11:29AM | 07/16/03
Member Since: 07/15/03
1 lifetime posts
I just added a room on the back of my house and I suspect that the copper fhashing is not installed properly because it leaks in that area of the valley during a hard rain. My roof has an 8x12 pitch and is covered with fiberglass shingles.My question is, how far should the flashing extend under the shingles on either side of the valley?


10:57AM | 07/21/03
Member Since: 01/21/03
66 lifetime posts
Your roofer will usually use a 24-inch wide pan folded in the middle. Some use a 36-inch wide sheet metal. However, it is prudent to have at least 36" width of unbroken underlayment under the valley. Your problem could be water shooting from one side of the valley and running up the slope (under the shingles) on the other side. If that's the problem, then you need a W-valley (that's a valley with a ridge running down the middle), which blocks water from crossing the mid-point of the valley. They are not very common, but relatively easy to bend on a portable bender.


07:53PM | 07/27/03
Member Since: 11/06/02
1280 lifetime posts
There is rarely any reason for the metal itself to be any wider than 16" with 8 on each side because the first rule of using metal valleys is that one must not drive nails into the metal. Use wider metal and you cannot fasten down the shingles.

There are at least five ways of running a valley, all having good purposes and places where they are best choice.

My bet is that your leak comes not fromn the size of underlap in the valley but from some error in the way it was installed.

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