# Rigid Foam Board



## echonewyork (Feb 7, 2013)

I plan on putting rigid foam on basement walls. Live in NJ. Any difference between Owens Corn Foamular vs Dow Styrofoam? Plan on using 2inch. Only difference I see is price and color and brand. Anything I am missing? Thanks


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## brockmiera (Oct 9, 2012)

Are they both XPS? The Dow I've seen at HD is EPS and has a lower installed R value.


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## echonewyork (Feb 7, 2013)

I believe they are both XPS


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## Trucon01 (Jan 10, 2012)

Around here, HD carries the pink Owens Corning and Lowes carries the light green Dow XPS. If both are XPS, both should be rated the same 

1" = R5
2" = R10


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## GBrackins (Apr 26, 2012)

for your reading pleasure ..... I myself prefer the Dow, but do your homework do you know what's what

http://building.dow.com/na/en/products/insulation/rigidfoam.htm
http://msdssearch.dow.com/Published...foam/pdfs/noreg/179-07873.pdf&fromPage=GetDoc

http://building.dow.com/na/en/products/insulation/rigidfoam.htm


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## Gary in WA (Mar 11, 2009)

One absorbs 3 times water, what type of OC? One retains 96% R-value, another 98%..

Gary


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## echonewyork (Feb 7, 2013)

Which absorbs more? DOW? Which do you recommend Gary? Whats OC? Sorry, got a newbie here. Learning day by day


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## VonTed (Feb 6, 2013)

OC = Owens Corning I believe.

Trying to figure out the shorthand here on these forums can be challenging! 


PS. Don't take my guess as gospel---- it is my guess.


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## echonewyork (Feb 7, 2013)

Foamular OC 250. 2inch


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## echonewyork (Feb 7, 2013)

Its either OC foamular 250 2in or Dow Styrofoam square 2in. OC for $37 per 4x8 and Dow for $50 4x8. Dont mind the price diff if im getting a better product.


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## Gary in WA (Mar 11, 2009)

For that big of a price difference, figure them equal. The water absorption test is less with OCorn. = 0.10 and Dow= 0.30... not a biggie considering water vapor will keep the board saturated most the year anyway, lol. They used to be the same company till one branched off. Be sure to use a closed grid glue pattern on the concrete, to reduce any air leaks inadvertently made when installing it. Add some 1/2" EXP under the frame wall bottom plate for a thermal/air/capillary break. Air-seal the rim joists with canned foam using extra 2". Use a latex based paint on the drywall. Pictures when done... we love pictures!

Gary


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## echonewyork (Feb 7, 2013)

Any tape to seal the foamboard edges to each other or tongue and groove enough? By the way, Gary, your posts are simply great.


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## mikegp (Jul 17, 2011)

I use Tyvek tape. About $11 a roll at HD. You definitely want to seal the seams.


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## brockmiera (Oct 9, 2012)

mikegp said:


> I use Tyvek tape. About $11 a roll at HD. You definitely want to seal the seams.


+1 for Tyvek tape. That stuff is awesome!


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## Gary in WA (Mar 11, 2009)

I'd use canned foam or furnace duct mastic/mesh tape for total air-seal. The c. foam is more flexible, or use some quality caulking or better still; acoustical sealant (best); http://www.liquidnails.com/products/acoustical-sealant-AS825 under the overlap that can give-some with slight movement. The foam boards shrink over time (aging); http://www.buildingscience.com/documents/published-articles/pa-foam-shrinks Just like a rim joist, it's the air leak that will give up the moisture in condensation; http://www.buildingscience.com/docu...joist/files/bscinfo_408_critical_seal_rev.pdf Of coarse on a wall, the air is going from inside to wall, not both ways as in rim. ADA the drywall to stop air at the first line of defense; http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/

Gary
PS. after that, I just HAD to use more links, lol.


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