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Re: GBlist: Recycled XPS
As I recall, the ASTM C 578 standard for EPS boards defines Types I through
IX, with the basic difference being density. A Type I board is 0.9
lbs./cu.ft., a Type II is 1.35 lbs./cu.ft., and so on. As the density
increases, so does the R-value. Type I is R-3.6 per inch at 75F, and Type
II is 4.0 per inch. More density also improves the compressive strength and
bearing ability. Type I is 1440 lbs./sq.ft. and Type II is 1872
lbs./sq.ft., which makes it suitable under slabs (by our code anyway).
Years ago, when EPS was a generic product, the boards weren't stamped and
we couldn't use them in construction because we couldn't show that they met
code. Today the (reputable) manufacturers of EPS stamp the boards with
these ratings and ensure they are meeting ASTM test standards. You can
still find un-stamped EPS boards at home improvement stores.
There was once a concern that in below-grade applications, moisture might
penetrate the bead structure, freeze, expand, and bust out the boards.
However, Western Insulfoam gave me a summary of a research report saying
that Twin City Testing Laboratory in St. Paul buried EPS boards along a
foundation and dug them up each year for three years, finding only a slight
loss of R-value. A similar study was carried out by Minnesota Department of
Public Service on EPS used on houses. In any case, EPS under a slab should
not be exposed to freezing conditions.
O'Brien & Associates
Environmental Building Consultants
Portland General Electric Earth Smart program
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