I'll say, it's not ideal but that doesn't mean it won't be just fine if its flashed and finished properly. Fortunately you have a good size eave right above it and because of the roof slopes not much rain will head to that valley. You may get some debris build up but it really just depends on your site and the wind around your house. If you extended the porch roof into the 10/12 roof you would still have a condition that needed to flashed properly to prevent future headaches. The advantage to the location of this valley however is that it appears it is entirely 'outside' so it is not over an interior finished space - and I would much rather have a leaky roof over a porch than a leaky roof over a living room.

Thanks for the input. You're pretty much confirming what I was thinking about everything. I'll just have to keep a close eye on how they flash it when they install the roof.

Let me see if I can reverse engineer this question and have it make sense ;D

Most roof shingles are designed to go on a minimum slope of 4" vertically in 12" horizontal. On a standard roof with a 90 degree intersection, and a 4/12 pitch, the slope straight up the valley is 4" vertical in 16.97" horizontal, or 2.83/12.

IMO, anything less than that will require a roofing system in the valley designed for a flat roof. Standard valley flashing for a shingled roof will not work no matter how elaborate they try to make it look.., even with ice and water shield.

Or add a cricket @ a 4/12 pitch.

Water and ice shield that whole area, including a foot up the wall. You will regret if you don't.

The one solution I see would be to change the porch roof. Raise it and add a frieze underneath it. The frieze would be great enough in vertical height that the garage roof would die into it. The porch posts would need to be be at least 6" taller, which can't hurt as the porch reads as very squat.

Then the two roofs are independent. Would the porch roof pitch need to wind up flatter to miss the windows? I can't tell. A flat soldered metal roof would not be a bad thing. Or EPDM; nobody is really going to see it.

Casey