# Basement Vapour barrier issue.



## EasternCanadian (Dec 14, 2012)

First time poster here.

I recently purchased a home (in August) and performed a complete interior renovation. Now I am into the basement and have an issue I'd love some feedback on. There is a finished room in my basement that covers two exterior walls (28' and 12', all other concrete walls were exposed).

The basement walls in question are famed (with 2x4 studs) 1" away from the concrete with the top 4' insulated with R12, covered with vapor barrier. The finishing is 4' of tongue and groove pine on the botton and 3' of drywall on top. 

The Problem: the vapour barrier is trapping moister in the wall and there was a small mold/mildew issue in the corner of the room, i kicked a hole in the wall (the 12' portion is all drywall, hole is approx 2'X2') and it was soaked, but dried up in a few days because of the new air movement.

Solutions: I was wondering if installing a few grills along the bottom of the wall (4" hole saw through the pine, penetrating the vapour barrier) would allow enough air flow to solve the moisture issue.. thoughts?

hoping I do not have to strip the wall down to the studs just to remove vapour barrier.

FYI the portion of the basement i finished i glued foam to the foundation, framed with 2X4, batted entire cavity with R12, no vapour and drywalled.


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## EasternCanadian (Dec 14, 2012)

10 views, but no replies.. c'mon guys!!


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## oh'mike (Sep 18, 2009)

Yes,sir---

The best authorities on insulation--particularly Canadian--are at work---and will catch this when they get home---

I'll add my two cents--(two nickles in Canada)--Add several return air grills to allow some circulation of air behind the walls---on the new section--I'll wait till GBR--Home Sealed or Windows on Wash get home from work---

There are others that have knowledge---so you may get an answer right away----Mike--


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## EasternCanadian (Dec 14, 2012)

Ah yes, I like to work 4 10 hour days.. or 4 12's.. I assume everybody has the same weekend as i do hahah

Thx for the input. 

Another possibility is to carefully remove the bottom 4 feet of tongue and groove pine and install it again after removing the poly.


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## oh'mike (Sep 18, 2009)

That would help---I see Home Sealed is answering questions---I hope he has time and sees this---Mike----


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## Windows on Wash (Aug 30, 2011)

Lets assume that you don't have a bulk moisture infiltration (i.e. foundation issue) at this juncture. Grading and foundation condition (cracks, coating, drainage, etc) should be checked but if they are good lets move on to the more likely issue.

Warm moist air + cold concrete = condensation and moisture

Best bet is to seal up the bands with rigid foam/sealant combo or with CC SPF of at least 2-3".

Pull down the walls and put rigid insulation on the walls. 

Insulated the stud bays and don't use a vapor barrier (my opinion).

Drywall and make sure the drywall is airtight as a drum.


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## EasternCanadian (Dec 14, 2012)

Windows on Wash:

The portion of the basement I finished was exactly how you suggested.. 1" rigid foam glued with PL 300 tuck taped all seams, 2X4 framing with R12 then drywall. 

I suppose the best way is to strip the walls in the "old" area, I was hoping to find a "half hour - low cost" solution ha.


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## Windows on Wash (Aug 30, 2011)

No such luck my friend.

Tear it down and do it right.


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## EasternCanadian (Dec 14, 2012)

That's what I figured.. Was hoping to be convinced otherwise.


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## Windows on Wash (Aug 30, 2011)

EasternCanadian said:


> That's what I figured.. Was hoping to be convinced otherwise.


Sorry boss.

You probably knew the answer before you posted it.

In theory you could make it airtight and try that but that is a pretty impossible proposition with T&G. :wink:


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## Gary in WA (Mar 11, 2009)

I also recommend foamboard because it is moisture tolerant without loss of R-value when wet; http://archive.nrc-cnrc.gc.ca/eng/ibp/irc/bsi/90-controlling-heat.html

Depends on your location, season and indoor/outdoor humidity if poly v.b. will work or not. The condensed version: http://www.buildingscience.com/docu...ing-hygrothermal-modeling-basement-insulation

The extended version, complete with "double" poly layers: ftp://ftp.cmhc-schl.gc.ca/chic-ccdh...ngual/Vapour_Permeance_Volume_1_Web_sept5.pdf pp. 33-55 is note-worthy.

Gary


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## EasternCanadian (Dec 14, 2012)

Windows on Wash said:


> Lets assume that you don't have a bulk moisture infiltration (i.e. foundation issue) at this juncture. Grading and foundation condition (cracks, coating, drainage, etc) should be checked but if they are good lets move on to the more likely issue.
> 
> Warm moist air + cold concrete = condensation and moisture
> 
> ...



Thanks for the input. I agree 100% with your method of finishing a basement, NO vapor barrier and HAVING rigid foam glued to the concrete are the two "non-negotiable" procedures in my opinion. I like to insulate the entire stud bay with R12 in a 2X4 wall.. I know guys that do R20 in 2X6... or either of these with only batting the top 4'. 

I have one final question because you seem very knowledgeable. In the 'new' section I finished I Insulated the rim joist with a double layer of R12 on top of tightly cut pieces of rigid foam. I have yet to poly/acoustical the rim joist. I am intending of sealing the poly with acoustical to the top of rigid foam (maybe an inch or sow down the face) and all around the top and side of the cavity as usual.. thoughts or suggestions?


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## Windows on Wash (Aug 30, 2011)

Don't both with the poly.

Just spray foam or seal it with caulking.

Seal the connection between the sill plate and the poured wall as well.


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## EasternCanadian (Dec 14, 2012)

Windows on Wash said:


> Don't both with the poly.
> 
> Just spray foam or seal it with caulking.
> 
> Seal the connection between the sill plate and the poured wall as well.


Ahhh makes sense, the rigid IS the vapor barrier, seal around the edges and I'm good to go. Thanks very much for replying to my posts so quickly, very helpful. One final thing, do you think in the future using a double/triple layer of rigid foam would be the best way to insulate a rim joist? Or bats with poly/acoustical?


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## Windows on Wash (Aug 30, 2011)

Rigid foam or CC SPF.


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## laser_jock (Jan 26, 2013)

*no vapor barrier below grade!*

buildingscience is a good resource - basement finishes with vapor barriers below grade are failing. the water isn't condensing necessarily because of leaks in the vapor barrier, the water can be coming through the concrete from the soil outside, because that's what concrete does. Making the wall airtight will just make the problem worse. new construction is adding foam on the outside of the foundation wall before backfill.
you have to get that vapor barrier out of there. the rigid foam is semi-permeable, which is recommended to be glued directly on the concrete, then framed out with fiberglass (no vapor barrier).


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