"jeffc" wrote in message
...
One year old house. I was in the crawlspace (no basement) and noticed the
subflooring was wet around one of the air vents. The line is pretty well
insulated all the way to the vent. I'm not sure why that vent in
particular would be a problem, but it seems to be the only one. I'm
concerned the subfloor will start to rot over time. I checked it about a
month ago and it was the same. There is no moisture I can detect from
inside the house on the floor (pine flooring.) Any ideas why this is
happening or what to do? I will call the builder, but it's a couple months
beyond warranty and he might not do anything. Need to be armed with
information....


Condensation.

Just as when you sit a glass of ice water on the table for a while, moisture
from the air will condense on the coat surface. It must be insulated and
sealed better. Hard to say what will work best because I can't see what you
have, but a wrap or fiberglass, or a spray of insulating foam will probably
fix the problems. Yes, over years it can be a serious mold or rot problem.

You may also want to look at what you can do to reduce the moisture in the
crawlspace. Plastic over the dirt, ventilation, etc.