[SlacK4]

Hello, I'm new to the forum, have a question regarding builder installed wrap insulation (r12) in the basement of a end unit townhome, in Hamilton, ON.

I recently purchased the unit and am now finishing the basement. The unit is 5 years old. The builder wrapped all walls from the bottom of floor joists to 1' above concrete floor. On two of the exterior walls I have noticed that there is a small amount of condensation behind the poly vapor barrier right at the mid level strapping. (light pink is now dark pink) and the previous owner cut little slits in the vapor barrier to allow the insulation to breathe.

I was hoping to keep this insulation on the wall and just stud right against it, as I don't want to have to dispose of it, but I now don't know if that's the right thing to do? I don't have a huge budget so I want to insulate the most cost effective way possible. But of course I don't want to do anything that may encourage mold.

I've heard of people cutting "X's" in the existing vapor barrier and leaving it on the wall. Then studding up against it, filling cavity with batts, then vapor barrier on studs, then drywall.

We currently use the basement even though it is not finished. It is warm and dry. (besides the small amount of condensation in the walls)

Any thoughts?

Thanks!

 

[Windows on Wash]

Pull it off, clean the wall, install rigid foam, frame the wall.

What you are referring to is probably PSK (poly skrim insulation) is about the worst application for a cold climate that you can do.

http://buildingscience.com/documents/digests/bsd-103-understanding-basements?full_view=1

 

[SlacK4]

Thanks for the reply, I was worried about that. The wrap is an R12 foundation blanket, not sure if it is PSK.

After I put up the rigid board, then stud, should I fill the cavity with batts and then vapor barrier? Should I do this to the whole basement, or just the exterior walls that show some condensation?

Thanks,

 

[Windows on Wash]

You will have to fill it via what your local code enforcement will require, however, many times you can show them that sufficient foam board thickness (and type of facer) will qualify as the vapor control layer.

You should fill the cavity with insulation.

 

[SlacK4]

Great, ill move forward with the rigid boards. To save money on purchasing batts, I am going to use the insulation I pull of the wall to fill the studs. Ill just cut it to 16". Any issues with this?

 

[mikegp]

If the insulation has already had moisture in it then it may have lost some r-value. I would personally get Roxul or similar as it deals great with moisture and fire.

 

[Gary in WA]

Few months ago, another basement in Ontario; http://www.diychatroom.com/f103/insulating-basement-ontario-eps-batts-324833/

Same advice, foam board without a vapor barrier interior polyis fine, but always check AHJ; http://www.nrcan.gc.ca/energy/effic...ng-the-heat-in/basement-insulation/15639#a6-2

Notice the different application for interior insulation, per code, here is another if FB is too much $$$; http://www.roxul.com/files/RX-NA_EN/pdf/ComfortBoard ISBasement_Eng.pdf

And another builder's take on that one with adjustments; https://www.google.com/url?sa=t&rct...sg=AFQjCNFihWruFRtcUxT69Jt2X7jykMDFpA&cad=rja

Foamboard is the safest, most expensive way to insulate the basement, but not the only way. It is interesting that there are so many ways that work just fine, but there is now a big push for foam board as the "only way" possible, at least in the U.S on a lot of forums. Anyone have any links to field testing of basement insulation that failed in US, not just computer simulations (which never match real-world testing- esp. on how warm the basement soil is), other than FG blanket-solid poly wrapped? Thanks...G.

Don't forget the wood rims, IMO, use foil-faced XPS to stop winter/summer time condensation keeping the wood wetter longer; http://www.diychatroom.com/f103/insulate-rim-joists-canned-spray-foam-roxul-307313/

Add some ff XPS under the bottom plate to stop air/moisture/wicking through the slab/room to wood, non paper-faced drywall with ADA, and galvanized nails in the framing. Use fiberglass duct tape/mastic on the joints rater than sticky tape as the XPS does shrink, allowing air to the concrete wall. The wet FG will dry to regain its full R-value, use it in the walls or attic. Not really required if XPS is per code as the empty cavity will be controlled by the HVAC system- depends on local amendments- remove the facer.

Gary

 

[TheSrProgrammer]

I spoke with somebody in the remediation field concerning mold in basements, and he said it's best to frame out the walls with air space between the basement wall and the studs - furring strips on the walls are less advisable because they don't allow for adequate air flow, potentially trapping moisture and facilitating mold growth. While that will marginally reduce the square footage of the finished space, it should pay dividends in cutting down on the likelihood of mold growth.

 

[Windows on Wash]

I spoke with somebody in the remediation field concerning mold in basements, and he said it's best to frame out the walls with air space between the basement wall and the studs - furring strips on the walls are less advisable because they don't allow for adequate air flow, potentially trapping moisture and facilitating mold growth. While that will marginally reduce the square footage of the finished space, it should pay dividends in cutting down on the likelihood of mold growth.

I will disagree with your person in the remediation field.

An air space doesn't mean diddly squat if there is a class 1 vapor retarder on both sides. All the air space give you at that point is a nice gestation zone.

 

[TheSrProgrammer]

The remediator seemed to feel that vapor retarders tended to trap rather that block moisture and that much of the remediation work he performed involved ripping out failed retarder installs. I believe his preferred approach was to coat the walls with a chemical sealant, purchase a high quality whole house dehumidfier, and allow for the air to circulate freely with the space between the walls and the back of the drywall. I am not sure or not if this advice is perfectly sound or complete in scope, so if it's incorrect it is likely due to my misinterpretation or lack of knowledge.

It is worth noting this remediator probably is the most successful one in the SE Pennsylvania region and has been in businness for nearly 20 years. There has been more than enough time and customers over the years to call him out as a hack if he was doing a bad job. Even if unconventional, his approach isn't without experience to back it up. And it wouldn't be all that surprising that the generally approved approach in the industry turns out to backfire more than help. Lead and asbestos come to mind...

 

[Windows on Wash]

Disagreeing with him on the science doesn't mean that I was inferring he was a "hack".

Any chemical sealant on the wall is likely approaching or already a Class I vapor retarder. At that point, the wall is only drying to the interior. If he is leaving an air space, in my opinion, the dominant drying vehicle is the fact that the the heat loss into the interstitial air space is keeping the surface temps up so that they aren't even reaching dewpoint and any moisture is allow to dry through to the drywall.

While all of this may work, it does not exactly line up with what we refer to as "efficient" building.

Foam (rigid of spray) is a widely accepted insulation material for the cementitious foundation walls. At that point, your surface temps are mitigated because the wall surfaces are warmed up a good bit. Depending on the type of foam or facer, the wall is designed to dry to the interior again.

If you have too little foam and too much interior wall insulation, you can slow the heat transfer to that surface and create a cold zone. If the interior wall leaks air...you will have issues. I don't think that the presence or lack of air space will ultimately make any difference here.

This is one of Gary's links that he references a good bit.

http://joneakes.com/jons-fixit-database/743