# EPS or XPS



## Jeff0101 (Jan 3, 2012)

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


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## gwa (Sep 17, 2010)

Jeff0101 said:


> 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.
> 
> ...


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.


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## concretemasonry (Oct 10, 2006)

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

Dick


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## Gary in WA (Mar 11, 2009)

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/documents/digests/bsd-103-understanding-basements?full_view=1
They both hold moisture, one absorbs it slower than the other.

Gary


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## jklingel (Dec 21, 2008)

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.


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## Jeff0101 (Jan 3, 2012)

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


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## Jeff0101 (Jan 3, 2012)

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


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## Gary in WA (Mar 11, 2009)

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=cache:M8LGdKfi1yMJ:www.dow.com/PublishedLiterature/dh_013e/0901b8038013ede3.pdf%3Ffilepath%3Dstyrofoam/pdfs/noreg/179-06011.pdf%26fromPage%3DGetDoc+permeability+ratings+of+sidings&hl=en&gl=us&pid=bl&srcid=ADGEESj2HlSU9SGLtx6MUOmbi_mJRuEufjmOjvbs-LJtrZ50rKT1Yqwgm3jPzvQt5dNG3lofjVwH_jVsuwCMAKQzEBcCPOlz7kpvTnXH5mfDcTRkUcHaW2aZAWJrAiBYUoXbY44FW&sig=AHIEtbT1X6_1p3ibUPYAt5jlOsa_kZRRgw

http://docs.google.com/viewer?a=v&q...lEbqKY&sig=AHIEtbQYwz6vG-jPF6_Uz5KEzgJVBCTo-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


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## Gary in WA (Mar 11, 2009)

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/building_america/pdfs/db/35017.pdf

Page 10; http://www.buildingscience.com/documents/reports/rr-0202-basement-insulation-systems

Delta-T: http://www.greenbuildingadvisor.com/blogs/dept/musings/are-dew-point-calculations-really-necessary

And, welcome to the forums, gwa!

Gary


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## jklingel (Dec 21, 2008)

GBR in WA said:


> So these may no longer be true?
> 
> [URL="http://docs.google.com/viewer?.....
> 
> Gary


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).


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## Jeff0101 (Jan 3, 2012)

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


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## jklingel (Dec 21, 2008)

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/docu...rs?topic=resources/vapor_barrier_code_changes


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## Jeff0101 (Jan 3, 2012)

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

Jeff


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## AGWhitehouse (Jul 1, 2011)

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


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## Jeff0101 (Jan 3, 2012)

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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## AGWhitehouse (Jul 1, 2011)

Jeff0101 said:


> Just to be clear folks, the direction I've received is that the vapour barrier is to go on just before the drywall


That's what we are cringing about...there are alot of studies and scientific evidence out there supporting that this is generally considered a bad idea when address below-grade concrete/masonry walls. Above grade is a whole different animal. But, if your local official has you hog tied, then I digress...


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## Gary in WA (Mar 11, 2009)

Page 59, #6.2- conclusions from an article dated ’07; ftp://ftp.cmhc-schl.gc.ca/chic-ccdh...ngual/Vapour_Permeance_Volume_1_Web_sept5.pdf

Check out- ‘Field study” pp. 2: http://docserver.nrca.net/pdfs/technical/317.pdf

A good read, especially “Conclusions” on pp.22; http://www.buildingscience.com/docu...ing-hygrothermal-modeling-basement-insulation

Jk, now they are messing with my mind………… check it out; http://www.buildingscience.com/docu...merica-high-r-foundations-case-study-analysis Notice the vapor barrier and foil-faced polyiso?


Kind of shoots the whole v.b. thing in the foot, at least for me......


Gary


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## jklingel (Dec 21, 2008)

Oh, sigh... Our city building dept still mandates visqueen above grade, much to the discomfort of a few knowledgeable builders. And then one of the local engineers claims that the HRV's are causing mold problems. Interesting. He may be right, but I can't buy it. Warn the local authorities, and in the event that you get mold/rot, sue 'em. You'll likely be OK with the visqueen, though, as it apparently is working in your environment.


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## jklingel (Dec 21, 2008)

Gary: Thanks for the links. I will try to get more "into" them soon. As for the Canadian one, I am confused. Here is what I have to say about what I've read so far, and it does not seem to, in general, necessarily support the use of visqueen, IMO. My comments and questions are after the bullets.


Pg 6, 2.2.2: Water penetration into a wall or solar heating of saturated absorptive cladding will 
increase the potential for mold growth on interior drywall finishes if the polyethylene is removed. Polyethylene has been found to protect interior drywall even where studs had rotted and corroded from water ingress. •• No kidding? Glad that sheet rock was protected! I’d hate to lose it when the house fell down. Sarcasm aside, I would wonder if the wall would maybe have dried out if the vb were not obstructing its movement.

a) Building Research Establishment, UK (1989) (As referenced in 2005 by 
Derome & Huang): It was stated that removing the vapour barrier should 
not be considered since summer condensation could occur behind low-permeability interior finishes. •• What am I missing here? So you want the vb to stop the water in the wall instead of at the “paint”. WTH? Again, why not let it through with low perm paint?

b).... and that the importance of proper vapour retarders as well as air barriers should not be underestimated. •• Key words; retarders, air barriers.

It is suggested that omitting polyethylene vapour barriers may result in increased condensation problems due to air leakage. This may be true unless the industry can rely on contractors to make other layers airtight. •• So, AIR seal. Duh!

e) ...where leakage led to... •• So stop the air leakage.

g) It is concluded that the internal wall must have sufficient vapour resistance to prevent 
condensation and reduce risks for mold growth. •• Vapor resistance prevents mold? WTH? Or maybe the wall was permeable enough to let the vapor out? This conclusion seems like it was not necessarily arrived at scientifically, or I am just confused.

Computer modeling predicts that the removal of the vapour barrier can significantly increase the moisture content of the interior gypsum board facing. •• Why is the water coming from the outside, and why is it not passing through? I’d sure like to know if there was a ventilated rain screen and WRB on these walls. Maybe that info is in the details, and I’ll try to read more later. For now, I quit and read the Conclusions.

Conclusions: This part struck me: 6.3, Further Work: This research suggests that interior vapour control at the lower portion of the basement wall is unnecessary or inhibits drying. Code officials should be informed about the results. Changes to codes and construction practice are likely. Permeability in the below-grade portion of the basement wall can be advantageous and should be explored further. 

I do not read this paper as doing much to support the use of visqueen below grade, and it leaves a lot of wiggle room for its use above grade. The references to “better air sealing” seemed to overshadow any benefit assumed to the visqueen. Further, I did not see where they demonstrated that “this well air sealed wall w/ visq outperformed this well air sealed wall w/out visq”. I think that anyone using this as a “proof” that visq is necessary, or even useful, is stretching their imagination. Sorry, but I just don’t see it, and I freely admit my bias to not liking visqueen, despite its apparently working in my own house (above grade). So, someone who is in favor of visqueen below grade read this and give us your interpretation. thanks. j


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## Jeff0101 (Jan 3, 2012)

One other small issue is that I have some odd angles in the basement corners, and in one corner the builder left a piece of wood, probably from the forms, embeded in the poured cement. No way I can extract it. Looks like a 1x3 or otherwise is just surface wood that stayed after the form was pulled off. I'm thinking I will just entomb it in. 

As for the EPS, I will stick with it. The topical range of answers on all the blogs and chat rooms is mind boggling, and although it provides deep understanding, does not eliminate the use of EPS, the type I am using, and in many knowlegable cases, supports the use of EPS. 

***Good vapour barriers, dry environment, low humidity control, great drainage outside, seem to be the overriding basics, and if they are all covered, you can use any of the consumer grade products if you construct approriately. Those are my conclusions, for what it's worth.

Jeff


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## jklingel (Dec 21, 2008)

It would be interesting to see why a vb is apparently mandated in Canada when the CHMC (CMHC? whatever) report concludes this "e) This research suggests that interior vapour control at the lower portion of 
the basement wall is unnecessary or inhibits drying", which seems in agreement with the BS report. Ask a local official, if you don't mind, and report to us. There must be other information they are using to make that decision. Thanks.


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## Jeff0101 (Jan 3, 2012)

Yes, I will have a long discussion with the inspector when he is here on site about all this. They typically get a lot of criticism, but I have found them actually to be well informed, at least the ones I have dealt with. I haven't always liked what they said, but I haven't been able to proove any of them wrong...in the past.

Jeff


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## jklingel (Dec 21, 2008)

Good to hear they are reasonable people, being in a position of authority. Let us know what "the rest of the story" is. Thanks. john


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## pete0403 (Dec 22, 2010)

Thanks for this thread...very interesting. I'm also in ON and it's good to see advice being thrown around for our climate instead of the southern parts of the US.

I always thought 2" of XPS against the slab taped and foamed tight was recommended. Then build the wall in the normal way with no VB. This allows the wall to dry to the inside. Is this not recommended practice anymore?


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## Jeff0101 (Jan 3, 2012)

I'd say the floor is a different matter. But on the walls: If you use XPS of at least 1.5" you can tape it and do away with the vapour barrier, depending on two things; what other additional insulation you may be using, and what your building dept says. It is the multiple insulation products which can cause some issue. If using EPS, don't seal the joins, and do use a vapour barrier. All that being said, your specific basement environment also maters. If you have water infiltration, don't build until you have it resolved. 

On the floor, I'll probably use Tyroc. Made in Canada from rubber and recycled plastic, indestructable from water, provides a thermal break, and is inorganic, which on a floor is Gold. Sold at Home Hardware stores. Both Barricade and Dricore have that sheet of OSB which is organic. It worries me. Tyroc, no worries. Tyrocinc.com.

Jeff


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## jklingel (Dec 21, 2008)

Pete: Have you done a heat loss analysis yet? That is #1 on the list. Depending on what your HDD (heating degree days) and local soil temps are, you may want to consider using a LOT more foam under your slab than 2". What is "recommended" is often tradition. Some folks up here still say 2" of foam is adequate, and I guess that depends on what "adequate" means to you. I will be using 10" under the slab, and 12" under and outside the footer (edge beam, whatever you want to call it). A very knowledgeable builder here is using 12" of eps and pouring an 8" slab on top of that, then building. Ten to twelve inches may be excessive for you, but I imagine 2" is a bare minimum (ie, code). Just a thought, but a slab is cold 365 days/year, whereas a wall gets heated part of the time. Lots of energy goes out through a slab if it is not slowed down. Just a thought.


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## pete0403 (Dec 22, 2010)

I was talking about inside between the poured wall and the studs. Maybe I misread everything in this thread nline2long::shutup::blush:


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## jklingel (Dec 21, 2008)

pete: you're good. i misinterpreted what you said. sorry about that. it still may be worth looking at 4" inside.


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## Gary in WA (Mar 11, 2009)

So, it appears none of you have looked at or read about what is behind door #3, 4, or 5? From the last one I sited...... Plastic inside, foil-faced foam inside.....

Gary


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## jklingel (Dec 21, 2008)

Gary: I looked at options 3, 4 and 5; increasing order of "good". I saw what I saw in the Canadian study, but maybe I read too fast (or don't retain much....). Poly is not such a good idea, for one. What were you seeing in all this?


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## Gary in WA (Mar 11, 2009)

I was surprised to see foil-faced polyiso after the 2" of XPS in the wall, acceptable to BSC after all the studies against in below grade. Other articles of theirs use polyiso below grade when leaving it exposed (without drywall) and change it out before drywall.... The dew point is safe because of so much foamboard that the amount of interior diffusion from the basement is a mute point and the concrete will never get basement air to it.

Gary


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## jklingel (Dec 21, 2008)

ok. got it. john


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## Perry525 (Jan 10, 2010)

There are two sides to this story, one water making its way through the walls and floor, result a damp surface and water vapor made in the home and condensing on a cold wall or floor.
With the outside water making the surface damp, then exposure to warm air will keep this under control.
With water vapor in the air, then you can either keep the wall surface temperature above dew point, or use a water vapor proof plastic sheet backed by polystyrene to keep the water vapor away from the wall.
The water vapor proof plastic sheet, will fail if the insulation behind it is so thin that the surface temperature is below dew point and condensation will form on the plastic. If the plastic sheet, is not perfectly water vapor tight, due to poor installation, and the insulation doesn't keep the suface warm enough then the water vapor will pass through the plastic and condense on the cold wall/floor.
It is very difficault to fit a water vapor proof sheet over a wall or floor and to get it to work as intended, as the water vapor molecules are very small and they can pass through many things always attracted towards a cold area or surface.
Keeping things warm and avoiding condensation by letting convected warm air flow over them is much easier.
Think of a typical window during the winter.....during the day with warm air flowing, the window stays clear. Close the blinds or curtains at night and the space behind losses its warm air circulation, temperature falls and condensation forms.


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