Go Back  DoItYourself.com Community Forums > Interior Improvement Center > Insulation, Radiant and Vapor Barriers
Reload this Page >

Insulation and vapor barrier for external walls in Dallas area?

Insulation and vapor barrier for external walls in Dallas area?

Reply

  #1  
Old 08-16-13, 09:56 PM
Member
Thread Starter
Join Date: Aug 2013
Location: USA
Posts: 4
Insulation and vapor barrier for external walls in Dallas area?

Hi -
Just purchased a home in the DFW area, and found moisture in some exterior walls. As I repair them, I'm struggling with what type of insulation to use. Pulling out the old drywall and insulation I was surprised to find plastic over faced insulation. Working my way from inside to outside, I have drywall --> plastic sheeting --> faced insulation, with facing toward interior --> exterior sheathing.

First question - should I use faced insulation again? And if I do, should the kraft paper go to the inside or outside (of the wall)? While faced insulation (facing indoors) makes sense in colder areas, it seems logical (to me) to have the paper facing out (i.e. to better keep the moisture/humidity out of the wall altogther.

Second question - do I really need the plastic under the drywall? My fear is that I'm trapping moisture in the wall with it...especially since it does get hot here in the summer.

Knowing the materials and order of them in the current scenario, I'm looking for info about how to put these walls back together - thanks for any help!
 
Sponsored Links
  #2  
Old 08-17-13, 02:49 AM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,968
Welcome to the forums! What is happening is you have two vapor barriers. You only need the kraft facing OR the plastic, not both. I would opt for kraft facing alone, facing the warm side (inside).
 
  #3  
Old 08-17-13, 07:09 AM
Member
Thread Starter
Join Date: Aug 2013
Location: USA
Posts: 4
Thank you! I thought the plastic seemed unnecessary...I'll go with the faced insulation on the interior. Wonder if the dual VB's were creating another issue with moisture?
 
  #4  
Old 08-17-13, 06:02 PM
Member
Join Date: Mar 2013
Location: USA
Posts: 457
The plastic was stopping the warm exterior air, condensing on the cavity insulation. NO PLASTIC anywhere, unfaced batts are suggested for your location;Info-310: Vapor Control Layer Recommendations — Building Science Information No faced-insulation is required per code, either; Chapter 14 - Exterior Walls

Gary
 
  #5  
Old 08-20-13, 10:32 PM
Member
Thread Starter
Join Date: Aug 2013
Location: USA
Posts: 4
Great article - thank you! I've been considering using closed cell foam insulation as a base on the exterior, then topping with insulation. My reasoning = stop as much air flow/moisture from entering the walls altogether. Given this info, I'd put unfaced insulation on the inside. Working my way from inside to outside, I'd have drywall --> unfaced insulation --> ~1" closed cell foam insulation --> exterior sheathing. Thoughts?
 
  #6  
Old 08-22-13, 12:15 PM
Member
Join Date: Mar 2013
Location: USA
Posts: 457
The sheathing may get wet because the foam only allows drying to the exterior. Better if f.b. is exterior to sheathing, stopping moisture RH there. Sheathing could`still dry to inside (if ever wet), if needed; http://www.buildingscience.com/docum...nd-wall-design

http://www.buildingscience.com/docum...ting-sheathing

Gary
 
  #7  
Old 08-22-13, 11:03 PM
Member
Thread Starter
Join Date: Aug 2013
Location: USA
Posts: 4
I was thinking spraying a closed cell foam vs using a foamboard. Wouldn't that seal the cavity (i.e. sheathing and studs)? Thinking a sealed cavity would decrease the chance of moisture ever entering. And perhaps let the wall dry from the inside if any did get in (from the inside).
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes