Gas and Oil Home Heating Furnaces - attic moisture (frost) and mold

BACKGROUND: My house is less than a year old and the attic has moisture (frost on plywood)and mold growth. Additionally, the nails coming thru the roof when warm outside has water dripping from them. I have been working witht he builder but they are stumped. We have added gable vents on the house and the air flow has increased significantly, but, the frost build up has continued.


QUESTION(S): Is the moisture left over from inadequate ventilation prior to gable vents?

Is there another source of moisture affecting the attic?

How can I rid the attic of the mositure, would placing a dehumidifier work?

Do you have ventilation fans in the ceiling of your bath roooms? If so, are you sure they are vented through the roof, and not just into the attic? Have you checked the vent lines to make sure they have not disconnected or been torn?

Dehumidifier will work, but it is treating the symptom (moisture in the attic), not the disease. The disease is "where is the water coming from to begin with"? That is the question that you need answered.

1) I presume that the "water dripping from the nails when warm" is melted frost in the winter. (not summertime)

2) In addition to bath fan vent ducting, check the clothes drier venting and kitchen stove venting. All must NOT allow venting air and moisture to escape into the attic space. These ducts must be sealed and intact.

3) The ceiling (and walls) should have a vapor barrier to prevent this. The details of sealing these barriers take time and the sometimes the barrier is ineffective because of significant holes, gaps and unsealed joints. (Your walls may be in trouble also.)

4) If you are humidifying the home for comfort, this added humidity can be finding its way into the attic. See 2)and 3)above. If so stop adding humidity as a test.

I too have the same situation. Though my home is 12 years old. Pitched roof with Shingles. I recently bought the home this past summer. I've done some research, and yes, I have all the same symptoms.... frost on the rafters, frozen rusty roof nails, etc... THEORY: As the warmth of your home hits the cold of your attic - moisture/condensation occurs.
So here you go as I share my findings and some questions:

1. Attic Moisture can come from just about anywhere, and some of the others who responded have noted them, ie... Bathroom exhaust fans not vented outside, recessed lights not sealed, etc.... Question to you... The insulating in your attic.... Is it blown-in type or rolled insulation??? I have blown-in insulation. Good stuff, but I don't have a Vapor Barrier. Quick fix is to place some rolled insulation down first, then I can have the blown-in over top. What the Kraft-Faced Insulation(Vapor Barrier) creates is a lockout to a certain extent of moisture to your attic. Keeps the warmth in your home instead of losing it through your attic.

2. They also sell Vapor Barrier paint that you can use on your 2nd. floor ceiling. I'm told also works well.

I've also noticed that the North section of my roof that doesn't get much sunlight is damp. South side is dry.

Please advise more in detail of your situation, ie.... blown-in insulation, what area the sun hits roof????

(PS) A de-humidifier up in the attic will not work in the winter, they typically need to be in warmer temp.'s to operate correctly to draw in the moisture.