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Marc

Asymmetrical roof valley

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A client changed their roof cover based mostly on a long term leak on an asymmetrical roof valley (bottom half is 12/12 on one side, 4/12 on the other. Top half is 12/12 on both sides).  I specified a prefabbed copper flashing at the junction between the upper and lower halves because that point has three dimensions (flat flashing can't be bent to fit).

Two months later, it's leaking again.  Is anyone aware of any guidelines for flashing an asymmetrical valley?

Thanks.

Edited by Marc

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Pictures?

Sounds like water running down the steeper pitch is getting up under the shingles on the low slope, past the flashing.

Consider a W flashing to eliminate that.

W flashing.jpg

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She'd wanted a closed valley so we applied a generous serving of Ice/Water all round with copper at the bend in the valley but to no avail.  Maybe W-flashing just at the bottom where the valley is asymmetrical will do.  Still open to ideas.

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18 hours ago, Marc said:

Is anyone aware of any guidelines for flashing an asymmetrical valley?

Thanks.

If there is such a thing I bet it would be the same as  flashing a symmetrical valley with some common sense consideration of water flow.  It's what's behind the shingles that matters.  From memory of a roofing job I did a many  years ago: After tear-off, apply an ice and water shield at each valley that goes a minimum 12 inches over each plane.  At a violent water intersection which this roof has I would increase the water shield considerably.  Follow with underlayment/tarpaper.  No nails should be driven within 12 inches of the valley when applying shingles.  Roofing cement should be used to keep the shingles down near the valley line. 

If it is leaking it sounds like the whole valley part of the roof will need to be redone.

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7 hours ago, Jim Katen said:

If it has a closed-cut valley, the steeper side should overlap the shallower side. 

On the top half, where the two pitches are the same, the higher roof surface overlaps the lower one.  On the bottom half, the higher pitch overlaps the lower pitch.  That means the lap reverses sides midway up the valley, at the point where it changes direction.

I'll take photos when I meet with the homeowner and contractor.

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He didn't.  Why is that important?  Never heard of it before.

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The 45 at the top of shingle reduces the chance of of runoff from opposing roof from running along top edge of shingle, and past metal flashing. This is most commonly done with an open valley though.

Edited by Leighton Jantz

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That's good to know.  According to Chad's drawing, it's done for closed valleys also.   Roofer is arriving tomorrow to talk then leaving for Mexico for three months, so we'll see if he's going to do something.

Edited by Marc

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Over 40 years ago, the first roof I installed leaked buckets at the closed cut valleys. It fixed it completely when I clipped the tops (like the shingle bundle instructions told me to)

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Turns out that the leak was not at the asymmetrical valley but at some roof/wall flashing on a dormer.  I'm hired to replace all roof/wall flashing on the house.  The house is just over 100 yrs old so this will take some time.  The window trim sits on the roof deck so that has to be removed.

Thanks guys.

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