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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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thebluelunarmonkey t1_iybybk2 wrote

I'm in GA, no, not in our climate zone it is not required.
If you have housewrap under your siding, you already have a Class III vapor retarder installed in the optimum location - outside of the exterior wall.

The correct term is vapor retarder, a vapor barrier is specifically a Class I vapor retarder which blocks nearly all water vapor. You should ignore all posts which mention 'vapor barrier' instead of 'vapor retarder'. There are only a couple of posts which correctly use the term 'retarder'

In AL you can use rockwool, unfaced fiberglass, or kraft faced fiberglass with kraft paper facing exterior.

Adding a vapor retarder is not a fix for leaking/torn/improperly installed homewrap.

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RedBeard972 OP t1_iyd3qzh wrote

Okay, I have a brick exterior, but when we added an exterior door, there was house wrap on the sheathing.

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krankito701 t1_iybdjz0 wrote

It's a good idea to use vapor barriers regardless, to prevent moisture from damaging interior wall. Unless this is a indoor partition wall

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Verneke t1_iybty3u wrote

Depends a lot on the structure/materials of your wall and you're also on the right track by noting location, proper vapor control depends on balancing the climate inside your home versus the conditions outside which obviously varies place to place (part of the reason its so hard to find one answer!). Links below are of the some of best references that I have found, hope it helps.

General rule of thumb "In areas where the climate is cold in the winter, the vapor retarder should be installed on the inner side of the wall near the warm interior space — or on the warm side in winter. In humid climates or areas where there is extensive use of air-conditioning, if a vapor retarder is required, it should be installed on the exterior side of the wall."

https://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers
https://insulationinstitute.org/im-a-building-or-facility-professional/commercial/installation-guidance/managing-moisture-in-commercial-construction/vapor-retarders/

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Coolguy400 t1_iycn7oa wrote

I had similar situation and ended up using CertainTeed Membrain.

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aereventia t1_iyc08fa wrote

Same vapor retarder for either insulation. Outside the framing. Typically outside the sheathing.

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1feralengineer t1_iybdiny wrote

Generally this is going to be project dependent, but just ask your local building department that is going to inspect your work

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SawdustMaker1 t1_iybfnje wrote

I'm in Canada, not Alabama, but I would say that yes, you should use a vapour barrier. A properly sealed vapour barrier will prevent drafts from getting into the house. Remember to install it on the warm side of the wall to prevent condensation inside the wall cavity.

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killaho69 t1_iybxbat wrote

They mentioned Alabama. Our summers are HOT. Our winters are mild but do sometimes get down low for a week or two at a time. Especially in the northern Alabama which is a little cooler and more prone to snow than central (where I am). So I guess it would be fair to say it’ll be hot or warm most often, but potential to totally flip

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skippingstone t1_iyc3gqx wrote

Just air seal your drywall really well.

Use a gasket before installing the drywall. Or just caulk the bottom.

And air seal outlet boxes really well.

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AsleepNinja t1_iyc86xd wrote

If you can't get a decent answer, then:

  • What happens if you have a vapor barrier and don't need it?
  • What happens if you don't have a vapour barrier and do need it?
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NCSeb t1_iycw3n4 wrote

Did you get a permit for the job? If so, I've found asking the county inspector about things like that was my most valuable resource.

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RedBeard972 OP t1_iyd3jg5 wrote

I’m in the process of getting it. Reason I’m asking is they require I have estimates/bids for every aspect before even allowing the framing to start.

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