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Old 04-12-2010, 03:37 PM   #1
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Vapour barrier and XPS: Continuing Previous Owner's Rennovation


Hello, first let me mention that I've been reading up on a lot of the threads here as a guest and I'd like to say I've always been impressed with all the info and good discussions.

I'm a first-time homebuyer in Quebec (Canada) and my house has a semi-unfinished basement ... semi being in that the previous owner started some insulation / drywalling but never completed the work before he sold me the house. I had done a bit of research and I was wondering if what he did (or had done) is legit and if I can continue the finishing of the basement. Here's what I see in the basement, starting from the outside in:

- Cement wall of foundation
- 2" thick XPS Cladmate panels bonded on to the wall (no taping of joints)
- 6 mil vapour barrier
- 2x3 stud walls

The stud walls hold the VB against the Cladmate and the VB runs underneath the bottom plate of the wall to keep the wood from contacting the cement floor. The above grade parts of the wall look to be incomplete, there is no insulation in the rim joist area and the VB sort of folds back and is left loose and hanging over the top of the stud wall.

Seeing as there is a good thermal break and a moisture barrier between the stud wall and the warm side of the XPS, my plan is to continue with this method since it covers half od the bsement wall, then add batt insulation in between the studs and finish it with drywall.

The inspector who checked out the house said it was up to code but that the "situation needs to be rectified ASAP" due to the exposed insulation which is combustible. He didn't give any other instructions with respect to the joists and VB.

I'm just a bit confused as to why the VB sheet was used instead of Tuck taping the joints on the panels? The XPS is technically not acting like a vapour barrier now, so what should I do to seal everything up, escpecially at the top/joist area?

I'd appreciate any of your expert input as I'd like to get this closed up as soon as possible.

Thanks in advance!

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Old 04-12-2010, 04:03 PM   #2
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Vapour barrier and XPS: Continuing Previous Owner's Rennovation


Usually you'd have the cement walls, wood studs (or metal) with the appropriate insulation inbetween the studs, then the vapour barrier. And, yes, there should be a sill trim (or plastic) under the bottom of your wall ... where it comes in contact with cement. Or, you could get away with treated lumber. The vapour barrier should create a seal right around the entier room. If you plan to insulate the ceiling, seal that as well. A little hint: if you need extra wiring, do it soon rather that aftrer the fact.
Carry on you're on the right path.

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Old 04-13-2010, 07:00 AM   #3
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Vapour barrier and XPS: Continuing Previous Owner's Rennovation


Thanks for the feedback Mark. I think the previous owner was going for a very high R-value, hence the double insulation (R-10 XPS + batt insulation filling the stud walls). The basement gets quite cold in the winter.

So I guess the best strategy is then to continue around the walls as-is and for the top would be to insulate the rim joists and then seal it off with the vapour barrier, taping all the ends?

I will probably add more batt insulation in the joists (mostly for sound proofing) but have a licensed electrician pass all the wiring first in the walls / ceiling.


One note - using treated lumber indoors is against code in my area so unfortunately I wll have to just use standard 2x3s...
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Old 04-13-2010, 08:32 AM   #4
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Vapour barrier and XPS: Continuing Previous Owner's Rennovation


what location are you in?
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Old 04-13-2010, 09:31 AM   #5
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Vapour barrier and XPS: Continuing Previous Owner's Rennovation


Quote:
Originally Posted by Bob Mariani View Post
what location are you in?

Quebec (Canada)


I've updated my profile now, thanks!
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Old 04-13-2010, 11:19 AM   #6
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Vapour barrier and XPS: Continuing Previous Owner's Rennovation


then seal the XPS with spray foam. And the vapor barrier goes under the drywall.
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Old 04-17-2010, 10:53 PM   #7
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Vapour barrier and XPS: Continuing Previous Owner's Rennovation


Quote:
Originally Posted by interdit_450 View Post
Thanks for the feedback Mark. I think the previous owner was going for a very high R-value, hence the double insulation (R-10 XPS + batt insulation filling the stud walls). The basement gets quite cold in the winter.

So I guess the best strategy is then to continue around the walls as-is and for the top would be to insulate the rim joists and then seal it off with the vapour barrier, taping all the ends?

I will probably add more batt insulation in the joists (mostly for sound proofing) but have a licensed electrician pass all the wiring first in the walls / ceiling.


One note - using treated lumber indoors is against code in my area so unfortunately I wll have to just use standard 2x3s...
I believe that you have stated that the vapour barrier is against (on top of) the XPS.
And its your intention to add more insulation between the wooden studs.
The vapour barrier must be placed on the warm side of 'ALL' insulation. Otherwise, moisture from inside the house may infiltrate the first layer of insulation and condense on the vapour barrier surface, thus allowing mold to develop.
I would think that the V/B against the XPS should have multiple perforations made, so as to allow it to breath.
The vapour barrier should be placed over the insulation between the studs in the usual manner.
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Old 05-04-2010, 08:42 AM   #8
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Vapour barrier and XPS: Continuing Previous Owner's Rennovation


Thanks for all the comments and feedback – just wanted to update you and anyone else who was interested in this thread and share some info I received. I used the info and feedback on this site to file for my permit to the finish the basement and got the city inspector to take a look, some corrections were suggested.

No vapour PE barrier is required if I keep the 2” XPS foamboard insulation continuous along all the walls, extending from the floor all the way up the inside wall above grade, but I must Tuck Tape and seal all the joints. Once sealed, this is sufficient to be my vapour barrier and also my thermal break. From the outside, moisture from the foundation wall (either from groundwater pressure or capillary action through the cement) will not be able to penetrate into the living space and the XPS will not hold any moisture either. The cold face of the XPS will be at the same temperature as the wall so there is no risk of condensation forming. From the inside, the warm face of the XPS will be at the same temperature as the inside of the house so again there will be no chance for warm inside air to make contact with a cold surface and form condensation. Extra batt insulation can be added afterwards but it really is optional (if I’m really aiming for a high R-value on the wall).

If I do the above method, adding a second vapor barrier under the drywall will only trap any moisture that does get in there (capillary action, small air leaks from punctures or unintentional gaps in the barrier) inside the stud wall.

She suggested the previous owner had a vapour barrier over the XPS because of two primary reasons. First of all, he had reduced to 1” thickness in certain areas to fit insulation behind some drain pipes that were about 1.25” from the wall. 1” XPS is not enough to form a vapour barrier on its own. Secondly, the joints between the foamboard were not taped. She recommended I lock down the loose edges of the moisture barrier and then leave as-is.

While there is no real problem with the standard batt insulation and inside vapour barrier construction method in the code, she did not recommend it in my area due to the year of build of my house, soil conditions and relatively high water table (i.e. lots of moisture available out there beyond those foundation walls, minimal waterproofing done on the foundation exterior when the house was built).

The problem she’s been finding with vapour barriers installed under the drywall in my area is that they have a tendency of trapping moisture inside the stud wall and insulation cavity (take a look at the attached photo she referred me to on the internet for an extreme case). A stud wall with that arrangement below grade will not dry to the outside quickly enough and with the vapour barrier installed cannot dry to the inside either. This leads to mold and poor air quality.

People with unfinished basements (such as myself) probably look at their dry foundation walls and think they have no moisture coming through or perfect water-proofing, but in reality there is always movement from cold to hot, wet to dry. No foundation is waterproof. Direction and volume of vapour movement changes with the time of year as well. The bare walls appear to be dry because (with no moisture barrier) the cement always drys out to the ambient air in the living space should moisture be absorbed from outside sources.



So it looks like taped and sealed XPS is the way to go…the question now is should I add batt insulation or not in my stud wall? I imagine the extra R value wouldn’t hurt plus it would be good for acoustic damping. Any thoughts on this or what the inspector said or anyone already have this insulation arrangement in their basement?
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Old 05-04-2010, 09:52 AM   #9
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Vapour barrier and XPS: Continuing Previous Owner's Rennovation


Thanks for the feedback. I am in Alberta which is much dryer, but what your inspector suggested makes sense. I used to live in Montreal so I can appreciate the moisture issues. As to adding more insulation, it sounds as if it's just a judgement call. It would add some benefit, but is it worth the expense? If the dollars aren't an issue, I'd go for it ... just for the added piece of mind.
Have a good one.
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Old 05-04-2010, 11:59 AM   #10
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Vapour barrier and XPS: Continuing Previous Owner's Rennovation


Whoops, here's the photo I forgot to post in the previous message.

You can see the mold trapped behind the 6 mil vapour barrier growing on the batt insulation and the wood studs. This leads to smells and poor air quality.





Courtesy of my inspector who referred me to http://www.nachi.org/forum/f18/poly-...t-walls-26852/

Remember: the vapour barrier installation approach may vary based on your local climate, surrounding soil moisture conditions, year of build & the foundation construction method of your house. I live in Quebec, Canada.

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