's razor.
- 5
  Mark the left half "L" and the right half "R" using the chalk. These two shingle portions will serve as templates for shingles that you need to trim.
- 6
  Place the cut shingle templates over the top of any shingle requiring trimming.
- 7
  Cut the shingles needing trimming with the carpenter's razor, using the template as a straight edge.

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