The roof over the main portion of the house is about 9:12 pitch. Along about 3/4 of its length is a secondary roof, about 6:12, over the deck. In the two years I've had the house I have noticed increasing water raining from the kitchen ceiling and dripping from the window frames in the living room mainly during very windy storm conditions.

In the attic, where the main roof decking extends below the secondary roof, I have found that water trickles down on top of the tar paper and drips off the edge onto the ceiling below, about 20" inside of the wall. The living room has a vaulted ceiling which has enough slope to direct the water out to the wall before soaking through the ceiling drywall, where it finds its way out through the window frames or down into the basement.

While the shingles look good to me, it seems obvious that they did not properly layer the tar paper at the intersection of the two roofs. Further, I suspect the root problem here is the 15 slant-back vents allowing blown-in water.

As a cheap and simple patch, I curled the bottom edges of the tar paper to create little gutters along the whole length of the main roof in the attic and directed a "downspout" channel out to the soffit vent at the far edge of the deck. (I only had half done before the last storm, though. Collected a gallon from that half, and likely would have been two from the other half!)

So, now my questions are... is this a typical problem for slant-back vents? Is there an obviously better alternative? I can't see any obvious flaws in the installation, but I have been thinking up ways to modify these vents to obstruct the wind-blown water but not the venting capacity. Any suggestions?

 

Remove them, patch the holes, shingle over it and install a ridge vent. You'll get continuous venting and at a higher (hotter) level of the attic area with a ridge vent system, and no water leakage if installed properly.

 

Sounds like the problem is on the secondary roof which is ontop of the primary roof. I don't think there is a direct path to the ridge.

 

Well, my nifty gutter patch took care of the immediate need, although it was only needed a couple of times since install. While trying to finish an insulation project in the attic I found the gutter system to be in the way so I am back on the roof to see about the vents again.

As I looked closer at the vents, I noticed the gaps under the flanges where these architectural shingles aren't exactly flat. Since the water problem usually occurs during very windy conditions, I wonder if the rain is simply blowing up under the trailing edge of flange. Manufacturers install instructions say nothing about sealing around the edges of the flange and I have not found any mention of doing so in any forums.

1) Likely that rain is coming up under the flanges rather than through the vent grills?
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2) Helpful, irrelevant or harmful to seal with caulk or tar under the lower edge of the vent flange? How about around the top at the edges of the shingles?

3) I plan to address the secondary issue of overlapping the tar paper in the spring unless simply sealing the vents fails to solve the root issue. I don't know if this image will work, but here is a bird's eye view.
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Wow, 5 roof lines. Must be a booger! You can apply a sealant under the leading edge of the vent with no harm done. No need to seal on the top nor the side edges as the flashing will usually take care of that. Blowing rain can infiltrate that lower edge, but not often, that is why they are usually just sealed and not nailed (nails penetrate it and cause a leak position). If your rain is horizontal enough, it will infiltrate those vents, too, so don't discount that possibility.

 

The wind generally comes from the west, directly left in the overhead view, so when it is strong it would tend to force water right into any gaps between shingles or under vents. My original thought was water coming through the vent louvers, so I had considered making some additional deflectors to place around the vents. May still do that if the sealant doesn't work. Then on to pulling shingles at the intersect line between the main and deck roofs if I can find new ones to match.

What is the trick to getting new shingles properly placed and fastened under existing ones in the middle of the field? These particular ones seem awfully stiff (even back in the summer when they were very warm) to try to bend enough to get nails under.

 

The stiffer they are, the more they will break when you try to remove them. There will be, hopefully, 8 to 10 nails holding each shingle in. One row at the shingle's tab and one row in the tab line of the shingle above it, so you will need a cat's paw to remove the shingles you need removed, PLUS one more row's nails. Then slide the new shingles in, matching them side to side with the other ones and nailing from the bottom to the top. The last row will require the formidable "bending" in order to get the last row of nails in. Not sure how they will cooperate.