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?
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.
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.)
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.
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.
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.
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
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
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