Thanks for the reply Al.

The vapor barrier is facing the second floor ceiling so that is ok.

The symptons are the nails do have fost on them when it's gets really
cold and there is some frost on the plywood sheating. The north side of
the roof does have some mositure right by the soffet vents (the
affected mositure area is a goes up 2 - 3 feet into the attic).

I had the furance checked out and everything is in working order. One
thing that I did this summer was to seal the area around the base of
the steel stack for the chimney. It did have a mesh area around it that
was used for venting but rain was leaking into the attic. The stack
does have another vent further up the stack but it is much smaller. Do
you think this could be causing the problem?

thanks,
paul