My contractor used a weave valley on my roofing job. His given reason: either
would work, but he's quite experienced with, and more comfortable doing weave
valleys, so that's what he normally does.
No problems; I'm in upstate NY.
I still have the metal alleys installed when the house was built 16
years ago. I recently required maintenance due to the following issues:
(TX south facing)
1. Metal creases occur as the flashing is flexed into the valley,
causing galvanizing to crack. Over time, the crack rusts, then leaks.
2. The boundary where the shingles overlap the metal gradually curl.
Piles of leaves standing in the valley form dams, causing the water to
flow laterally under the shingles.
No exposed metal next time.
Open valleys are ugly, but woven ones are hard on the
shingle. Most shingle manufacturers will allow either,
but you could check with the manuf. of your specific ones.
If the roofers are competent, it's untimately
an esthetic issue. If they're not, they're perfectly
capably of screwing up either one. So unless there's
some over-riding reason not to, I'd let the roofer do
it his way.
My first roof had shingles with metal valleys. When the roof was
replaced, it was seen that the cement had hardened and cracked in a
few places, allowing water seapage onto the plywood. Eight plywood
sheets had rotted and had to be replaced. Had I waited until a
hurricane I probably would have discovered major leaks I knew nothing
about. This method seemed to be fairly common. The second roof was
supposed to be better, metal flashing in valleys with the shingles
covering the flashing. Shingles from one side crossed the flashing and
valley and then shingles from the other side covered the shingles from
the first side to the valley. Last year we had two hurricanes and I
discovered major leaks. Fortunately, insurance called for a new roof,
and when the shingles were stripped I had 14 sheets of plywood
replaced this time. As before, every leak was in a valley. The roofer
I used this time called the practise used on the second roof as a
"California Cut" and said weaving was far superior in removing the
possibility of valley leakage. After seeing my first two roofs, I
believe it, and will insist on a woven roof should I ever need another
sometime. It does seem more logical to me that a seamless woven roof
over flashing is better than a joint over flashing. I do live in an
area that gets 70 inches of rain on average with 5 inch days common
plus the occasional hurricane 10 or 15 inch day, and the valleys
become like streams regularly. Perhaps in other areas it doesn't
matter as much, but here valleys have been the weak point and woven
roofs are showing up on more and more houses in this county, and metal
valleys have completely disappeared.
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