# Type-1 Vapor Barriers?



## jpranch (May 1, 2012)

We are in climate zone 6B. It is very dry here. Yet we have had some pretty bad mold issues. Three years ago we prohibited the use of 6 mil poly (Type-1 vapor barrier) from use on below grade walls. We are considering prohibiting the use of type-1 barriers for all residential construction. Are thinking is that the barrier must have a perm rating and allow the house to breath.  Question: Dose any current code already prohibit this? Is this an over reaction or are we missing something here?


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## Francis Vineyard (May 1, 2012)

What code year? Your method is in-line with the 2009 IRC, but I don't know where it is in the 2012!  This exception was not in 2006;

*R601.3 Vapor retarders. *Class I or II vapor retarders are required on the interior side of frame walls in Zones 5, 6, 7, 8 and Marine 4.

*Exceptions:*

1. _Basement walls_.

2. Below _grade _portion of any wall.

3. Construction where moisture or its freezing will not damage the materials.

*VAPOR RETARDER CLASS. *A measure of the ability of a material or assembly to limit the amount of moisture that passes through that material or assembly. Vapor retarder class shall be defined using the desiccant method with Procedure A of ASTM E 96 as follows:

Class I: 0.1 perm or less

Class II: 0.1 < perm ≤ 1.0 perm

Class III: 1.0 < perm ≤ 10 perm

Francis


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## Francis Vineyard (May 1, 2012)

Because the earlier codes did not prohibit vapor barriers below grade I used to provide this handout for residential projects.

“Because of this, it is important to maintain the drying potential of the wall since one never knows if the long-term moisture drive will be from the outside or the inside. A masonry wall is capable of absorbing large quantities of water due to the capillary action of concrete. If the masonry wall unit has hollow cores, air movements within the wall also increase the thermal and moisture movement. For this reason, it is recommended that a vapor retarder not be used in a wall that is partially or fully below grade.”

http://www.insulate.org/tb6.pdf

Francis


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## mtlogcabin (May 1, 2012)

Get the book titled

Builders Guide to Cold Climates

http://buildersguidecold.buildingsciencepress.com/

It is better and more pratical than the code books


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## GBrackins (May 1, 2012)

remember there is a difference in a vapor barrier and a vapor retarder. vapor barrier seems to get used like calling a circular saw a skil saw.

my understanding is a vapor barrier is a class I vapor retarder, such as sheet polyethelyene that would be used under a concrete slab. It is used to stop moisture movement on one side of the assembly.

a vapor retarder is used to allow controlled movement of moisture,

class II are such items as kraft paper backing on insulation and polystyrene insulation board

class III are such items as plywood and latex paint.

using the wrong one can lead to real problems as we all know.

great site to explore and learn  http://buildingscience.com/  John Straube and Joseph Lstiburek are a couple of phd's that are a riot in classes that teach. Surprised because I figured they would be stuffy and not able to relate building science to the real world.


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## jpranch (May 5, 2012)

Thanks evetybody.


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