My home has a valley where a roof joint another roof and it is a V
shape, I believe it is called a hog valley.
From the center of the valley there are no roof tiles for about 1 foot
in both directions.
The problem is that this area holds standing water and I'm having
trouble with some water leaking into the attic and studs in one
particular spot. I had a roofer came and he had coated it with what
looks like some tar and then a silver aluminum colored paint/coating.
It's been raining and that spot is wet again. I think the roof guy
will warranty his work but I might have to find a way to fix it myself
because I'm in CA and it doesn't rain very often. My roof is about 8
years old and it's got a layer of old roof below it already. It could
be leaking down from some other spot but I would think it's likely the
Any advice is appreciated.
Yes. You have a tough one. That's because you have two layers. But your
"outer" roof is still young.
The leak is higher than your roofer suspected; I know that because he didn't
fix the problem. Maybe you didn't tell him that you have two roofs.
The wet spot you see is a consequence of the OLD leak in the UNDERLYING
roof. IOW, the new roof is leaking at a higher eleveation, and the water
runs between the layers, only to percolate through the aforementioned old
Why do roofs leak? Sometimes because heavy feet damage the membrane. So
suspect the pathway commonly, and casually, used on the roof. But on a roof
so new as yours, look for outright tears and cracks. And don't forget to
inspect flashing and the caulk that may be required. Is there a chimney in
the mix, here?
If you want to fix a leak, you must "think like water."
And look beyond "hog valley." The water is running to the valley, after
entering in a place you least suspect.
Thanks for the advice, I'm going to fill the valley up when it's dry
to make sure it is NOT the valley's fault first.
However we are going to have rain this whole week.. how can I minimize
the amount of water getting into the house? Perhaps a big tarp?
Yeah, you can do that. But you have to tarp from the bottom to the top; the
entire watershed. Layer it, and fasten it somehow to preclude wind damage.
If your house has no parapet with drain holes (like a commercial building)
then there is less threat of catastrophic roof collapse, in the event that a
tarp manages to obstruct drainage holes. I have not seen a picture of your
roof, so you'll have to evaluate any such threat yourself.
Painter's tarp, as comes in a big roll, either 9' or 12' wide, is one way to
go. Sunlight will disintegrate the plastic if you leave it up there for
three months or so.
Hi John B,
The roofer came back to check out the situation, I shown him the
valley coating did not fix that previous leak.
He looked and measured for a while, and found that the flashing isn't
dropping down to the scrupper, he explained to me there were 2
flashings for the valley. The top flashing seem to be leaking down to
the bottom flashing at the edge, the bottom flashing is about 10 ft
long each and soldered in the middle (and eventually leaks), which is
about where it is leaking inside the house.
He hammered the lip down and applied some flashing cement with a layer
of fiberglass tape and that should make sure the water doesn't leak
into the bottom flashing.
I hope that will fix the problem..
Wait until everything dries, and ppour a bucket of water
into the valley. If it ends up inside, then that's where the leak is.
Drill a 4" hole in the lowest part of that valley, and install
an internal drainpipe. This is why only people with more
"artistic" sense than common sense build roofs that way.
Well, if you're gonna troubleshoot a leak, and you have enough patience,
then you apply water to the lowest suspected elevation, and check for leaks.
You progress higher and higher, until you score. Of course, you might have
leaks in two places, etc.
A flat or hog valley is usually avoided by builders, as they are nearly
impossible to waterproof due to lack of proper slope. Here is a link to what
you may have on your house; http://www.roof.cc/html/photos_problems_0.html
One of the posters above suspect the leak may be above the valley, but
whenever I have had leakage, I found a flat valley to be the cause, even
though the area looked well sealed. As others have suggested, pour from a
bucket or better yet or run water from an open (no nozzle) hose, to see if
leak is really where you suspect. If it doesnt leak, dam up the valley so
it backs up a little, simulating heavy rain. If the leak is there, then I
would be seriously tempted to re-pitch the valley, or rebuild the decking in
that area so there is rapid drainage. I know this isn't what you want to
hear, but valley leaks, if you have one, are damn hard to cure with sealant,
tar or other roof repair goop.
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