Why is moisture running out of duct work in attic?

Question

I bought house in 1996 that was built in 1954 without any a/c. Since half of house is on a slab we installed a/c duct work in attic in fall 1996. Installed 12 more inches insulation in attic in Jan. 2001. Put new windows in Jan. 2003 and new garage door in May 2003. Old garage door was too heavy for wife to open so we left it open all the time till new door was installed. Had no trouble till I had new windows put in. About a week after installation, I noticed ceiling was changing color and started to inspect. Noticed that the marks were about every 3-4 foot and directly under duct work in attic. Went in attic and found water running out at every joint in duct work. People who installed air came back and wrapped insulation around duct work in mar. 2003. Seemed to help but it still leaks a little. Ran 2 dehumidifiers this winter keeping basement at 20% and upstairs at 30-35%. I have hot water heat so duct work is not used in winter.

Answer 1

basically your ductwork is doing the same thing a cold glass of iced tea does sitting on a table outside in the summertime. Water is condensing on the outside of the duct, because the air moving through the duct is much colder than the air in the attic.
This normally happens in the summertime, when the air conditioning is blowing cold air through the ductwork, and the air in the attic is hot.
So basically, to get this to happen in the winter time, two things have to be wrong at the same time.
1. the insulators have possibly covered up vents in your attic that keep outside air circulating through your attic space. Heat is radiating up through the ceiling into the attic, and is getting trapped up there.
2. cold air is moving through your ductwork. This can happen through convection, or through negative pressurization. check to see if you can feel air being drawn through the return in the house while the fan is off. The easiest way is to hold a piece of paper next to the return and see if it sucks the paper up against the grill. Saran wrap is a cheap way to block off air circulating through your ductwork during the winter.
3. Finally, check to see if the contractor installed a fresh-air intake on your forced air system in the attic, it may also be sucking in cold air. It should be equipped with a damper that you can simply shut during winter months.
The key to all of this is to raise the dew point in the attic, and stabilize the temperature of the air inside the ductwork during winter months. (More insulation is not going to fix this)
Its funny- you have made your house almost "too efficient"