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Enclosing an attic space to be insulated

I thinking about enclosing a walk-in attic space with insulation and putting in a register for A/C.  I live in Houston and understand they recommend no vapor barriers on insulation in my area.  If this is the case do you need an air barrier as well? Right now there is only the Hardi-Plank siding some Tarp Paper and that is it on the exterior wall.  Also, there is the gap between the brick veneer and the interior wall below.  Does anything special need to be done there to seal it up besides some insulation there? Wall Layout.jpg 

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Posted 2011-04-20T18:54:03+0000  by toddbx toddbx

Hey toddbx, welcome to the Home Depot Community!


Looking at a map for recommended vapor barrier installation, it looks like you may want to include a barrier on the outside of your insulated area.  See the map here:

This is also a good guide for standard insulating practices.


You do not need an air barrier like the one you describe.  Indeed, insulation itself is comprised of many small areas of trapped air.  The only thing to watch for are air leaks which should be caulked/sealed.


I hope this helps,


Posted 2011-04-22T15:22:33+0000  by Chris_HD_CHI

Any recomendations for what to use and how to install that vapor barrier on the outside since I don't have access to the outside?  Can I just put it between the studs from the backside?

Posted 2011-05-11T14:23:02+0000  by toddbx

Hey toddbx, thanks for coming back.

You have 2 areas drawn in the sketch.  Above the 2x8 joists there is tar paper under the siding, and this provides a quite good vapor barrier.  No action is needed here besides any insulation you want to add between the studs.


Below the joists the brick wall, its gap and then studs are a common building practice in the south as well.  The best place for a vapor and air barrier would actually be just where you show a “backing” behind the studs.  You can then apply insulation between the studs and then finish the wall.  I would use 4-6mil plastic sheeting if that “backing” is not waterproof.  This system will cause any condensation to form on the plastic barrier and drain down, keeping it off the brick and any insulation you install.  Here is a pdf file with more information:

I hope this helps,


Posted 2011-05-13T13:00:50+0000  by Chris_HD_CHI
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