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Discussion Starter · #1 ·
Tonight I bought some Perma "R" 1" foil faced insulation at Lowes for my basement walls. I was doing some reading tonight and I read that I don't want the foil faced insulation on the entire wall because it will prevent the concrete walls from letting moisture escape. The basement is 30 years old. Should I return what I bought and instead get the pink XPS or could I just cut some slits in the foil paper to allow moisture to pass thru? Thanks.
 

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I just finished insulating my basement with XPS this past weekend...there's a discussion of it in my thread that might be worth a quick browse.


I found this document very useful - it might help with your moisture barrier questions. http://www.eere.energy.gov/buildings...s/db/35017.pdf . Rigid foam (with or without foil) acts as a moisture barrier, so neither type will let the concrete breathe. However, I also don't think that's a major issue - as long as you have a thermal break/moisture barrier, there will be nothing for vapor to condense on (mold won't grow on XPS), so you should be all set.


I apologize if I'm giving you info you already know, but be sure to use PL-300 or another foam board-safe adhesive. Many adhesives will burn through the foam board over time. PL-300 is specifically formulated for rigid foam application and won't do this.


I'm not sure, but in my shopping I think I found that there's also a significant cost savings with the unfaced stuff. I was able to insulate about 50 feet of wall space (26 2' x 8' panels) with 2" XPS, including Tyvek barrier tape and wayyy too much PL-300, for about $400. I don't know the R value of the stuff you purchased, but 2" XPS is R10, 1" is R5. If you want to use 1" XPS, the price would be only half...


Good luck with your project!
 

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Discussion Starter · #4 ·
According to that article, it is advised to use foil faced on the top half of the wall and XPS on the lower half to allow the concrete walls to dry to the interior.

Attachment 194222
 

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Quote:
Originally Posted by stepyourgameup
According to that article, it is advised to use foil faced on the top half of the wall and XPS on the lower half to allow the concrete walls to dry to the interior.

Attachment 194222
SYGU....that particular method is one of several acceptable ones in that article, and is described as the "fastest and most cost effective way to provide insulation" in the area with the greatest impact.


Using 2" thick rigid EPS panels on the entire wall is also acceptable, as described in the following page or two.
 

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Yes - I used the method in figure 15 as I have the 1" Enka drain around the perimeter of my basement. Sorry - guess I could have been more clear there. There are some good options provided in that article.
 

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Discussion Starter · #7 ·

Quote:
Originally Posted by AirBenji /forum/post/19653092


Yes - I used the method in figure 15 as I have the 1" Enka drain around the perimeter of my basement. Sorry - guess I could have been more clear there. There are some good options provided in that article.

As far as cost goes, it is about the same between the EPS and XPS.
 

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I am about ready to put start with my framing in my basement. I have poured concrete walls. I live in chicago, so we experience a very hot climate in the summer, and a very cold climate in the winter. I have read so much conflicting info about insulating, and vapor barriers, that my head is spinning.

Anyone have any suggestions?
 

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Quote:
Originally Posted by CatBrat /forum/post/19654491


Grabbing your head with both hands will many times stop the spinning.

I prefer just laying on my stomach



speedin....just go with 2" XPS entire wall like the document says and don't stress out about it anymore. You'll be far ahead of how I did it.
 

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Quote:
Originally Posted by fotto /forum/post/19654633


I prefer just laying on my stomach



speedin....just go with 2" XPS entire wall like the document says and don't stress out about it anymore. You'll be far ahead of how I did it.

Ok so the xps the entire wall, by gluing it and taping the seams?

What about a vapor barrier? So much conflicting info on whats right and wrong.


Side note....xps boards that are 2" are almost $24 bucks a piece!! at home depot..wow thats expensive, had no idea they were that expensive. I was thinking more along the lines of $10 bucks a board...but $24 is going to cost me a small fortune to do in my basement...
 

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Quote:
Originally Posted by speedin /forum/post/19654665


Ok so the xps the entire wall, by gluing it and taping the seams?

What about a vapor barrier? So much conflicting info on whats right and wrong.


Side note....xps boards that are 2" are almost $24 bucks a piece!! at home depot..wow thats expensive, had no idea they were that expensive. I was thinking more along the lines of $10 bucks a board...but $24 is going to cost me a small fortune to do in my basement...

If you plan to do standard 2x4 framed walls interior to your foundation walls, based on diagram 14 in the document noted previously, you should use standard unfaced batts (no Kraft facing for vapor barrier). I personally consider this the gold standard at this point and regret not doing it myself. Yes, you should tape the seams as that is what's helping to provide the vapor barrier.


XPS is a semi-permeable material...it lets water vapor though so your concrete wall will breathe, yet has insulation value which increases the interior surface temperature of the XPS compared to the the cold concrete wall preventing condensation and possible mold growth. That's my understanding at least.


As far as what I have read, you can use a lessor thickness of xps (1 inch) but that will obviously affect your R value and lesson your overall insulation. Other than that, I haven't seen any data suggesting any other adverse effect.


The use of 1 vs. 2" thick xps will ultimately be your decision to make. I would however consider your block/poured wall construction as part of that. Did your builder put exterior XPS on the walls before backfill, did they inject expanding foam into the walls (they did on my block walls) etc. Those (and other) construction techniques would affect my decision on whether to go 1 or 2" on the XPS.


Also, what is your overall R value goal (hell I don't even know what mine was)
If you're planning on interior batt insulation, you may be able to use R-11 with 1" XPS vs. using R-13 with 2" XPS and come out ahead. I never did the comparison myself.


Hope this helps somewhat.
 

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Discussion Starter · #13 ·
Save yourself some money and go with 1" XPS instead of 2". If you want to increase your R value then add some unfaced fluffy pink stuff between the studs.
 
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