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?

 

Go up in your attic. Look up and see all the moisture. Now look DOWN! how much insulation do you have under your feet? It it's less a foot, add another foot of insulation to it.

 

Believe it or not moisture comes from far away places--like your crawl space! if you have one. I have your same problem and added another layer of insulation and vented my bathroom out of the attic--still have moisture--also thought of a dehumidifier--and this is in winter when most people are adding moisture to their homes! But, my dirt floor crawl space is moist also--the pipes are not insulated--so there are two heater vents open down there--and the crawl is vented to outside. I get condensation on the foundation walls and the piping--due to the warm air hitting cold objects--I hope to fix this soon. I also got mold on some of the insides of my exterior walls--due to moisture--along with condensation on inside of new double pane windows--this was fixed by insulating the walls--they had none!

 

At the bottom of this message is a little house icon with www next to it. Click on it and read topics "Air Boundary" and "Ventilation" It will give the rule with free venting and the causes for moisture in your attic. It will also explain what to look for and how to correct it. A dehumidifier will not resolve your problem. The topic ventilation was written for the world, meaning to say that ventilation is applied differently in different area of the States and the world. If you have a question or need for some clarification, click on ask an expert.

 

The info at Resercon's site is an excellent explanation of why there is condensation and frost in attics. If ventilation issues are not addressed, a person's house could literally rot down around them. The mold/mildew can cause serious health problems.

 

Lots of good answers, however Lefty is right. Now I will explain what is really happening. The nails through your roof boards are no doubt from nailing on your shingles. When the weather gets cold, these nails get cold. Now, warm air rises, and the warm area from your main floor is rising through your ceiling and into your attic, hitting the cold nails, and forming condensation, which drips down. Your gable vents are fine. The warm air also is hitting the bottom of your roof sheeting, making it damp, and damp and warm or cool and warm breeds mold. You have two choices. Insulate your roof, or add more insulation to your attic floor. By insulating the roof, you are keeping the heat off the sheeting and nails, and letting your vents work.