I found a bit of info today that I thought I ought to share. There is actually a standard for EPS used in structural applications (like under a footer). The standard I usually see is ASTM C578, which specs “Type I”, “Type II”, etc. There’s a second standard, ASTM D6817, which gives a requirement for compressive resistance at 1% deformation, the maximum safe pressure for long term loads.

I found one manufacturer’s nice little cross reference between the standards at http://www.styrotech.com/downloads/EPS-DataSheet-ASTM-D6817.pdf

This document gives some background for why 1% is the safe compression: http://tstark.net/wp-content/uploads/2012/11/82c-Geofoam-BearingCapacity-BCR2A-2009.pdf

I would always consult an engineer before designing in structural foam, but I think this is useful knowledge for exploring new designs. It’s at least a better starting point than the not-very-useful 10% deformation pressures that have been thrown around.

–John