I'm about to start hanging drywall in the ceiling of my house. Its your not so typical log home, with a very typical store bought truss-roof system. The attic will be well vented from the soffitts. I'll be using blown-in insulation. I'm getting mixed messages regarding vapor barriers. A young guy I know, who makes his living selling building supplies to contractors, tells me I have to staple a vapor barrier to the trusses before I start hanging drywall. He is very well versed in the latest building techniques......and being in the biz......up to date. An old timer I know, who is long since retired from a career in the building trades, tells me vapor barriers are essentially a waste of time. He tells me a vapor barrier over drywall is not needed by any stretch of the imagination. Who is right?