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Community and Q&A

Is non-rated EPS worth using?

Darren Williams | Posted in Energy Efficiency and Durability on

I have a free source of EPS foam used in packing. The sheets are 12-16in. W x 4-8ft L x 1/2-3/4in thick. They are rather soft and compress easy but when stacked to say 2 in thick they feel more usable.

I was thinking of gluing them into boxes to air seal around electric boxes and such and baffles at the eaves, My house was on a wet dirt crawl space so I dug it out to about 7ft, as far as i could go before hitting too much granite( northern NH) and sat it on an ICF foundation, can I use them on the outside to insulate the footings?

Also the basement floor is compacted sand and stone mix, 2 layers of 6mil poly sheeting,2in of XPS foam and 2in of concrete. The foam is even with the top of the footings and the concrete on top, this was done to save headroom, but I find condensation forming at the edges near the walls where there is no foam, not a big deal but I want to finish off one section as a playroom for the kids.

Was planning on using a cheap moisture resistant click type vinyl flooring. Do you think 1/2 or 3/4 inches of the EPS under the floor would be a bad or good idea? I saved a few hundred pieces of this stuff and can get 4-8 more per week, so what do think? use it or chuck it? thanks for the help.

Darren Williams

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  1. Rick Evans | | #1


    Are the EPS beads large or small? The larger ones are typically from recycled EPS rather than virgin EPS. The compression strength of these are really low and probably not suitable under any flooring. (although a couple of little kids might not mind)

    Consider cutting and stacking the EPS to make a 1 foot cube. Then place it on a postal scale. If it weighs .90 to 1 pound then it is Type I EPS. 1.35 pounds to 1.5 pounds would mean it is Type II. These have compression strengths @ 10% deformation of 10 and 15 psi, respectively. People put Type II under slabs all the time. Type I would probably work too unless you are parking cars on it.

    Whatever the stuff is- I can't imagine that it would hurt scattering it around a footing for frost protection or using as part of a ground gutter system.

  2. User avatar GBA Editor
    Martin Holladay | | #2

    Rick's advice makes sense. If I were you, I might use this foam for some purposes, but probably not under flooring. The amount of money you will save isn't worth the hassle you would suffer if you have to pull of the floor and re-do the job in the future.

  3. Darren Williams | | #3

    Thanks for the input, looks like I will use it on the footings but not under the floor. On the floor issue, if I used 1/2 or 3/4 in of xps or 2lb eps do you think this would be enough to control the condensation?

  4. User avatar Expert Member
    Dana Dorsett | | #4

    Most packing EPS is VERY low density, (half pound per cubic foot or so) designed to absorb impact forces with an R value of R3-R3.5 per inch. Some people use crushed/crumbled/ground up packing EPS and stray bead scrap as an insulating aggregate for non structural concrete (for modeling or insulative coating) that delivers on the order of R1.5-R2/inch. It's pretty brittle stuff, not particularly "walkable" but can be made to look like solid concrete items for uses in movie & stage props, etc, or outdoor yard ornaments, etc.

    Putting it under flooring (or even slabs) isn't likely to work very well.

    The amount of R value necessary for condensation control has lots of construction detail variables. (Sketch a picture of where you intend to use the foam and post it.)

    In most residential applications 2lb EPS (Type IX) isn't really necessary (unless specified by an engineer under footings, etc.) . Even 1.25lb density (Type VIII) commonly used for roofing insulation on large flat commercial building roofs is good enough for sub-slab foam in basements, etc.

    There is no long term thermal advantage to XPS over EPS. Over the 50+ year lifecycle of a building the (climate damaging) HFC blowing agents that give it the performance boost suitable for labeling purposes diffuse out, and performance drop to about that of EPS of similar density (~R4.2/inch for 1.5lb goods). The "lifetime warranty" on XPS performance is only for R4.5/inch, but with so many other caveats they are pretty unlikely to never pay a warranty claim. Real world performance can cross that threshold in 20 years or less.

  5. User avatar
    Jon R | | #5

    Performance drops, but over a complete 50 year life XPS will use significantly less energy than EPS (ie, EPS can never catch up). But don't take this as encouragement to use XPS.

  6. User avatar Expert Member
    Dana Dorsett | | #6

    At the same labeled R value and foam density EPS is usually ~20% cheaper than XPS per R, but also ~20% thicker.

    But at any R value EPS is more more than 1000% greener than XPS from a total lifecycle environmental impact point of view. From that perspective the temporary thermal enhancement of XPS will never come close even assuming a 1000 year lifecycle.

    In Europe Type II XPS blown with low-impact CO2 has the same R-value as Type II EPS of equal thickness (but a lower vapor permeance and higher price.) All XPS in the US is blown with HFCs.

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