# Moisture inside attic around Skylight



## ccpyue (Dec 30, 2016)

I have a skylight installed about 3 years ago and never check out how it looks like inside the attic. My attic is quite high. Few days ago, have someone installed a bathroom exhaust fan. So I took chance to get in and found that it is like a big chimney. I also found heavy moisture gathering on the attic ceiling at the lower side of that Chimney, also moisture found inside the plastic sheet that hold the insulation around it. I asked the exhaust fan installer, though he is not an insulation expert, but helpfully to check around, he confirmed that is the condensation rising and soaked the plywood ceiling, but he don't how to fix that. This may be a big problem for me. I wish to know how to eliminate the moisture built up there.  (see photos)

As we can see the chimney is round-up with insulation and plastic sheet. Condensation/water appear inside the plastic sheet too, then rise and soak the ceiling. That is what the fan installer told me. 

I hope some experts can tell me how to fix this problem. Thank you so much.


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## nealtw (Dec 30, 2016)

Are you in an area with snow and have you had snow sitting up there?
If yes you might be getting ice dams.

There should not be poly wrapped around the insulation, it needs to breath. House wrap would work better for that or anything that would hold it in place but allow breathing.
Have you got good venting for the attic, soffet vents and vents at the peak , box vents or ridge vent.


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## Gary (Dec 30, 2016)

The vapor barrier should be on the heated side of the fiberglass insulation, the attic side should not have plastic, that's the ventilation side.


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## Gary (Dec 30, 2016)

Neal beat me to it.


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## beachguy005 (Dec 31, 2016)

I couldn't read the printing on the insulation but given that it's there, it could very well be poly wrapped fiberglass that's not a vapor-retarder.


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## oldognewtrick (Dec 31, 2016)

Having seen many stains on decking like that, I'm more inclined to suspect leaking flashing around the skylight. I would start with the skylight installer or a roofer to water test the exterior with a garden hose and see if they can recreate the leak. But, from my chair it's just a guess.


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## ccpyue (Dec 31, 2016)

Thank you very much for the valuable advice. I will first remove all the plastic wrap, as I can see condensed moisture stay on the inside of the plastic wrap. That is what I can do now. If this won't work, I think I need to ask someone to come to check it out.

Thank you again for all the kind help. Happy New Year.


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## ccpyue (Dec 31, 2016)

By the way, I live in Toronto, Canada. Now we have around 10 cm snow, but temperature is around 2 degree C above zero. What is "Ice Dams"? How they look like and how they form?


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## nealtw (Jan 1, 2017)

ccpyue said:


> By the way, I live in Toronto, Canada. Now we have around 10 cm snow, but temperature is around 2 degree C above zero. What is "Ice Dams"? How they look like and how they form?



Ice dams in most cases are a problem over the outside wall. Heat from that wall will spread up to the underside of the roof sheeting and melt the snow above. In cold weather the water from melted snow only runs down a little ways and gets stopped by snow and then re freezes. This can happen over and over again until the water can back up and run in between the shingles and you have a leak.

The fix for that is is cool air from a lower vent moving the heat up into the attic where is can cool.

In your case, in the skylight, the walls go right to the roof sheeting and there is no way to vent it properly so it is really important that the flashing was done properly around the skylight.


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## joecaption (Jan 2, 2017)

If someone laid a sheet of poly over that insulation, it needs to go.
How is this roof vented?
If there's soffit vents, that insulation never should have been jammed into the outside edge like that.
https://www.google.com/search?q=att...RAhVM4yYKHWt7BrkQsAQIGQ#imgrc=Wyi8c4DGpWHD_M:
How thick is that insulation? In your area it should be about R-50 which is around 12" thick.


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## nealtw (Jan 2, 2017)

joecaption said:


> If someone laid a sheet of poly over that insulation, it needs to go.
> How is this roof vented?
> If there's soffit vents, that insulation never should have been jammed into the outside edge like that.
> https://www.google.com/search?q=att...RAhVM4yYKHWt7BrkQsAQIGQ#imgrc=Wyi8c4DGpWHD_M:
> How thick is that insulation? In your area it should be about R-50 which is around 12" thick.



Joe; that's not the outside edge the picture is out 90*. It's the top of the skylight box.


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