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Dallas, Tex. Building a new home. Builder does not insulate garage. We had a friend put in r-13 faced but he installed it paper side against sheathing on outside wall. Is this ok?

  • Hello, and welcome to Home Improvement. Are you heating, cooling, or both? – Daniel Griscom Apr 20 at 17:58
  • Has the drywall been put up? – Jim Stewart Apr 20 at 18:21
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I have seen controversy about vapour barriers, especially in heating climates.

The potential problem is that when it's colder outside than inside the garage water vapour moves thorugh the wall and condenses on the paper. This produces mould inside the wall.

I don't know if this would happen in Dallas's climate. Wall mould tends to be a problem here (Canadian prairie to arctic) in extreme heating environments (high arctic) or houses that have very careful attention to air leakage, but don't have sufficient ventilation. This results in high humidity inside, which then can condense inside the wall. But we have a 10,000 degree day heating season spanning 6 months in Edmonton. Exciting hot spots like Grise Fjord and Cambridge Bay are far colder.

Neither seems likely. Garages generally are not well sealed for air leakage -- it's tough to do this with a tracked garage door. Nor do you have an extreme heating season.

If you get different advice, or want to check:

  • Embed a couple of cheap remote temperature/humidity sensors in the wall right next to the paper.
  • Leave a place where you can remove the inside sheathing and reach in burrow through the insulation and touch or look at the paper.
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As a "primarily cooling climate" (which is how I, from a primarily heating climate, think of Dallas, but I've never been there) that's where you want the vapor barrier - on the side that is, on average for the year, warmer.

In a primarily heating climate, it goes on the inside.

In the pesky in-between zones there are arguments favoring none, and there's also the argument that either side is fine, or that you should look at the likely humidity (on average) as well as the temperature (on average) in making your call. You could also take the approach of looking at what was done on the house insulation...

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