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-   -   Insulation - Faced or Unfaced? (http://www.diychatroom.com/f19/insulation-faced-unfaced-7171/)

Ricky D 03-17-2007 01:51 PM

Insulation - Faced or Unfaced?
 
Hi all - new user with a question about interior insulation.

I am Owner-Building a house located in the Sierra at 5000 feet elevation. Temps range from lows in the 20s to high in the 80s with low humidity levels year round.

The house is 2x6 stick framed with OSB exterior sheathing covered with Tyvek housewrap topped with furring strips supporting T&G cedar siding.

I am ready to install wall insulation and my question is this - do I use faced or unfaced batt insulation for the walls?

Reason I ask is that I am concerned about creating a moisture pocket in the exterior walls by having a double vapor barrier.

Meaning that the Tyvek on the exterior acts as a VB - would faced batts on the interior side of the space act as a second VB and possibly trap moisture within the wall?

Or do I want faced batts to seal interior moisture away from the wall cavity?

Thanks.

Rick

BigJimmy 03-17-2007 02:00 PM

Tyvek acts as an air barrier (and a barrier to moisture infiltration due to driven rain). It is moisture permeable however and will allow vapor movement out of the wall cavity.

AtlanticWBConst. 03-17-2007 02:24 PM

Quote:

Originally Posted by BigJimmy (Post 37294)
Tyvek acts as an air barrier (and a barrier to moisture infiltration due to driven rain). It is moisture permeable however and will allow vapor movement out of the wall cavity.

"... It 'acts' like a vapor barrier..."

- BigJimmy is right about this. (It works like Goretex clothing)....


http://en.wikipedia.org/wiki/Tyvek

From the link above:

"Water vapor can pass through Tyvek, but not liquid water"

To answer your question...use faced insulation for the walls...Face the paper towards the warm areas.

Ricky D 03-17-2007 02:26 PM

DUH - you're right - Tyvek does allow vapor to migrate outward. So that would mean that faced batts would be fine for the exterior wall cavities.

Makes sense.

Thanks.

BigJimmy 03-17-2007 05:29 PM

Quote:

Originally Posted by Ricky D (Post 37300)
...So that would mean that faced batts would be fine for the exterior wall cavities.

Unless I'm mistaken, it's the only application where it makes sense. On the other hand, I've seen people install unfaced batts in exterior cavities with 4-6mil poly laid over the studs to act as a vapor barrier. Whichever, the goal is to have the VB on the warm side to prevent the diffusion of moisture into the wall cavity where it can cause mold, rot, etc.

Good luck and take care!
Jimmy

joasis 03-17-2007 08:47 PM

And you could find a contractor that blows cellulose...wet blown in the walls or glue set. Perfect fill and no barrier needed. In my area, we charge .65 a sq/ft for 2X6 walls..and the R value is better then batts....green material also....


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