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echonewyork 02-07-2013 01:38 PM

Rigid Foam Board
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

brockmiera 02-07-2013 01:50 PM

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

echonewyork 02-07-2013 05:04 PM

I believe they are both XPS

Trucon01 02-07-2013 05:06 PM

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

GBrackins 02-07-2013 07:01 PM

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

Gary in WA 02-07-2013 11:02 PM

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


echonewyork 02-08-2013 05:11 AM

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

VonTed 02-08-2013 07:27 AM

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.

echonewyork 02-08-2013 07:32 AM

Foamular OC 250. 2inch

echonewyork 02-08-2013 07:36 AM

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.

Gary in WA 02-10-2013 07:58 PM

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!


echonewyork 02-12-2013 07:22 AM

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

mikegp 02-12-2013 09:26 AM

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

brockmiera 02-12-2013 09:51 AM


Originally Posted by mikegp (Post 1115621)
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!

Gary in WA 02-12-2013 10:22 AM

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); under the overlap that can give-some with slight movement. The foam boards shrink over time (aging); Just like a rim joist, it's the air leak that will give up the moisture in condensation; 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;

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

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