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Old 03-19-2013, 09:43 AM   #1
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Attic Ventillation Problem. Why Now?

This winter in attic noticed ice on roofing nails. Obviously warm moist air condensed and then froze on cold nails. When weather broke and warmed up a bit, I was back up in attic and noticed black mold on certain areas of lower attic ceiling going toward eves area.
Some interesting facts:
Been in house 2 years and did not notice this happening last year
This is only occurring on one side of attic ceiling, other side is completely fine (no rusted nails poking through, no mold)
Recently put down some more plywood so can have more areas for storage, and before did that added some more insulation to attic floor (rolls). Wonder if that has anything to do with it?
Also was a colder drier winter this year so we had humidifiers in use more, so that may also have something to do with it.
Just curious why it is happening this year and not last year, why on only one side of attic ceiling (roof).
Important Information:
For ventilation of attic we have only two gable vents (one on each side of house), about 1.5ft x 2ft rectangle each. These do not have any fan.
There are no soffit vents or ridge or roof vents; just the 2 gable vents.
Looking at lower part of where attic roof slopes down and meets wall I notice there is a board that blocks attic area from soffit area/eve. So if I was to put in soffit vents from outside, I believe I would have to also drill holes from inside attic through this board so the outside air could actually pass into attic and not be trapped out in this blocked off area.
Attic space is about 600sq ft.
Only insulation is in attic floor and on walls, no insulation on attic ceiling.
Bathroom fans are vented to outside the home (not into attic or soffit)
I live in North East (MA) where winters get cold and summers are hot and humid.
What to do?
Why was the gable venting system in place good enough last year but not this year?
Why only one side of attic affected?
I recently beefed up the insulation and seal on pull down attic entrance as this could be an area where warm moist air was entering into attic (the entrance is on same side as attic problem area). Will that fix problem, or do you recommend installing more ventillation anyways?
Will a van on gables do the trick, or do I need to install soffit vents anyway?
Will soffits with the gables work, or will ridge or roof venting also be required?
Sorry about the long post, but wanted to give you as much info as possible so I can get best feedback. Thank you.


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Old 03-19-2013, 10:07 AM   #2
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Post a picture of the outside of the house.
With no soffit vents a gable vent is all but useless. Plus a gable only vents the ends of the attic and air stays trapped between the rafter bays.
Take a straw and put your finger over the end of it and suck on it, that's what happens with no soffit vents.
Did you air seal any place where plumbing, wiring, ceiling fixtures where run with spray foam?


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Old 03-19-2013, 10:23 AM   #3
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I suspect you were very close to the dew point just below the deck on the side where you are having trouble, and the addition of the humidifier broke the camels back, so to speak. In other words the furnace ran more, and the temperature/ humidity differential increased, so the vapor pressure increased, and caused the current situation.

Putting a powered fan with a humidistat/thermostat in one gable end and drawing outside air through the attic from the other end might solve the problem. Its worth a try before you go into other more extreme measures.
" Most people would rather die than think, and most do " Bertrand Russell

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