Attic nails dripping

I live in western NY and the weather here for the last week or so has been around low 30"s, I was in the attic the other day and the nails coming through the roof are dripping water....I have a full ridge vent, full soffit on the west side of the house(and they aren't blocked by any insulation), and gable vents. It is definately cold in the attic and there is about R25 on floor w/ barrier down towards living space, the roof was replaced about 10 yrs ago....what is causing this and should I be concerned?
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Gntry wrote:

Might not be your cause, but I had a similar situation that defied explanation. It was so bad that at times it was practically raining in the attic!
Turns out that that the gas furnace was the culprit. It vented into a brick chimney which had a proper clay flue liner. The chimney was in the center of the attic space.
The original monster furnace had been replaced with a much smaller unit and, I surmise, flue gas temps inside the chimney were now low enough to cause more condensation. This moisture could actually be seen weeping out of the brick mortar joints.
A metallic liner for the flue cured the problem.
Jim
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First, find out whether this is moisture traveling along the nails from the roof top surface to the under side, or condensing from the interior attic air onto the surface of the nails (cooled by their heads through the sheathing.)
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Just guessing but.... I suspect the cause is why a cold glass of beer sweats on a hot summer day. The nail is much colder than the warmer attic air. When dewpoint gets close to temperature you get visible water vapor. Try a small fan to get the air moving. Again, only a guess.

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Haven't experience that, but guessing it may be simple condensation. The nail conducts the cold from the base of the shingles, and if you have a warmish, humid attic, it will condense, just like on the inside of a single glazed window on a cold day. Perhaps your attic needs more ventilation to lower the humidity.

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Roger that, Roger, on the moisture condensing. Under prev. owner, my house had a variety of air leaks from heated space into attic. Roofing nails, having their large heads very near the Great Outdoors and having much greater thermal conductivity than plywood deck, served as main points of condensation. Such that you could see pattern of staining around their protruding shanks in summer. Slowly fading now. And ... energy consumption waaaaay down.
OP might look for entry point(s) of relatively high absolute humidity air from below. They sure are there, and with chimney-effect it doesn't take a lot of flow-area.
HTH, J
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might be condensation. the nails would be at somewhat lower temp than the surrounding materials. is attic vented? any exhaust from the living space vented into the attic instead of outdoors?
bill

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bill allemann wrote:

I think he covered that!

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Maybe a bathroom fan whose duct is leaking moist air into the attic?
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Gntry wrote:

up there. It could be pretty cold and still be warm enough for the nails to be a lot colder. Everything's relative when you're talking about relative humidity. :-)
In fact, you could probably also directly measure the humidity up there with a cheap hygrometer (although I don't know how good they are at cold temps).
Is your furnace in the attic, by any chance?
Could there be gaps in that moisture barrier, perhaps around light fixtures, vent pipes, etc., that are leaking enough conditioned air to carry the moisture you're seeing?
Can you discern whether some are dripping more than others? The worst offenders might be nearest the source of moisture.
I would be concerned, particularly because of the possibility of mold developing.
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Is it possible that the problem is caused by having the attic door opened? If you go up, is the moisture there when you first get there, or only after its been opened for awhile?
Bob
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