EPS versus XPS - Expert Opinions

[Crazy68Dart]

Hey all. I spent the better part of the weekend researching this topic. I am ramping up for a build and would like to put PEX in the slab. I may not use it immediately, but it will allow me to go that route if I decide to in the future for heating.

My concern is over which type of 2" insulation board to use. EPS or XPS. I have searched the forum and internet, and it seems like the general consensus is that XPS is "better". It is certainly more expensive.

However, I read many accounts where type II EPS is "better" long term with R value performance. It is also lower cost, which is all good, but I am not after the cheapest alternative. I want to use what is going to last and perform.

This is a one time deal. I don't plan on ripping up a slab in 10-20 years because the the insulation performance is an issue. I would hate to invest all the money for the radiant heating system to at some point in the future have to shut it down because it becomes too expensive to use (i.e. insulation properties dimish and heat loss occurs). The hydronic setup is certainly more expensive and more complex to install, setup, and maintain than a simple forced air system (my last garage use a forced air electric heater).

Thanks as always for the help.

 

[sands35]

XPS can be walked on. EPS will deteriorate rather quickly during the install.

Some of the insulating properties of the floor is due to the capillary break (i.e., stone) under the floor and how the edges are dressed. Which has very little to do with the foam used.

I am very happy with the infloor heat in my garage. A good bit of the perceived benefit is that the slab is around 5* warmer than the air - so my feet are warm. It also recovers very fast after opening the car door.

 

[anthony666]

i can tell from your post your miles ahead of the game because it seems you're willing to go the extra mile and get it done right

ground water is your biggest enemy when it comes to the slab .. i like to see a taped vapor barrier below the insulation to keep water as far away from the pex as humanly possible .. all the insulation in the world won't amount to a hill of beans if ground water can get up between the insulation panels and wick the heat from the bottom of your slab

 

[Highbeam]

Use the EPS, it is much cheaper and there are no drawbacks. The EPS can certainly be walked on. It is easier to break up if some idiot is sitting there and scratching it with a clawhammer but XPS can also be damaged if you are careless.

We use EPS for fill under roads now too. It is strong enough for bulldozers to track on and will not fall apart.

Most of the large warehouse roofs use EPS too. I've been to the factory, seen how they make it. You can buy 15 psi EPS or 25 psi EPS. Most XPS is 25 psi.

The real question is, why would you pay extra for XPS?

 

[JACDes]

[QUOTE

The real question is, why would you pay extra for XPS?[/QUOTE]


Per inch thickness XPS has higher R value.

2" EPS R=7.8

2" XPS R=10

Depending on the intended application it makes a difference.


If you use 1" or thicker XPS you do not need a vapor barrier. provide you tape the seams.

XPS comes is also available up to 45 PSI compressive strength.

if you need more R value EPS and XPS are no match for Polyiso.

 

[Crazy68Dart]

Not to knock any of the comments but:

- Iso is not suitable for underslab/on grade installations. So, not interested in debating its use for this purpose. But you are correct in that it has a higher insulating factor.
- 15 psi is more than enough for typical residential loads. More is fine, it will just be more painful to your pocket book.

 

[Crazy68Dart]

666, thanks. I just want to do it once.

Highbeam, thanks for the info. That is what I found as well. One thing, where does a DIYer find the proper type 2 EPS? Stuff at Lowes/HD/Menards does not seem to be type two but rather type 1. I was going to check with my contractor to see if he can source it.

My install plan is (bottom to top):

- Garage is footer/block foundation. 2" board along inside up to slab. Not sure if I am going to bevel the edge of board at top yet or not. Worried about the thinner concrete cracking over time. Not sure if it is advisable to somehow do vapor barrier at the wall or not. Struggling with how that would be beneficial.
- Use proper substrate, compact properly, etc.
- 10 mil vapor barrier, edges brought to surface/top of slab, taped seams.
- 2" insulation board, taped seams.
- PEX directly to board and mesh panels on top, or PEX to wire mesh and wire mesh on stands. Really concerned about nicking the PEX when saw cutting, so we'll see.

Thanks again all.

 

[joe--h]

R-control is what I've used. I bBought it directly from the factory. They are around the country, maybe near you. http://www.r-control.com/sitemap/ I can't find just foam on the site but they make it and sell it.
It's treated with borate so ants don't chew it. I bought a truckload, you probably don't need that much.

They make it in blocks and slice to thickness, so you can (or could) get what you want. Type II is plenty, 2100 pounds per square foot will hold up anything you're going to put in your garage.
Joe H

 

[Highbeam]

666, thanks. I just want to do it once.

Highbeam, thanks for the info. That is what I found as well. One thing, where does a DIYer find the proper type 2 EPS? Stuff at Lowes/HD/Menards does not seem to be type two but rather type 1. I was going to check with my contractor to see if he can source it.

My install plan is (bottom to top):

- Garage is footer/block foundation. 2" board along inside up to slab. Not sure if I am going to bevel the edge of board at top yet or not. Worried about the thinner concrete cracking over time. Not sure if it is advisable to somehow do vapor barrier at the wall or not. Struggling with how that would be beneficial.
- Use proper substrate, compact properly, etc.
- 10 mil vapor barrier, edges brought to surface/top of slab, taped seams.
- 2" insulation board, taped seams.
- PEX directly to board and mesh panels on top, or PEX to wire mesh and wire mesh on stands. Really concerned about nicking the PEX when saw cutting, so we'll see.

Thanks again all.

I purchased directly from the factory. I chose the 25 psi EPS with no attached plastic or foil barrier which was an option. I know a guy.

On top of the foam I placed mesh and then zip tied the pex to the mesh. The concrete guys tried to lift the mesh up as they poured but really, it is likely mostly on the foam. 5" of concrete and I cut 1" deep sawcuts in the slab with no worry at all about hitting the pex way down there.

EPS is made for underslabs. It doesn't hold water, water will drain back out of it as soon as you give it a way to go.

The R-value per inch is not known like it is with XPS. They are slippery about that. I think it depends on the density and the application but you won't see R anything stamped on the foam at home depot. I am happy with R7.8 but I suspect that the truth is closer to the R10 of XPS.

We rolled wheelbarrows and drug concrete pumper hoses all over that EPS and it held up great. It is slightly softer than XPS but who cares?

 

[Crazy68Dart]

I've only just started going through the huge radiant floor thread. What have you guys done with the top of the insulation around the foundation?

Cutting a bevel seems like a good approach, but looking for some ideas. Anyone actually just run it up to the squared off insulation board (yes, it would be visible, but who cares)? I worry a little about cracking if the concrete gets to thin around the edges.

Thanks!

 

[jvitez]

Plastispan makes a high density EPS suitable for in-floor radiant heat, R4.04 per inch, so 3" board would be ideal for a cold climate.

http://www.plastifab.com/products/insulation/plastispan-hd hydronic.html

http://www.plastifab.com/technical-library/design-manual/0406_Radiant Floor.pdf

About the foundation insulation: I know what you mean. I've read posts where guys have beveled the edge, but I too wonder if the concrete won't just flake away over time. I don't know if anyone ever tried this, but how about using construction adhesive to glue pressure treated 2x4's on the flat covering the insulation?

 

[Crazy68Dart]

Plastispan makes a high density EPS suitable for in-floor radiant heat, R4.04 per inch, so 3" board would be ideal for a cold climate.

http://www.plastifab.com/products/insulation/plastispan-hd hydronic.html

http://www.plastifab.com/technical-library/design-manual/0406_Radiant Floor.pdf

About the foundation insulation: I know what you mean. I've read posts where guys have beveled the edge, but I too wonder if the concrete won't just flake away over time. I don't know if anyone ever tried this, but how about using construction adhesive to glue pressure treated 2x4's on the flat covering the insulation?

Sorta what I was thinking, so you would have a 2x4 visible "border" around the slab I assume is what you mean.

Thanks for the links!

 

[Highbeam]

I've only just started going through the huge radiant floor thread. What have you guys done with the top of the insulation around the foundation?

Cutting a bevel seems like a good approach, but looking for some ideas. Anyone actually just run it up to the squared off insulation board (yes, it would be visible, but who cares)? I worry a little about cracking if the concrete gets to thin around the edges.

Thanks!

I used 2" xps around the edge, vertical. It's easier to work with and the solidness is helpful. I nailed it to my mudgirt which is permanent and the top of the mudgirt is even with the top of my slab. In areas where there was a mandoor or overhead door I cut the xps at a 45 so that the concrete would stay pretty, other places I left it square. Most of the time the concrete cream hides the xps, but in other places (non beveled) the thin cream popped off to show the foam.

The foam acts like a formboard. If you look close at the pex photo you can see the vertical xps.

 

[Crazy68Dart]

Thanks. Since you did a pole building, how deep did you go? I am planning to take the perimeter board the whole way down to the footer.

 

[Concrete Homes]

In our area, we do quite a bit of EZFloor-it is out of Wisconsin. It is EPS insulation and vapor barrier in one sheet. You can drive a laser screed over it. Holds the tubes, so no need for wire, chairs, etc. I think the website is EZFloor.com or something like that. I am in the Ready Mix industry, so we do a lot of shop floors, commercial slabs, etc.

 

[kj_mustang]

You can buy EPS in higher density but good luck finding it. I got a quote from a EPS manufacturing company that will sell to the public for higher density EPS and it was as much as the XPS from Home Depot. So I bought the 15 psi XPS and it held up fine to walking on it while I laid the pex and wire out.
In a pole building, if you are going to finish the inside of your walls, then there is no reason to bevel the top of the foam that is attached to the skirt/grade board. It will be hidden in the wall.

 

[ADSR]

I leveled my fill perfectly, walking and rolling a wheel barrel full on concrete on the ESP was no problem. I paid 14 bucks a sheet for 4x8/R7.5. The XPS was 40$ a sheet for R-10.

Not worth the extra price!!!

 

[bigman68]

Use this:

http://www.cellofoam.com/BuildingProducts/permabg.html

Much less expensive and works great. Contact Cellofoam for a local distributor.

 

[Crazy68Dart]

My garage will be footer/block foundation down to the frost line.

Yeah, challenge for me as been finding high density EPS.

Thanks for the replies. I'll check out some of the links you guys added.

 

[BadgerBoilerMN]

The cost of the equivalent EPS and XPS is often the same.

Density is the first specification. 15 or 25 psi is common for residential work.
Second is the R-value. XPS has a higher R-value at the same thickness.
Third is the over-stated hydrophobic qualities of EPS.

Finally, the debate is like that of PEX tubing. Since almost all of the PEX tubing available today exceeds the requirements of most of the radiant systems installed by a factor of 10 or more, fighting about which PEX is better wastes valuable time and sometimes convinces the simple minded that none of them are good enough!

Once you heat the slab, you will not have excessive moisture in the slab or the insulation below unless you have high ground water (rare).

As for the stack-up. I will beg to differ with my esteemed colleague High.

Here in Minneapolis we use a 6 mil vapor barrier, 2" of 250 XPS, staple barrier PEX to the insulation and lay 6-6-10-10 over all. with a 4" slab.

This is the specification for our heated driveways and from much experience with other theories we stay with this simple formula even in a basement remodel, sans the wire on occasion.

The reasons are simple and straight forward.

Though we often use enough rigid insulation to buy LTL and store it at significant savings we can get it at the big box any day and put it down the next. We know it will stand up to reasonable foot traffic. We know it will not retain significant moisture. We know it is more than adequate for structural loads and downward thermal flux.

We put the vapor barrier below the XPS because is practical and makes for good concrete. We put the wire over all because stapling is 4 times faster than wire ties and

Wire at the bottom of the slab serves no purpose since it must be enveloped by the concrete to add strength, (pulling doesn't work and can expose PEX to the saw) chairs slow the process and are hazardous to work around.

The PEX doesn't care where it is. You will not know the difference be it at the bottom or two inches from the top.

We also use 5000 PSI low-moisture concrete with fiber. This is the place to spend your money.

 

[Chris705]

Crazy68 - On my garage I was lucky and found 2'x4'x3" xps from a demo contractor advertising on Craigs List List for $3 a board - so I highly recommend looking on line for deals like that. It was dirty but I ended up doing both my foundation walls to footing and under the entire slab for cheap. If I didn't get that deal I would have used the EPS without any concern. At the edges I did bevel the insulation at a 45 degree cut and while my slab has only been down for a couple months I figure I won't be placing heavy loads right at the very edge (I did not place foam at the OH doors yet but will when I pour my aprons - I plan on putting a metal plate to span it there). My pex was zip tied to 6x6 wwm and stays right on the insulation, I used a 4000psi mix with mico fibers, air entrained for freeze thaw. Also did the 1" saw cut. Now saving for spray foam and then a boiler....it come eventually. Good Luck with your project!!

 

[Highbeam]

I agree with Badger, I think the only thing he was proposing that differed from my layout is the pex below the mesh and stapled vs. what I did which was pex on top of the mesh and ziptied.

I agree that the mesh is better laying on top of the pex but I did not have access to a stapler. The big bag of zip ties was available same day.It was also nice to use the mesh as a layout grid.

 

[BadgerBoilerMN]

When opportunity knocks...

I don't mean to pick.

 

[kj_mustang]

OR like I did, rolled out one row of wire mesh and ran the pex under that section of wire in the proper layout, repeat with each row of wire. Then wire tied the pex to wire after making sure the layout was correct. I then lifted the wire and pex off the foam. Yes, it is time consuming. Several ways to do this job.