As I understand it, the paper facing is to stop the warm air on the inside of the house from going to the cold air outside of the house, thus preventing condensation.

But what about areas that have swapping temperatures. For example, in the winter the house is warmer than outside, so facing the barriers inwards stops the warm air from going out. But in the summer when it’s the reverse (and especially humid), the paper is facing inward so doesn’t that trap condensation between the siding and the walls? Or is this prevented somehow by the TyVek barriers I always see?

If it is related to the TyVek, isn’t it bad to have a vapor barrier on both sides of a frame? Or does TyVek prevent moister from entering one side but still allows it to dry out from the other like some poly-membranes?

  • does the paper has thermal properties ?
    – Traveler
    Jul 31, 2022 at 3:57
  • @Ruskes Um, no? It's a vapor retarder, like on insulation batts.
    – pstatix
    Jul 31, 2022 at 4:16
  • so the humidity is always higher outside then inside
    – Traveler
    Jul 31, 2022 at 4:26
  • Have you considered using unfaced insulation? Jul 31, 2022 at 5:45
  • @Ruskes in the Spring/Summer in my state, humidity is more outside than inside (we have a great HVAC)
    – pstatix
    Jul 31, 2022 at 15:43

1 Answer 1


Vapor barrier goes on the warm side - as a seasonal average.

If you cool more than you heat, it goes outside. If you heat more than you cool, it goes inside.

Tyvek and other housewraps are very specifically air barriers, not vapor barriers. They prevent bulk air movement and fluid water ingress while permitting vapor to pass through.

Using cellulose insulation (not fiberglass) with no barrier is a good option if your climate puts you in doubt, as it retards air movement and manages moisture. (Manufacturer link, no particular affiliation.)

  • So the direction of the barrier is dependent on which side is warmer on average in a year? So if I cool my house for 4 months but heat if for 8, barriers need to be inward?
    – pstatix
    Jul 31, 2022 at 15:42

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