To answer some of the posts:

I have 2 bathroom vents on the second floor. Both are ducted to
exterior (I know because 1 of them was not; I had them fix this last
year when I noticed it). But I will be taping the connections as well
as sealing the fixtures against the ceiling.

The chimney does not run through the attic air space - its all exterior
to the building.

No crawl space; its a poured foundation.

I have forced hot water heating only - no air ducts/no central
air/etc...


Thanks for the suggestions so far! Thankfully none of these additional
things seem to apply to my house. Any thoughts on my vapor barrier
(insulation) question? Should this be happening given the current
state of the attic as I've described?

-K