Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Building & Construction

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 11-23-2008, 02:15 PM   #1
Newbie
 
Join Date: Aug 2008
Posts: 14
Share |
Default

Exterior Wall Insulation require plastic barrier?


While tearing down ceramic tile and rotted drywall in a bathroom shower repair I noticed that the pink fiberglass insulation had some slight black mold growing on it, so I am opting to replace those columns.

My house was built in the late 1970s and I noted that all of my exterior walls including this bath one had a aprx 2-3 mil thick piece of clear plastic over top of the insulation. This bathroom insulation appears not to be "faced" in that it is pink on both sides (no paper on one side).

I have 2x4 outside wall construction so I purchased R-13 PinkPro or ProPink insulation. Because this is the "good stuff" and is "faced", do I need to put a 2-3 mil thick sheet of clear plastic over top of it?

It is my assumption that because this is "faced" that if I staple the faced part interior so I can see it that is all I should require.

If it matters I will be putting cement board over top of the insulation when I redo the shower stall.

BillyDIY is offline   Reply With Quote
Old 11-23-2008, 04:11 PM   #2
Lic. Builder/GC/Remodeler
 
AtlanticWBConst.'s Avatar
 
Join Date: May 2006
Location: New England
Posts: 7,556
Default

Exterior Wall Insulation require plastic barrier?


Quote:
Originally Posted by BillyDIY View Post
....do I need to put a 2-3 mil thick sheet of clear plastic over top of it?....
No, since it is already "faced", you have a vapor barrier over it (kraft paper face).
Installing an additional vapor barrier over another one, is actually against building code, since such an arrangement will create an "envelope" to trap moisture.

AtlanticWBConst. is offline   Reply With Quote
Old 11-23-2008, 09:22 PM   #3
Newbie
 
Join Date: Aug 2008
Posts: 14
Default

Exterior Wall Insulation require plastic barrier?


Thanks Atlantic. Turns out on another forum I got the exact opposite advice so I did a little more searching and you are spot on.

http://saveenergy.owenscorningblog.c...raftfaced.html
BillyDIY is offline   Reply With Quote
Old 11-24-2008, 02:57 PM   #4
RDS
Member
 
Join Date: Feb 2008
Location: Northern New Jersey
Posts: 226
Default

Exterior Wall Insulation require plastic barrier?


On a similar subject: Is it true that one should not put greenboard over kraft-faced fiberglass insulation, for a similar reason? (i.e. to avoid creating a double vapor-barrier) I've read conflicting and/or unclear advice on this.

(Note I'm not talking about greenboard around a tub or shower or under tile -- just a regular exterior wall and ceiling, under attic, in a bathroom.)

Perhaps I should ask the more basic question: Is it overkill to use greenboard on a bathroom ceiling and/or on a bathroom wall that isn't directly part of a bath/shower enclosure?

Basically, since I've already put up the kraft-faced insulation and bought the greenboard but not yet installed it, I'm wondering whether I should (a) switch to unfaced insulation, (b) switch to regular drywall, or (c) neither.

Grateful for any guidance.

Last edited by RDS; 11-24-2008 at 04:12 PM. Reason: for clarity
RDS is offline   Reply With Quote
Old 11-24-2008, 04:02 PM   #5
Registered User
 
Termite's Avatar
 
Join Date: Apr 2008
Posts: 6,520
Default

Exterior Wall Insulation require plastic barrier?


RDS, don't confuse greenboard with a moisture barrier. It isn't. It is only different than regular sheetrock in that it is a little bit mold resistant. Greenboard is just fine to use in bathrooms, provided it isn't used in the wet areas (shower/tub walls).
Termite is offline   Reply With Quote
Old 11-24-2008, 04:35 PM   #6
RDS
Member
 
Join Date: Feb 2008
Location: Northern New Jersey
Posts: 226
Default

Exterior Wall Insulation require plastic barrier?


Thanks termite.

If 'greenboard as vapor barrier' is a misconception, it seems to be a common one. For instance, it turned up in this thread recently:
Green Board over Vapor Barrier?

and I first encountered it in Myron Ferguson's book Drywall, which seems to be a well-regarded source on the subject. On page 8 he says: 'no greenboard over a vapor retarder IF the board will be finished with tile, vinyl, or oil paint'; but later on the same page he says 'on ceilings, no greenboard over faced insulation, period'. For a remodeling newbie the advice out there is confusingly contradictory to say the least.

But when in doubt I'll stick with what the termite says.
RDS is offline   Reply With Quote
Old 11-24-2008, 04:48 PM   #7
Lic. Builder/GC/Remodeler
 
AtlanticWBConst.'s Avatar
 
Join Date: May 2006
Location: New England
Posts: 7,556
Default

Exterior Wall Insulation require plastic barrier?


I'll back up KCT, Green board IS NOT, in any way, shape, or form..... a moisture barrier.
AtlanticWBConst. is offline   Reply With Quote
Old 11-24-2008, 06:29 PM   #8
Drywall contractor
 
Join Date: Jul 2008
Location: Lilburn, GA
Posts: 2,094
Default

Exterior Wall Insulation require plastic barrier?


With proper ventilation and appropriate paint, there's no NEED to use greenboard at all in my opinion. I only use it if a customer insists. Since you have it, use it unless you WANT to exchange it. Regular rock is a little cheaper, but not enough to justify loading up the green and taking it back. Your faced insulation is fine.
__________________
If you can read this, thank a teacher. If you can read this in English, thank a soldier. Support our troops.
bjbatlanta is offline   Reply With Quote
Old 11-25-2008, 01:24 AM   #9
Residential Contractor
 
Join Date: Nov 2008
Location: Eastern WA
Posts: 24
Default

Exterior Wall Insulation require plastic barrier?


I would give using cement board another thought. Look into DensShield or DensGuard they are a far superior product and unlike Durock or WonderBoard they with not draw moisture in to them, CBU will wick moisture like nothin else if it can. Take a peek @ USG's website regarding the steps u have to take as far as vapor barriers behind when using the CBU products. Plus, the Dens products are very user friendly and more water resistant. No VB behind Dens a must have VB behind CBU per all manufacturer install specs.

Tracy.
Tracymc is offline   Reply With Quote
Old 11-25-2008, 07:46 AM   #10
Lic. Builder/GC/Remodeler
 
AtlanticWBConst.'s Avatar
 
Join Date: May 2006
Location: New England
Posts: 7,556
Default

Exterior Wall Insulation require plastic barrier?


Quote:
Originally Posted by Tracymc View Post
I would give using cement board another thought. Look into DensShield or DensGuard they are a far superior product and unlike Durock or WonderBoard they with not draw moisture in to them, CBU will wick moisture like nothin else if it can. Take a peek @ USG's website regarding the steps u have to take as far as vapor barriers behind when using the CBU products. Plus, the Dens products are very user friendly and more water resistant. No VB behind Dens a must have VB behind CBU per all manufacturer install specs.

Tracy.
Superiority of one product over another, is subject to interpretation, preference, and relative comparisons to particular characteristics of each material.

There is often confusion between "Vapor Barriers" (VB) and "Moisture Barriers" (MB).
FWIW - Both Denshield, and Cement Board, "are" neither.

Denshield "has" a moisture barrier coating applied to it's surface. Installed, it requires additional work, to "become" an actual vapor/moisture barrier system.

1.) Denshield loses any concept of a sealed surface, if you break the surface materials with a nail, or screw. Moisture will also be able to enter at any other broken/penetrated locations, as well as at any seams.

2.) With Denshield, you would still have to seal all seams and corners with a moisture proof material, once you install it, in order for it to be a "completely sealed barrier" (MB)...

Example; Denshield Installation Instructions - to seal seams and water penetration points:
"... 2” 10 x 10 glass fiber mesh tape–embed in a skim coat of material used to set tiles on all joints and corners that are to receive tile. Caulk or seal penetrations and abutments to dissimilar materials..."

3.) If you are getting water into any substrate material, you have issues already. The point is, that "if" water were to migrate behind the tile, you want mold and rot resistant material there.

4.) Your primary layer is to be installed water-tight. That encompasses, the proper installation of the tile, grout, and any caulking used. That is your primary water-tight surface. The substrate, is your secondary surface (for adhering the tile to).
With CBU -The VB is placed underneath the cement board, over the wood framing, to protect it, should the primary surface material (Tile/grout/caulk) fail for any reason.

IMHO - Whether that tile substrate material is your secondary VB/MB, or the VB/MB is behind a rot-resistant cementitious material (CBU), does not designate, nor does it classify, one material, as being superior to the other.
AtlanticWBConst. is offline   Reply With Quote
Old 11-26-2008, 08:41 AM   #11
Newbie
 
Join Date: May 2008
Posts: 12
Default

Exterior Wall Insulation require plastic barrier?


Would an additional vapor barrier behind densshield be a good thing or a problem?
joelbuckley is offline   Reply With Quote
Old 11-26-2008, 09:48 AM   #12
Lic. Builder/GC/Remodeler
 
AtlanticWBConst.'s Avatar
 
Join Date: May 2006
Location: New England
Posts: 7,556
Default

Exterior Wall Insulation require plastic barrier?


Quote:
Originally Posted by joelbuckley View Post
Would an additional vapor barrier behind densshield be a good thing or a problem?
Problem, don't install one if you are going to use DS
AtlanticWBConst. is offline   Reply With Quote
Old 11-26-2008, 11:39 AM   #13
Mold!! Let's kill it!
 
Join Date: Feb 2008
Location: Central Pennsylvania
Posts: 2,836
Default

Exterior Wall Insulation require plastic barrier?


As a little bit of back up to Atlantic's info:

(From USG's spec)
When tested in conformance with ASTM E 96, DensShield panels achieved a perm rating of less than 1.5 alone, 1.0 with dry set mortars and .5 when applied with a Type 1 tile mastic.

For comparison, the kraftpaper face on fiberglass batts have a permeability rating or .4 while 6 mil poly is 0.06.

Anything with a perm rating of 1.0 or less is considered a vapor retarder.
Maintenance 6 is online now   Reply With Quote
Old 03-05-2009, 08:12 AM   #14
Newbie
 
Join Date: Mar 2009
Posts: 2
Default

Exterior Wall Insulation require plastic barrier?


Unfortunately I made the mistake of installing 6 mil poly over kraft-faced insulation in a renovation a few years ago. What would my best coarse of action be? There are no signs of mold but I would want to prevent any problems from occuring down the road. Is it safe to keep it or should all the plastic be removed?
rdavis84 is offline   Reply With Quote
Old 03-05-2009, 10:19 AM   #15
Member
 
Join Date: Jul 2007
Posts: 1,523
Default

Exterior Wall Insulation require plastic barrier?


Quote:
Originally Posted by rdavis84 View Post
Unfortunately I made the mistake of installing 6 mil poly over kraft-faced insulation in a renovation a few years ago. What would my best coarse of action be? There are no signs of mold but I would want to prevent any problems from occuring down the road. Is it safe to keep it or should all the plastic be removed?
Best course of action is to not worry about it. No inside vapor is getting past the poly. If outside moisture vapor works it's way all the way through your wall the kraft paper will stop it. Yes in theory if you got moisture between these two layers it would take a long time to dry out so you don't want to intentionally do it this way. But in reality the chances of trapped moisture between these two layers that are essentially in contact with each other is remote. Certainly not worth tearing out drywall.

jogr is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
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
Cape Cod Style House Attic/Crawl Space Insulation Help Danielg Insulation 24 05-21-2012 08:20 AM
basement insulation and vapour barrier coolnes Remodeling 11 02-01-2009 08:56 AM
How important is plastic vapor barrier on foundation wall? slatergrl Remodeling 5 02-18-2008 12:49 PM
Vapor Barrier & Blown in Insulation barbe4 Building & Construction 1 12-03-2007 08:05 PM
Cathedral Ceiling Sweats Dan H Roofing/Siding 14 02-22-2007 11:40 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.