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Noticed a water spot on my unused bathroom ceiling.

ceiling

Crawled into the attic And found this is right below the sewer vent.

attic

In my kitchen there is another similar stain right around another drain pipe vent but I haven't Crawled into that side of the attic yet.

We have had some decent rain recently bit it seems odd that both wold start leak g at the same time if it's a roof problem so my gut says condensation.

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    If the water puddle in the drywall ceiling is directly under the roof vent, just like it appears in your photo, it is really hard to believe it is not a leak. – Michael Karas Jun 13 '15 at 16:30
  • Would it make sense to haul a hose onto the roof to test? Or would that cause other problems? – kinar Jun 13 '15 at 16:32
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    You could - but be aware that a short duration blast from a garden hose does not act like wind driven rain nor does it act like casual slow rain that keeps surfaces wet for many hours. So it could still be a leak that you might not see with a few minutes blast from hose. Leaks can occur when wind drives rain up under flashing or shingles. They can also occur because wet surfaces can cause water to flow via wicking or capillary action – Michael Karas Jun 13 '15 at 16:43
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    Next time it rains, crawl up in the attic and take a look at that place. – iLikeDirt Jun 13 '15 at 17:42
  • @ilikedirt I will do that. It supposed to rain tomorrow. Hopefully my fix resolves the problem. – kinar Jun 13 '15 at 21:11
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I went up onto the roof and looked at the vents. The rubber around the pipe was cracked with large gaps on both. unsealed

I added outdoor rated caulking to reseal them.

sealed

Edit - We had a good rain yesterday (3in + with periods of heavy downpour as well as gentle soaking). I had placed some plastic sheeting under the vent in the attic above the bathroom. The bathroom leak did have some leaking still.

The kitchen leak did not register any additional moisture using a moisture meter (I still haven't climbed into that side of the attic) and the moisture (~5%) matched the surrounding ceiling. When I climbed back on the roof, I noticed that the caulk job I did missed some cracks on the bathroom vent (not sure if it bubbled due to air escaping from the attic or if I just missed it).

The kitchen had no such spots. I re-sealed the bathroom and will wait for more rain (tomorrow according to the forecast).

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A third possible (but unlikely) source of the water in your attic:

There's no cap on the roof vent in your picture. So any rain that hits the open end will run down inside the vent line to the drain. In the process it could collect in any horizontal runs that aren't sloped correctly. Add sloppy glue on joints "that only carry gases" and you've got a time bomb.

  • Based on a naked eye test, it appears that the pipe in the picture is sloped correctly but it is certainly a possibility (and probably more likely than condensation). If my attempts to seal the leak in my above answer fails, I will look more closely at this. – kinar Jun 16 '15 at 14:46

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