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Other than cost for the galvanized or copper valleys on homes today, is there any advantage to using shingles. Very few are even replacing the metal on older homes, and I always question this. I'm sure someone can here can give a unbiased opinion. Thank you.
My guess would be cost is the main factor. Both labor and material would cost more for a metal valley roof. If they eliminate metal, they don't have any cost for metal. Copper in particular is expensive. Plus you don't have to have metal working skills to put down shingles. There is also the fact that you don't have as much shingle trimming to do by weaving the valleys. The advent of Ices and water shield would also reduce the need for metal valley flashing to get a dry roof.
I always recommend shingles over metal. A properly woven valley will last just as long as the rest of the shingles and I find they don't creak like metal.
The only time metal valley makes a good way to go is when the roof is steep, 10/12 or steeper (unless 3-tab shingles are used). The architecture type shingle are rather tough to weave as the pitch increases.
I have to disagree. With a condition. If.....
If you are in heavy trees, especially pines, a metal valley is a better way to go. It is self cleaning. In a shingled valley when pine needles collect they rot the shingles out in a very short period of time.
Bitutane is a bandaid which should not be used as an excuse to do stupid things. People designing roofs are runnng valleys into the side of dormers and all kinds of stupid designs counting on the bitutane to stop the water, and it just does not work. For one saturated shingles rot in a hurry, and two wood moves, so those nails through bitutane do not always stop the water.
As an inexpensive alternative to custom metal work I use pole barn ridge cap upside down for valleys. It is very heavy steel that I could no bend on my brake, has a dropped center section about 6" wide when upside down, and will be self cleaning every time you get a good rain. And it is cheap!
I give the metal a couple of more coats of paint. Then I put bitutane under the metal in the valley as a second line of defence, nail down the metal, split a piece of bitutane and run it out on to the metal, shingle to the break in the metal where the center section is exposed, putting no nails closer than 12" to the valley center. Has not failed me and I have been doing this for about thirty years. If a house is out in the open I will do a basketweave, but in the trees I do it this way.
Larry