DIY Roof "Valley" Repair Question

I'm a DIY roof fixer on a 50-year-old ranch-style house in upstate New York. The roof is in pretty good shape, but some of the tricky parts of the roof (chimney and a major valley) are not done according to the DIY books. The chimney is holding up if I keep the leaves from building up, but the valley is leaking (again). I fixed it for a few years last time with some careful tarring, but I read up enough to know that the valley should have a flashing under the tiles that is two-feet-wide, a foot up each side under the tiles. There is no such thing. As best as I can determine, the original roofer brought the two slopes together and put down a tar and tape 4-inch valley. I don't want to rip up enough tiles to do this right, at least until I am looking at reroofing in general, so what is next-best? 1) just keep tarring holes 2) run a tarring-tape down the valley and tar over it 3) a 4-inch metal flashing, tarred down 4) duct tape, tarred over 5) flashing tape, tarred at the edges 6) something else?
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On Sun, 25 Nov 2007 19:08:34 +0000, Bert Byfield wrote:

It almost seems as though the flashing was installed incorrectly.
Or it could lack ice dam protection thus causing water to seep beneath shingles and then into roof sheathing.
Best would be to carefully remove shingles along valley, redo valley correctly and then reshingle.
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If the pitches that form the valley are equal and the courses line up fairly well, you might consider roofing through the valley. It will mean tearing out a full shingle on each side of the valley, but may give the best long term result. This method is sometimes called lacing or weaving.
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I used the weaving method when I shingled our house. We have a 6/12 pitch on one side, and a 9/12 pitch on the other. It takes a little patience and thinking to keep things looking balanced, but the weaving worked fine even with the uneven roof pitches. I ran a 36" roll of an ice and water protection membrane down the valley before shingling, and kept all nails at least 8 inches away from the valley when nailing the shingles. When necessary, I'd use a shorter section of shingles further back on the roof so I could have a full shingle overlap across the valley. No leaks in over 4 years.
Anthony
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