All attics — vented or unvented — should have an air barrier (a properly detailed airtight drywall ceiling, for example) regardless of climate. Omitting a ceiling vapor barrier by arguing that “you have to let the moisture escape” or “because the house has to breathe out the top” is actually correct, in a way.Click to see full answer. Subsequently, one may also ask, should I put a vapor barrier on my ceiling?If you live in an area with sustained freezing temperatures, you should have a plastic vapor barrier between the drywall and the studs, wherever “warm meets cold” (exterior walls, top floor ceiling).Likewise, do you Vapour barrier ceiling or walls first? The solution is a moisture barrier, called a vapor barrier, covering your exterior walls and ceiling. In most cases, insulation is first installed then covered with the barrier of choice. Additionally, are vapor barriers necessary? In many colder North American climates, vapour barriers are a required part of building construction. You may find that vapour barriers are often not required in warmer climates. And, if installed in the wrong climate or on the wrong side of building materials, a vapour barrier can cause more harm than good.What happens if you don’t use vapor barrier?If water vapor diffuses or infiltrates into the wall cavity and finds the cool surface, moisture problems can occur. Of course, you can have moisure problems here even without the exterior vapor barrier because of what Bill Rose calls the rule of material wetting.