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deeptroller t1_iybe6yq wrote

If you have ac on the inside and are managing humidity inside with air conditioning you should have a vapor barrier on the external wall surface. Directly under the siding.

High himidity outside. Cold inner surface creates a risk of condensation near the drywall surface.

In a heating climate you generally want the opposite. Vapor barrier on the inside surface directly under your drywall. Because the inside has the high humidity and the risk of condensation is highest near there outside cold surface.

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Fishy1911 t1_iybgh5q wrote

Warm side of the insulation is what the ABAA typically says.

That being said, we do a lot of vapor permeable on exterior sheathing prior to facade installation in colder climates. It really depends on where your dew point lands in your wall assembly. Which is way above my pay grade.

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dirtd0g t1_iybj0kl wrote

So... What do we do in wildly temperate climates?

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jewishforthejokes t1_iybnx1s wrote

And... that's why vapor barriers are bad. Air barriers are good. Vapor retarders are good. Use both. Don't use vapor barriers.

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Obvious_Equivalent_6 t1_iyby2t8 wrote

This is the correct answer. I wish I could upvote it to the top for reference. Thanks for the link - very helpful. Dr Lstiburek knows his stuff.

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osoALoso t1_iycsct6 wrote

That was a great article, but am I missing something? He gave various examples of proper vapor retarded and layers, but left out the SINGLE MOST common building type in the US. Stick framed houses with OSB sheeting. All. Of his examples were concrete, brick and concrete, brick and block etc.

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jewishforthejokes t1_iydulch wrote

"Frame wall" is wood or steel, both figure 5 and 6 mention sheathing of "non paper-faced exterior gypsum sheathing, plywood, or oriented strand board (OSB)" as do several others.

The article is written using a bit more academic jargon than colloquial terms and is extremely information-dense, so it's not as beginner-friendly as it could be.

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osoALoso t1_iye2dy3 wrote

Maybe I didn't look it over close enough but every outside layer was stone or some stone mixture. Vinyl siding is incredibly common and I'm struggling to understand why house wrap, with rigid foam and osb outside should go with no insulation on the interior.

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jewishforthejokes t1_iyemfyw wrote

Figure 8 but with vinyl siding is fine, which has insulation in the cavity. Vinyl is far more forgiving of a siding material than stone, brick, or stucco so I presume the author didn't find it worth mentioning. Vinyl has lots of gaps so air and water vapor travel freely and it mounts with just nails so there's no brackets causing thermal breaks, so there's almost no way installing vinyl siding can compromise liquid water and vapor management. OTOH it's trivial to install synthetic stucco and trap water somewhere, causing rot and building destruction.

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