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Posted by jolt on November 21, 2006, 2:37 pm
> Hi,
> Before I begin, I will note that I searched the NGs for this problem
> and found enough answers to get me started. I want to get some more
> input based on my specific problem. I just noticed this issue in Nov;
> I'm in MA and its easily below freezing @ night.
>
> HOUSE INFO: Attic shingle nails are wet and many of them have droplets
> hanging/dripping from them.. House is 1.5 yrs old, colonial. R30 in
> attic, kraft-faced, facing living space. Facing is not tacked to
> joists, insulation is just stuffed in from the top. Ridge and soffit
> vents w/ soffit vent "ducts" (no blockages). I keep the heat fairly
> low in the winter (60*). No ice on nails. No rain in the last few
> days (and no snow yet). Never had icicles on the outside of the house
> last winter and roof seemed to have uniform frost/snow coverage.
>
> I'm pretty sure its a condensation issue. I'm going to look at sealing
> up all openings: whole house fan, bathroom fans/ducting and lighting.
> I do remove the WHF in the winter and cover the opening w/ 2 sheets of
> foam insulation (4-5" thick tot.), but this is probably still leaking
> lots of air and hopefully the major culprit.
>
> QUESTIONS: How significant of a problem is this? I don't have any
> water spots on my drywalled ceiling. I noticed it due to water drops
> on attic-side of the access panel (which is insulated and has a foam
> gasket).
>
> Does this stuffed-in kraft-faced fiberglass normally create a
> sufficient vapor barrier? Or will I still have issues after
> super-insulating the items I mentioned above? I'd rather have taped
> 6mil vapor barrier across all the joists coupled w/ unfaced batts
> (prior to furring strips & drywall). I'm under the impression that VB
> should be continuous and right now its far from it.
>
> Lastly, are there any other things to investigate which may help? I'd
> rather not redo the ceiling or add more insulation. I may want to add
> gable vents due to poor exhaust for the WHF (ridge/soffit doesn't cut
> it...another story). Would add'l vents help this condensation problem
> by naturally venting more attic air?
>
> Big thanks,
> -K
>
The two most common reason for what you describe are water in a crawl space
or a whole house humidifier set too high on the humidistat. I've been in
attics in the winter that you could use a raincoat and umbrella. If the RH
(relative humidity) is very high in the house it will migrate to the attic,
where it will condense on the cold decking of the roof.
Sealing up the attic won't help because the circulation of cooler, dryer
outdoor air will lower the RH of air in the attic and would help with your
problem not make it worse. Cooler air can not hold as much vapor as warmer
air, so cooler air is normally dryer air.
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