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You are here: Experts > Home/Garden > Home Improvement/Repair > Roofing > Leaves in Roof Vent
Roofing - Leaves in Roof Vent
Expert: Brad Zacharia - 11/3/2009
Question
QUESTION: Hi Brad,
After a hard rainstorm last week, I noticed some dampness in the wood near the attic of my oven/range hood vent. This is a typical range vent with a flat back along the top, and it is probably installed with the upper course of shingles laying over the top edge of the vent flashing with a small gap between the end of that shingles and the vent itself (with flashing underneath extending under those shingles).
I went on the roof and noticed that leaves had clogged the gap between the back of the vent (which is on the top side, where the water hits as it comes down) and that upper course of shingles above the vent. I believe that these leaves caused the leak by preventing the water from draining around the vent down the flashing on the sides. Enough water gathered there quickly enough during that hard rain to back up under the upper course of the shingles and work its way back under the flashing. Hence, the leak.
I could clean out the leaves and stop the problem now. But to prevent this problem in the future, I thought I would apply a small bead of caulk to fill in the small gap between the back of the vent and the upper course of shingles. This isn't to prevent water intrusion, but to prevent leaves from filling in that gap. That way, the water running over the upper course of shingles runs directly into the back of the vent (since the caulk prevents it from getting into that gap), and is then directed to the sides of the flashing. That leaves no chance of water backing up under this upper course of shingles again.
I know from your previous postings that you're not a fan of caulking, but in this case, since the flashing is still secure and properly done, I thought this might solve this particular problem. Your thoughts?
ANSWER: Your pipe collar was installed incorrectly. I don't know the details without seeing pictures but your leak did not occur because you got leaves in a seam.
When things are done incorrectly then you need "Plan B" which is caulking. But the caulking will not last nearly as long as the shingles so you'll be up there every few years redoing it and that will get your attention due to a leak and more damage. Do the collar right and NOTHING needs to be done to it for the life of the roof.
Brad
---------- FOLLOW-UP ----------
QUESTION: Brad,
Thanks for your answer. Here's a picture. You are looking from the top to the bottom down the slope of the roof. I looked everywhere for another potential source of the leak, but I didn't see anything. The amount of water was very small--it was basically just a little dampness in the decking right near the top of the flashing of that vent should be, so that's why I thought water was running up under the shingles and under the flashing.
My plan with the caulk was to fill in that gap between the shingles and the vent to keep leaves (and water) from going down into that gap. It would run straight off the shingle into the back of the vent and then move to the sides. Since the caulk would be thick, I figured it would last awhile. And if it failed, there's still flashing underneath.
Do you see anything else that signals an improper installation? Do you think this is a "couldn't hurt" type fix--i.e., one that doesn't hurt to try? I couldn't think of a potential problem that this would cause, since the could basically would be functioning in the same way the shingle would be if it ran all the way into the back of the vent.
Thanks very much for your help.
Answer
It's not a typical hood. Most are round. Two possibilities.
1. The corners of the vent metal are open due to some manufacturing problem.
2. Nails were placed in the wrong location on the flashing (more likely scenario).
Water is supposed to hit the back of the vent and run to the sides and then down. The water needs room. The shingles should not be cut so close to the vertical part of the vent. No nails should be near the edge of the shingles or down the sides of the vent except at the very edge. Many roofers just nail everything without knowing where they can nail. Water does go under the shingles on the side but will come back out the bottom. If the water hits a nail along the way you can get a leak. Without taking this all apart to do it right I guess you'll have to use caulking. It doesn't matter if you do a lot of caulking. The caulking will expand and contract differently than the shingle and eventually they will separate.
Make sure the first shingle behind the vent doesn't have a vertical seam there behind the vent.
I'm assuming that the roof has a good slope to drain water. Many times people do shingles on roof on slopes too low for shingles and then the roof will leak no matter what you do.
The front of the vent is also a common problem due to improper installation but I can't see that from the picture.
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