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-   -   EPS or XPS (http://www.diychatroom.com/f19/eps-xps-128613/)

Jeff0101 01-03-2012 07:03 AM

EPS or XPS
 
Hello, any help here would be appreciated.

After much research, I installed 2" EPS foam board (Plastispan) on my poured basement walls. Now I only have to seal the seams. However, now I learn that EPS and XPS are different, and I am trying to determine if I should continue or rip and replace with XPS. As I now understand it, the moisture protection feature of EPS is not as great as XPS (contrary to previous advice I received). So do I now continue with wood studs, roxul (or fg) between studs, and then drywall, or do I rip it out, and install XPS, then build my walls.

Thanks.

Jeff

gwa 01-03-2012 06:45 PM

Quote:

Originally Posted by Jeff0101 (Post 810846)
Hello, any help here would be appreciated.

After much research, I installed 2" EPS foam board (Plastispan) on my poured basement walls. Now I only have to seal the seams. However, now I learn that EPS and XPS are different, and I am trying to determine if I should continue or rip and replace with XPS. As I now understand it, the moisture protection feature of EPS is not as great as XPS (contrary to previous advice I received). So do I now continue with wood studs, roxul (or fg) between studs, and then drywall, or do I rip it out, and install XPS, then build my walls.

Thanks.

Jeff

As you've learned, XPS and EPS are two different animals with very different characteristics. EPS readily absorbs water and will become saturated. XPS will NOT absorb any water. In my opinion, the EPS should be torn out and replaced. It might be possible to install a vapor barrier that is airtight, but it would take a great deal of care. Any condensation that forms in the wall or any leakage from outside will soak into the EPS.

XPS is installed as roof insulation in what's known as an IRMA or inverted roof membrane assembly. In this type of roof, the XPS is installed above the roof membrane, unprotected from rain and snow.

concretemasonry 01-03-2012 06:50 PM

EPS is great for meat trays at the local supermaket and that is about it.

Dick

Gary in WA 01-03-2012 11:27 PM

Only 2” of EPS, R-? where are you located?

The EPS needs to be twice as thick as the XPS, if subbing, 2nd paragraph above photo 4: http://www.buildingscience.com/docum...ts?full_view=1
They both hold moisture, one absorbs it slower than the other.

Gary

jklingel 01-04-2012 12:25 AM

I believe the absorbing problem of EPS has been solved, and is no longer an issue. Passivhaus folks use a foot or more of it under slabs, and when I emailed Ms Klingenberg (?) w/ this very question, she said "That is no longer thought to be true" (that EPS absorbs). I submerged a chunk of each in a plastic container on 1/25/11, and just took them out to compare them. Both float like a cork. When I spoke w/ a very knowledgeable super-insulated builder up here last year, he said "I switched to EPS under our slabs because I am so tired of pulling up wet XPS." The community education coordinator at Cold Climate Housing Research Center here in Frb said he thinks it is a Ford/Chevy argument, but it looks like most folks are switching to EPS. The density of the foam may have something to do w/ it. XPS goes as high as 100, and EPS to 60 psi (the last I checked). EPS is cheaper and more environmentally friendly, so I am using EPS in the new house. What I believe kills foam is getting wet and then going through freeze-thaw cycles. The water eventually gets "between the chunks" in the foam, freezes, and opens more channels. That is from a cat at our Cooperative Extension service, who warned me about buying "used roofing blue foam" for that reason. PS: The stuff I have submerged is in the "normal" range of 15-25 psi, both types. That is all I know about the issue.

Jeff0101 01-04-2012 07:15 AM

EPS or XPS
 
Thanks to everyone so far. To clarify, I live in Ontario in the Barrie area. I am using 2" of Plastispan HD EPS, which is a higher density of EPS. I"ll be speaking with the Plastifab (Manufacturer) technician today on this issue, so I'll post what I come back with. Their data sheets are on their web site.

Jeff

Jeff0101 01-04-2012 07:17 AM

By the way GBR. It is R8. Also what do you mean by "subbing"?

Gary in WA 01-04-2012 12:58 PM

Sorry, subbing or substituting.....

The foamboard needs to be thick enough to keep the interior side of foam from condensing warm basement air. To thin a foam in a cold climate (below ground frost line) would wet the cavity insulation due to dew point. Need more thickness of EPS vs. XPS to achieve enough R-value against dew point.

So these may no longer be true?
http://docs.google.com/viewer?a=v&q=...t5jlOsa_kZRRgw

http://docs.google.com/viewer?a=v&q=...z5KEzgJVBCTo-g

Find out if it is a Type 1, 2, 3, or 4 for the specific perm rating; http://www.nrc-cnrc.gc.ca/ccmc/registry/pdf/12425_e.pdf

The plastic facers may completely block the absorbing qualities you need, more research here is needed. You don't want any poly facing on the foamboard, either side........

Gary

Gary in WA 01-04-2012 01:14 PM

Compare your location annual heating degree days to the cities listed (HDD) for foamboard thickness or figure out the Delta-T for the dew point in your wall, pp.9; http://www.eere.energy.gov/buildings...s/db/35017.pdf

Page 10; http://www.buildingscience.com/docum...lation-systems

Delta-T: http://www.greenbuildingadvisor.com/...ally-necessary

And, welcome to the forums, gwa!

Gary

jklingel 01-04-2012 01:36 PM

[QUOTE=GBR in WA;812255]

So these may no longer be true?

[URL="http://docs.google.com/viewer?.....

Gary[/QUOTE]
I think the question is "Were they EVER true?" Man, I wish I knew w/ 100% conviction. Documents from DOW, or any business, are suspect. Nothing personal, DOW, but not all companies are 100% forthright and honest, and I really don't know about DOW. I like to think they are, but the old cliche "I was born at night, but not last night" comes to mind. I am going to do some more freeze/thaw testing, like I did last winter, but more controlled this time. I'll post what info I have several months from now. In the meantime, I'd like to hear any info from independent folks on this issue. I am slightly undecided, but surely leaning toward EPS (and keeping it as dry as possible).

Jeff0101 01-04-2012 02:09 PM

EPS or XPS
 
Well, here is more info:

The product is Type 2. I spoke to the manufaturer who suggests the following: their product against the cement wall, and don't seal the seams, but do seal the rim joists above. If then adding stud walls, insulate in between the studs with Roxul. Then put on vapour barrier (poly six), and dryall 1/2 inch.

My building department said the same: DO NOT SEAL THE SEAMS, if adding a stud wall filling with more insulation. DO then use a vapour barrier before the drywall. I need R13 on the walls (per my building dept), so I have to add insulation between the studs. Roxul is simply a better choice than fibreglass insulation in that arrangement.

Jeff

jklingel 01-04-2012 02:42 PM

They still recommend a vapor barrier in a BASEMENT? Hmmmm. I'd be careful with that one.

"Incorrect use of vapor barriers is leading to an increase in moisture related problems. Vapor barriers were originally intended to prevent assemblies from getting wet. However, they often prevent assemblies from drying. Vapor barriers installed on the interior of assemblies prevent assemblies from drying inward. This can be a problem in any air-conditioned enclosure. This can be a problem in any below grade space...."

From http://www.buildingscience.com/docum...r_code_changes

Jeff0101 01-04-2012 03:15 PM

EPS or XPS
 
Here in Canada, our federal housing corporation CMHC supports this assembly arrangment. All providing the seams to the foam board is NOT sealed.

Jeff

AGWhitehouse 01-04-2012 04:58 PM

I wouldn't recommend the vapor barrier on the inside face of a below-grade foundation wall either...CMHC supported or not...

Jeff0101 01-04-2012 05:08 PM

EPS or XPS
 
Just to be clear folks, the direction I've received is that the vapour barrier is to go on just before the drywall, and NOT against the cement wall (just in case someone thought otherwise). That being the case, I have to build per the building department in my town, and have no choice otherwise.

Jeff


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