Thread: Closed (Cut) Valley Installation

Comments on this valley, especially on the lower course installed at right angles to the upper on the left hand field? I get the "logic" in terms of water running down the roof plane into the valley, but it would seem to me that runoff down the valley will run right under those shingles.

The overlap is from higher to lower pitch roof, and there was no way to determine how the valley was flashed or otherwise protected under the shingles.

5 year old roof, no evidence of problems below.

Is this an accepted. documented, alternative to a standard cut valley?

If not, suggestions on recommendations.

Thanks!

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Michael,

Was the roof you were standing on higher? If so, that side (the higher side) should have the overlap).

If not, if both are the same or the one you are on is lower, that is installation is okay.

The reason it works is that water is running vertically down the slope of the roofs, both roof slopes.

Let's first presume both roof slopes are the same height. The water meets in the center of the and neither water flow crosses the center line of the valley as the same amount of water meets with the same amount of force and speed. That water now runs down the center of the valley, and the cut line is pulled back 2" from the center line, so no water is running down the valley trying to get under those shingles.

In theory.

But we all know that water will try to get under those shingles when there is any deviation from theory, such as when more rain is hitting one roof face in greater volume than the other roof face. Thus those are also supposed to be sealed down.

Now presume the roof face to the left is higher than the roof face you are standing on, that roof face will have even more water on it, causing the meeting point to move across the center line of the valley by the difference in the amount of water and force behind it between the two roof faces. This pushes the water even slightly further from the cut back line.

Originally Posted by Michael Thomas

Is this an accepted. documented, alternative to a standard cut valley?

Yes, open valleys are an alternative.

There are open valley with flat roll valley metal and there are open valleys with preformed valley metal with two diverters spaced out from the center of the valley metal.

There are also closed valley with preformed valley metal with one diverter down the center of the valley metal.

The preformed valley metal has returned "slater's edges" which are not intended to be flattened out but left upright and angled toward the center of the valley. Those edges help contain the water into the valley and drain down the center of the valley.

Most people and architects like the looks of the cut back (cut line) valley better than the preformed valley metal valleys.

Check out the details begining around page7 from this shingle manufacturer.

Jerry,

What I'm concerned about is that final course of shingles instated at an angle to the course above and at a right angle to the valley.

I've never seen it done that way before, it appears to me that it aggravates (for example) the problem we attempt to avoid by clipping the corners of shingles on a conventional cut valley, and I was wondering if there is any documentation for approval of this install as opposed to what I usually see...

Jim,

That's a standard closed-cut valley- what I usually see around here - I sometimes use Fig 6-17 in my reports, usually to illustrate the correct use of WSU at this type of valley.

However that's not what I'm seeing here - see the last picture I posted - and I'm wondering if any shingle manufacturer approves that last course installed at an angle.

Look at the one they call "Alternate" closed valley. I think if you will look closely, you will find what is commonly called a "California" closed valley (fig. 6-18) which was described by the instructor at a recent GAF roofing class as the lazy way to make a cut valley since no cutting is required. His take was that this was an acceptable installation for standard shingles for our area.

That's for the guy's who just can't seem to cut a straight valley. Looks funny but works.

Jim,

Yup, that's it... exactly what I needed.

Many thanks!