How to Install a Metal Valley on a Roof

Written by mason howard
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One of the common places where leaks begin on a roof is in the valleys. This is because debris tends to build up in these places, which slows down the flow of water. Therefore it is essential to properly install valley flashing. Metal valley flashing is typically made out of galvanised metal and is easy to work with. Install metal valley flashing before attaching new shingles. If you are replacing metal valley or adding a valley to an existing roof, the shingles around the flashing will have to be temporarily removed.

Skill level:

Things you need

  • Metal valley flashing
  • Felt roofing paper
  • Roofing nails
  • Shingles
  • Roofing cement
  • Caulk gun
  • Tin snips
  • Putty knife
  • Utility knife
  • Hammer
  • Chalk line

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  1. 1

    Line the valley with a row of felt roofing paper. Push the centre of the paper into the valley and cut the top and bottom to conform to the front and top edge of the roof.

  2. 2

    Insert the metal valley flashing so it extends from the peak of the roof to the bottom edge of the roof. Trim the ends to line up with the edges using tin snips. If more than one length of flashing is used, make sure the higher piece overlaps the lower piece for downward runoff. Nail the flashing down with roofing nails along the edges of the flashing only. Place a nail every 12 inches. Keep pushing down on the flashing as you nail to ensure that it is laying flat against the roof.

  3. 3

    Use a putty knife to spread roofing cement along the edges of the flashing. Cover the nails in the flashing with the cement.

  4. 4

    Install shingles from one side of the roof so they continue 12 inches beyond the centre of the valley, onto the other side of the roof. Do this for both sides at the same time working from the bottom up, and weave the overlapping shingles as you go. Overlap weaving shingles for downward runoff. Do not nail into the flashing.

  5. 5

    Snap two chalk lines on the shingles for cutting. Place the lines between the centre of the valley and each edge of the flashing.

  6. 6

    Start at the bottom and begin cutting out the section of shingles at the centre of the valley using a utility knife. Slide a piece a sheet metal between the shingles and the flashing as you cut to keep the knife blade from hitting the flashing.

  7. 7

    Caulk two parallel beads of roofing cement on under the edge of the shingles on both sides to adhere the shingles to the flashing.

  8. 8

    Caulk underneath each overlapping shingle along the edges to adhere it to the shingle beneath.

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