How to Apply Flashing to the Outside Corner of a Roof

Written by mona culberson
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How to Apply Flashing to the Outside Corner of a Roof
Metal flashing is critical to preventing roof leaks. (log cabin image by jimcox40 from

One of the main sources of roof leaks is improperly installed metal flashing. The purpose of flashing is to redirect the flow of water off the roof to prevent damage. Roof flashing should be weather proof and low maintenance, and is normally made from rust-resistant metals such as galvanised steel, aluminium or copper. Flashing is installed along the edge of the roof and at the point of intersection of walls and shingles. It is also used at the base of chimneys, vents and skylights. The corner edges of the roof are highly vulnerable to leakage. The flashing must be bent and overlapped around these areas securely to ensure a watertight corner.

Skill level:

Things you need

  • Roofing gloves
  • Tape measure
  • Black marker
  • Hammer
  • Roofing nails
  • Metal snips
  • Metal flashing

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  1. 1

    Measure from the last piece of flashing installed to the corner of the roof. Add 2 inches to this measurement for the lap.

  2. 2

    Mark the new piece of metal flashing with the black marker for the cut line.

  3. 3

    Make two full cuts in the metal flashing with the metal snips. Start at the mark on the top of the flashing. Cut down at a 30-degree angle from this mark. Begin at the same mark and cut down at a 30-degree angle on the opposite side to form a triangle.

  4. 4

    Cut a 1/8-inch slit at the bottom of the face of the metal flashing directly below the original mark at the peak of the triangle.

  5. 5

    Bend the metal flashing around the corner using the slit as the bending point at the corner of the roof.

  6. 6

    Hammer roofing nails every 6 inches along the top and bottom of the metal flashing until you reach the end.

  7. 7

    Lap the next piece of flashing over the corner piece 2 inches and continue.

Tips and warnings

  • Always wear protective gloves to protect your hands from the sharp metal edges.

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