Vapor Barrier Issue Between Crawl Space And Conditioned Basement - Insulation - DIY Chatroom Home Improvement Forum

Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Insulation


Thread Tools Display Modes
Old 10-10-2012, 09:11 AM   #1
Join Date: Feb 2009
Location: Southern Ohio
Posts: 33
Rewards Points: 31

Vapor barrier issue between crawl space and conditioned basement

Ok, I know I have a problem, just not sure what to do about it. Although I've read a million vapor-barrier articles online, I'm still confused.

Between the unheated crawl space and the rest of the basement is that poly sheathing, completely sealed from ceiling to floor. This was originally done to keep the unconditioned crawl space separate from the rest of the basement. It is secured at the top with nails and then caulking and expanding foam, so there is absolutely no air penetration between the basement area and the crawl space. Then, next to this barrier, the basement wall was built. Then, batt insulation was put in the 2x4s, with the kraft paper facing the basement.

The way I see this, is there is insulation with vapor barrier on both sides, which is a problem.

Also, the wall that I am referring to (between the basement and crawl space) is the bathroom wall with a shower on it.

The room is not finished, and there is no drywall. Just studs with fiberglass batts in them.

Unless it's absolutely necessary, I don't want to remove the poly sheeting seperating the crawl space from the basement. If I just remove the kraft paper from the batts, do I have to worry about moisture going through the wall and getting into that insulation, since a shower is on that wall?

What should I do???



gregsenne is offline   Reply With Quote
Old 10-10-2012, 07:38 PM   #2
Exterior Construction
Windows on Wash's Avatar
Join Date: Aug 2011
Location: Washington DC Metro Area (VA, MD, DC)
Posts: 16,310
Rewards Points: 5,554
Blog Entries: 5

If you don't want to pull the poly, just put some unfaced fiberglass in there.

The poly is a class 1 vapor retarder and should not, if sealed properly, allow any moisture into the living space. Theoretically, moisture that get around via air leaks past the kraft facing, will not be able to dry out but I am not sure that is even and issue.

The vapor resistance of the kraft paper might keep some of the diffusion from the shower moisture but it will not have anywhere to dry to at that point.


Windows on Wash is offline   Reply With Quote
Old 10-10-2012, 09:12 PM   #3
Join Date: Feb 2009
Location: Southern Ohio
Posts: 33
Rewards Points: 31

So I should just take the Kraft paper off of the existing insulation, and hang drywall over it?

I was only concerned because I know my 1st floor has insulation in the outside walls, then the poly barrier, then drywall. And this would be backwards in the basement.
gregsenne is offline   Reply With Quote
Old 10-11-2012, 11:53 PM   #4
Registered User
Join Date: Mar 2009
Posts: 11,730
Rewards Points: 526

The paper facing will stop most of the moisture trying to go to the crawlspace (doing its job well). The poly sheeting will stop all moisture going either way. Ideally, I would replace the poly with foam board for its insulating qualities will keep the wall cavity below the dew point for no condensation (wall cavity is warm). Because the poly has no insulating value, you run a great moisture risk from exfiltration of the bathroom air condensing on the poly wetting the fiberglass losing 60-70% R-value;

ADA the drywall:

Paper facing has variable perms, it lets more moisture through the wetter it gets (it would still dry to the inside room), poly is bad:

Deep-six the poly with no insulating qualities, and add f.b. The paper facing can be left on IF the f.b. is thick enough, read page 2 and notice the varying thicknesses with varying perm interior vapor retarders, pp. 10-14 for your Zone 5 location: It all hinges on if the cavity is warm enough to prevent condensation due to R-value of the foam for the degree of interior vapor retarder.

Foil-faced (pp.14) is acceptable left exposed in most crawl spaces, check with your local AHJ on fire code requirements to make sure. OR, reuse the poly (over unfaced f.b.) if f.b. is thick enough, still need an ignition barrier on crawl space side.

If any ads are present below my answer or words underlined/colored, I do not condone/support/use the product or services listed/linked to, they are there without my consent.
17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?
Gary in WA is offline   Reply With Quote

Thread Tools
Display Modes

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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Odor from Crawl Space G Ollis General DIY Discussions 68 11-02-2013 01:31 AM
Conditioned Crawl Space Insulation LuckyFoot15 Insulation 4 09-30-2012 01:35 PM
Conditioned Crawl Space - Advice re Waterproofing AND Int or ext insulation JohnNe Building & Construction 4 02-10-2012 06:53 AM
conditioned crawl space, drk HVAC 12 01-20-2011 05:06 PM
Crawl Space Moisture jim007 General DIY Discussions 8 09-21-2010 06:53 PM

Top of Page | View New Posts


Search Engine Friendly URLs by vBSEO 3.6.1