Vapor Barrier Location

If the VB is located on the warm side in cold and hot climates,
where do you put the VB in temperate climates?

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Great question @linda! @coachbryanhadley do you mind helping Linda.

Hi, Any feedback on this one?

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@coachdarionziegler do you mind helping @linda with this question?

Hi @linda,

In most cases, what I assume you are considering a temperate climate will have the vapor retarder located on the inside face, as this will be the ‘warm’ face for a significant portion of the year. However, it’s important to note that the building code doesn’t identify “temperate” climates. It identifies the climates below per the IECC:

Placing the vapor retarder on the warm face is the general logic. In practice, it is a little more complex than this. If you’d like to read into it further you can check out Chaper 14 of the IBC chapter 1404.3 “Vapor Retarders”. There are class 1, 2, & 3 vapor retarders that may be used depending on the climate zone and insulation of the wall assembly. You cross reference this section with the IECC (International Energy Conservation Code) to determine what kind of vapor retarder you need.

And lastly, “vapor barrier” is sort of the colloquial word for these. The technically appropriate term is “vapor retarder” although these get used interchangeably often.

This article helps explain it concisely:

Hope this helps!



@coachdarionziegler does this mean that the generic placement of vapor barriers/retarders, they go on the warm side?

Hi @Toshea.Shouse ,

Yes! The rule of thumb for vapor retarder placement is to put them on the warm side of the construction!

Always try to use retarder instead of barrier if you’re talking about the material that goes within the wall assembly – the vapor retarded still has a certain amount of permeability to prevent water from getting stuck in the assembly.

A vapor barrier is meant to prevent all transmission of vapor and has been used colloquially to refer to vapor retarders as well. This website does a better job explaining it than I can:

Hope this helps!