Go Back  DoItYourself.com Community Forums > Interior Improvement Center > Basements, Attics and Crawl Spaces
Reload this Page >

Vapor barrier needed with 2" Rigid Foam Insulation

Vapor barrier needed with 2" Rigid Foam Insulation


  #1  
Old 02-24-14, 09:25 AM
srburns's Avatar
Member
Thread Starter
Join Date: Nov 2013
Location: Canada
Posts: 5
Received 0 Votes on 0 Posts
Vapor barrier needed with 2" Rigid Foam Insulation

Hi All

Planning to redo a basement foundation wall. The plan is to use 2" Extruded Polystyrene Rigid Insulation against the foundation wall. Then build a typical 2x4 stud wall with bat insulation against the foam wall then drywall.

My question with this build is, do I need a vapor barrier on the stud wall before I hang the drywall? I have heard mixed views if it is needed since I will be using 2" foam.

I have looked at the sticky above, but all the links land on a generic home page.
 
  #2  
Old 02-27-14, 06:35 AM
srburns's Avatar
Member
Thread Starter
Join Date: Nov 2013
Location: Canada
Posts: 5
Received 0 Votes on 0 Posts
Anyone help me out with this? Toronto Canada area if it helps.

S
 
  #3  
Old 02-27-14, 07:19 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,524
Received 37 Votes on 34 Posts
Hi sr,
The real answer will come from your local code authority, which varies just as much as the opinions you have already found.

My position is no vapor barrier below grade to allow a small amount of drying through that 2" poly. 2" is not very permeable and some will consider it a VB. I've attached a link on vapor diffusion retarders. But vapor is much different from moisture. If you have or have had any water problems, they must be corrected first, usually (best) from the outside.

If a class I vapor retarder such as poly is applied to the inside at any point, you can expect the moisture directly behind the plastic to accumulate, all-be-it slowly, until it matches the soil outside and that is usually sufficient to grow mold. By allowing a small amount to pass through the foam, it reduces the moisture build up.

So, IMO, no additional VB is required. But many code officials will disagree.

I also attached a link on basements. Photograph 4 illustrates what you described and also answers your question.

Vapor Barriers or Vapor Diffusion Retarders | Department of Energy

BSD-103: Understanding Basements — Building Science Information

Good luck and sorry I didn't catch your question when posted.
Bud
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: