What kind of flashing
Usually, when we use Sheet metal valley liners, we get the color coated Pac-Clad or Copper. Regular galvanized will eventually show off its rusting abilities, even though it is not supposed to.
24 " wide metal comprised of either 24 Guage steel or if you choose aluminum instead, then order .040 mm thickness for sturdiness and less chance of puncturing accidentally.
Theree should be an upside down "V" in the center to prevent water flowage and migration under the opposite side of the valley shingles, which becomes more important the steeper the pitch is.
An open valley will not clog up with leaves and pine needles as readily.
The side edges should have a hem bent in them and you are supposed to use sheet metal cleats to hold the metal in place versus nailing through the metal valley to allow for expansion and contraction from thermal schock.
I don't buy into that premise, unless you are doing an entire metal roof. After all, the nails from the shingles are going to penetrate the sheet metal anyways.
If, per chance you go with the copper valley metal, buy one or two pounds of copper roofing 1 1/4" nails to nail the valley shingles in with. Otherwise you will have the corrosion by electrolysis problem discussed previously, for sure.
A slight bit of roofing cement from a caulking tube under each of the end edges of the final valley shingles will assist in preventing water back up under the edges of the shingles.
I believe the code you referenced would allow lee-way, as an either/or situation regarding the ice and water shield versus the sheet metal valley liner. I personally would prefer only the ice and water shield method, especially for someone who does not have any sheet metal experience. You will see what I mean at both the bottom of the valley at the inside corner and at the to edge of the final piece of valley metal.
At that point you will be asking additional questions. Visualize it and you may realize what I am implying.
Last edited by Ed the Roofer; 06-20-2007 at 08:20 PM.