Valley exit overshoot issues caused by a truncated mini-dormer

I will be re-roofing with comp shingle. The photos show the old roof at a decorative mini-dormer. The mini-valleys lack a decent path for the exit water because the main roof’s eave fascia stop above the mini-dormer’s decorative barge rafters. The photos depict an attempt to move the water into the tapered 3” shop gutters and keep it off the 4x4 outriggers.
Short of extending the mini-dormer cantilever an extra 12”, or removing the dormer and building a continuous eave, can anyone suggest how to best flash / gutter the existing roofline?

My I ask a few questions because I have too come across this and we came up with a nifty solution.

  1. Is ice damming a threat for the location?
  2. Is sustained rain common for the area or is it torrential downpours due to storm cells?
  3. It looks like a 4:12. Is that correct?
  4. How “married” is the homeowner to the scrolled fascia?
  5. Are they willing to put on new gutters as these appear ancient and I suspect water overshoots them everywhere.

I don’t want to speak out of school but I may have a “non-invasive” fix.

In response to Ivoman’s questions:

  1. This is a San Francisco bay area location with no snow or ice

  2. Sustained rain is highly unusual. Sometimes Pacific storm cells drop a few inches over a few days in the rainy season Nov-April

  3. 4:12 is correct

  4. There is no attachment to the gingerbread fascia

  5. New, correctly sized and mounted gutters are indeed desired. Ideally this would be a gutter mounting and counter-flashing system that can be installed independently of the new roof.

Thanks for your response. we encountered an overshoot situation where storm cells would dump a swimming pool of water onto the roof in 20 minutes. We then realized it was a volume of water issue and we had to somehow figure out how to either divert or slow the flow. Metal valleys are low friction highways where water gains a great amount of velocity. With that velocity, it tends to hose off the end of the valley and naturally overshoot the gutters. Another issue being the volume of water fed from the upslope. In this case, there is a great deal of roof feeding these valleys and contributing to the torrent.

Solution: divert the flow away from the valley and interrupt the laminar flow from upslope. This will lessen the burden of water load in these two valleys. As well, close these valleys as the abrasion of the shingles will aid by creating friction when water flows over it. Once the flow has been diverted and controlled, splash guards should manage the overflow on new gutters capable of catching the overshoot.

We had to concern ourselves with ice damming and therefore had to be mindful of trapping ice and snow during the winter months. If that is not an issue for you, simply exaggerate the pattern and make the diversions taller. Move the water away from the valleys with color matched diverters.

It works quite well and is not unlike the technology used in weirs, spillways and highway ditches.

(Please excuse the quality of my illustration)

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Ivoman, I really appreciate your observations and suggestions which expanded my thinking 100%.

Its like “Water Judo”! If you can’t stop the water, push it out of the way using its own force. Good luck and I’m glad to hear it triggered some “possibilities” in your mind.

Water, unobstructed, seeks it’s own level… Water Zen

Ivoman, Greetings. Must these diverters be installed integral to a re-roof job, or can I slip them under the new shingles myself afterwards on a trial basis? (My new comp shingles will be mid-range architectural i.e. not the heaviest kind.)

Run a standard valley detail and you won’t have issues, the metal makes the water move too fast.

Hi Dougster, it may be worth sliding a few under the shingles as a trial. If it doesn’t work out, you may be stuck replacing a few shingles if you want to remove the diverters … no big deal.

Can’t believe you still have a shake roof in the SF Bay area , you’re ins. must be astronimical. You could always put a catch and downspout at the bottom of that valley