Vapor article: Moving from interior to exterior

by Erik Missio | June 2, 2015 12:52 pm

In the May 2015 issue of The Construction Specifier, we published Ted Winslow’s article, “Using Vapor Retarders to Manage Airflow and Reduce Moisture[1].”

On page 81 of the print edition of the magazine, in the second paragraph under the subheading “Climate’s role in specifying air barriers,” the text reads:

In heat-dominated climates, the vapor retarder should be placed at the building envelope’s interior.

This last word should have been “exterior,” Winslow writes:

It should read “exterior” as opposed to “interior.” The language there is a bit misleading as it is very close to “heating-dominated climates,” which would actually be cold climates. A heat-dominated climate would be one subject to large quantities of air-conditioning such as Texas and Arizona.

The reasoning for having a vapor retarder located on the exterior side of the wall in these regions is because the vapor drive is actually in reverse of what one would find in a cold climate like Colorado. Heat moves from hot to cold, and from moist to dry; it condenses on the first cool surface it comes in contact with. This is because the moisture drops out as cooler air cannot hold as much moisture.

If the vapor retarder was on the interior side of the wall in warm climates, then it would condense within the wall assembly and would not be able to dry out as easily since the moisture is driving from the hot and moist exterior to the cooler and dryer interior.

For additional information on vapor retarders, I recommend checking out NAIMA’s website[2], which has lots of useful information.

The wording has also been corrected in the digital edition[3] of the magazine.

Source URL: https://www.constructionspecifier.com/vapor-article-moving-from-interior-to-exterior/

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