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XPS storage

I'm buying recycled 4" XPS to go under the slab for my new house in zone 6 Maine.
It wasn't as easy to find as I had expected, so when I found some, I ordered it. It gets delivered next week, but I probably won't need it for a few weeks or a month. Will it be OK to stack it on some framing lumber on the ground at the building site until I need it? I could throw a tarp over it if needed. I could put it in the barn, but then I'd need to move it again.

I assume a little moisture won't hurt, but I want to be sure.

Asked by stephen sheehy
Posted Aug 5, 2014 3:39 PM ET
Edited Aug 5, 2014 4:15 PM ET


9 Answers

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Throw a tarp over it. XPS can take on water if water is allowed to puddle on/under it, and takes quite awhile to dry out under a slab.

Polystyrene is also degraded by sunlight, but a month isn't going to make or break it.

Derate the performance to it's fully depleted R4.2/inch for performance estimation purposes. It may perform somewhat better than that for the first decade or two, but the R5/inch is the average performance over the first 20 years or so. As the blowing agents slowly outgas over time, XPS reaches the same R/inch of EPS of equal density.

Answered by Dana Dorsett
Posted Aug 5, 2014 4:05 PM ET


Dana, I have used XPS for 40 years. It can handle a month anywhere. I have scrap pieces that are outside for the last 10 years, and they could be used tomorrow.

All this talk of EPS, it should be noted that big box store EPS is not the EPS to use most of the time.

Dana, where do you buy EPS and what brand, and what type for where??? Be nice if you always noted more info about EPS every time you mention to use it. Someday I will look into sourcing it instead of XPS, you are slowly twisting my arm long distance....
;) aj

Answered by aj builder, Upstate NY Zone 6a
Posted Aug 6, 2014 10:48 AM ET


AJ and Dana,
is it a problem sourcing EPS down in the US of A,
i seen it mention a few times here already and i feel like it is much easier to find
XPS and ISO than EPS ..which is exactly " le contraire " from what we have here up.

Polyiso here is completely inexistant in most hardware store,
only the "roofers" and their supplier useit ,
and even there some of the big suppliers here are also producing EPS themselves for roofing purposes.

I can find any quantity or density required of EPS within 1-2 days within 2 hours of Montreal,
at very good prices ... but it is almost impossible to get high density XPS :p

What about moving XPS blowing to Co2 as in europe ?? is this going to happen anytime soon ?
( is it Co2 ..not sure )

As for the topic,

i have no real experience with XPS outside other than some parts we left behing a building for a decade or so ..and to the hand the pieces still feel acceptable for use

EPS other than it's sun degradation is pretty neutral when left outside..
It gathers pretty low moisture and water if in high enough density
and only the first mm or less feels degraded by the UV

Answered by Jin Kazama
Posted Aug 6, 2014 12:31 PM ET


I did the same thing as you - I ordered a pile of used XPS when the opportunity came up long before I actually needed it.
I stored it in my barn, but I have been storing the left-overs under a tarp.
Put something under it and throw a tarp over it and it'll be fine - biggest concern is probably the sun as Dana suggests.
Well, bears can sometimes be a problem too:

Answered by Lucas Durand - 7A
Posted Aug 6, 2014 2:28 PM ET


Jin: In the states even the big blue & orange box stores usually carry at least some amount of EPS (sometimes only Type-I goods with vinyl or foil facers) as well as foil-faced polyiso, along with a few thicknesses of 1.5lb XPS. Small and medium sized EPS fabricators exist in almost every US state, and it's commonly in stock at distributors that cater to the construction trades (rather than DIY home owners.) Regarding availability in Quebec, Atlas (one of the bigger manufacturers) has small-scale distributors catering to the residential market, found quickly in a web-search:


I have no hope for XPS being blown with CO2 in North America any time soon. It's a marketing issue: Why should I spend this much for the same R4/inch that I can get with EPS at a discount? If HFC134a becomes banned for that use (as it has in Europe), my guess is that manufacturers will switch over to HFO1234yf , which has similar characteristics (but a GWP of only ~4x CO2 ). There may be some reluctance to make that switch sooner, since HFO1234yf is flammable, and may require adjustments to other aspects of the manufacturing processes to make both the manufacturing and use safe enough.

Answered by Dana Dorsett
Posted Aug 6, 2014 3:06 PM ET


AJ: I'm not in the construction biz, and only occasionally in the market for EPS. But reclaimed & surplus EPS is always in stock (in volume!) at this place local to me:


For bigger volumes or custom shapes (tapered goods for flat-roofs, etc) these folks work:



(both are within 40 miles of me.)

These guys are national distributors of both EPS and Dow's XPS, and it looks like they have a distribution facility in both in Buffalo and Rochester/Syracuse, just eyeballing it from their li'l map:


Answered by Dana Dorsett
Posted Aug 6, 2014 3:39 PM ET


Dana ok ... weird that i remarked many comments here from USA folks having hard time to find EPS.
May be only in certain states?

Yes i've dealt with 2 of those manuf in the past,
there are also 2 or 3 other large EPS manufacturers within 2 hours from MTL .
So you see EPS everywere here,
and the most popular under cladding exterior insulation is a tyvek faced EPS

To be frank, i believe i have never see any new construction with EPS or ISO as exterior insulation locally.

But, XPS used to be the norm for foundation interior insulation, which is readily replaced by EPS also with new faced products.

Lot's of alum faced EPS is now used on the interior to do airsealing ( tuck taped ) and reach up to codes in new construction.

How is the pentane used for blowing up EPS as far as GWP ?

When they rate a certain GWP gaz used on a specific product, does it take in account the quantity used for every different and sub types of products ?

Surely the quantity differs with density and manuf methods.

Answered by Jin Kazama
Posted Aug 6, 2014 4:35 PM ET



this is by far the most common exterior insulation used recently around here.

But still i do not see that many building with exterior insulation ... most builders still use the interior
aka cheaper method as they save on the air sealing labor that way.
more $$$$ in the pokets :p

Answered by Jin Kazama
Posted Aug 6, 2014 4:38 PM ET


From the specs, I'd guess that the 1"-175" Iso-clad product with facers is Type-IX EPS, and at 2" and over it's Type-II EPS:


If it were XPS blown with HFCs it would all be ~R5/inch, not R4.2-R4.6

The global warming potential of pentane is about 7x CO2, which isn't a very severe hit.

The global warming potential of these gases is on a weight basis, and is typically listed at the 50 or 100 year impact potential. It is not related to how the material is being used. The R410a in your mini-splits has a GWP of about 2000x CO2 for a century, but when used in that application it doesn't (or at least shouldn't, if done correctly ) leak, and would not end up in the atmosphere. In a foam insulation product the blowing agent is guaranteed to leak most of it within the first 50 years, which is why it matters more, even at a somewhat lower absolute GWP.

Answered by Dana Dorsett
Posted Aug 7, 2014 4:36 PM ET

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