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I live in southern Brazil and I don't really know if I need a vapor barrier, mainly because I'm still confused about its purpose.

The house in question have brick exterior walls and interior drywall. At first I thought that I might need the vapor barrier in the wall between batrooms-bedroom and bathroom-bathroom. But after some research, it seems to be that vapor barrier is meant to avoid condensation on colder climates in heated houses, is that so?

Here we don't have cold winters (around 10-15°C average) and or summers can get quite hot (35°C average).

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Generally useful articles on this: buildingscience.com/resources/vapor_barrier_code_changes – gregmac Apr 29 '13 at 16:15
up vote 6 down vote accepted

Yes vapor barriers are to prevent condensation inside of insulation, greatly reducing its efficiency. In your climate, if you use air conditioning and that space has insulated exterior walls, you will want a vapor barrier on the exterior side of the insulation to prevent outside humidity from condensing inside the cooler insulation. If your exterior walls are just solid masonry, no vapor barrier is required.

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Thanks for clarifying. Also, between wet (shower) and dry (bedroom) areas, do I need anything else inside the drywall for safety? Considering waterproofed greenboard is being used on the wet side. – Luiz Borges Apr 29 '13 at 18:08
Vapor barriers in humid climates also prevent water vapor from the humid outdoor air from entering the living space. If the building is air-conditioned, a vapor barrier will reduce the amount of moisture the AC unit has to remove from the interior air, making it run more efficiently. – Evan Johnson Apr 29 '13 at 21:28
Hi Luiz - No, you do not need vapor barriers on interior walls. Since there is little temperature difference between spaces, condensation risk is minimal. You do however, want to have means of removing excess moisture from the damp spaces, either by operable window or opening and/or exhaust fans. This is more for occupant comfort and reduced AC loads (thx Evan, good point) than for protecting building materials. – bcworkz Apr 30 '13 at 21:39

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