Roof Leaks Downslope of Penetrations

[BS]

This is not exactly a remodeling question but the problem is the result of some home improvement.

Eight years ago I replaced my 20-year old roof, stripping everything off the roof sheathing, placing felt, and installing three-tab fiberglass shingles. A couple years later I added a couple bathroom fans and vented them individually through the roof, one on each side of the plumbing vent pipe (2' spacing). Last year, in heavy rain, water leaked into the attic 1 to 2' downslope of the plumbing vent pipe and one of the attic fan vents. I added more roofing cement around the roof penetrations and that seemed to solve the problem -- or so I thought. A couple months ago we had more heavy rain and the leaks returned, and I added more roofing cement. But the leaks continue in heavy rain.

Since the leaks are directly downslope of the roof penetrations, I suspect water is getting under the felt at one or more penetrations and flowing downslope until it finds an entry route through the sheathing. But I can't figure out how that could be happening.

As far as I can tell the shingles are in good shape and I can see no damage. The only thing that appears unusual is that a couple fo the shingles that overlap the sides of the vent pipe flashing don't lie flat on the flashing but stick up a little. I filled these gaps with roofing cement but it made no difference.

Any suggestions?

- Bernie

 

[PEW]

Bernie,

You are most likely on the right track. Any way to give is a photo from the outside?

Have you noticed the leaks to be any different depending on the direction and strength of the wind / rain?

 

[Sponsor]

 

[BS]

Thanks for your interest, PEW. I'll post photos in the next day or two. I don't recall there being any wind to speak of when it leaked, just heavy rain (as in downpour).

- Bernie

 

[Pewterpower]

Where do you see the leak at? Do you see it from the attic? Or do you just see wet spots on the ceiling?

 

[BS]

The first sign was a wet spot on the ceiling. Up in the attic I saw the water dripping off the sheathing. In April, after my second attempt to stop the leak by applying more roofing cement, I went back into the attic when it started raining. As long as it was a light to moderate rain, there was no leak. But minutes after the downpour started, water began dripping at the joint between two sheets of sheathing and through one or two old nail holes. The leak slowed soon after the downpour turned back to moderate rain. (While I was observing this I was rigging a catchment system of plastic garbage bags.)

- Bernie

 

[Pewterpower]

I went thru something similar recently. Where the water was making its entry thru the ply, was nowhere near where the eventual leak was found.
I put my son in the attic with a cell phone, and I got on the roof with a garden hose, and a cell phone.
I started at the lowest point of the roof, and I soaked it with the hose. I walked upwards a couple more rows of shingles and soaked it some more.
Finally my son said, "We got a leak!"
It was about 4 ft away from where the water was entering the house. When I pulled up some shingles, I found a razor cut in the tar paper that was about 3 ft long. The water was coming in thru a torn shingle, traveling down until it found that razor cut, and then traveling further down until it found a seam in the plywood, and then coming into the house.

 

[BS]

Photos

Finally, here are the photos. Thanks for your patience. I got sidetracked the past few days by another leak, only this one involved copper pipe, a shower valve, and drywall.

I suspect the source of the roof leak is the vent pipe penetration. The water enters the attic through the pylwood sheathing about a foot or so downslope of the vent pipe and the bathroom fan vent to the left of the pipe.

These photos were taken in April just before I applied more roofing cement around all the penetrations.

- Bernie

 

[Leejosepho]

I got on the roof with a garden hose ...

Maybe you could try something like that and look closely at the actual flow of water around the vents. During a heavy rain, maybe there is a "current" of some type that is causing an irregular (such as lateral) flow going under a shingle and out past the vent's skirt/flange.