Q. In a SIP, how secure is the bond between the OSB skin and the EPS (expanded polystyrene) core? Can this bond be compromised by water infiltration or insect damage, or could the insulated core deteriorate over time? If that bond were to fail, it seems to me the whole structure would fall apart like a giant house of cards.
A. Gary Pugh, of Alternative Building Concepts, a Santa Rosa, Calif., green building company that specializes in SIPs construction, responds: EPS — a closed-cell, foamed plastic insulation with a 30-year track record — is inert to a wide range of chemicals, will not rot, has no food value, and will not attract insects, parasites, or any animal or plant life.
It's also nonhygroscopic, which means it does not readily absorb moisture, and its compressive strength and thermal properties are minimally affected by the small amounts (typically less than 0.2 percent by weight) of moisture it can absorb, and by temperature cycling.
EPS insulation is manufactured to meet the standards of ASTM C578, with ongoing compliance with this standard addressed through a third-party certification program.
In addition, the adhesives used to laminate wood facers to EPS insulation have to meet minimum performance standards established by the major codes with regard to exposure to moisture, temperature, aging, oxidation, mold growth, and compatibility with the EPS insulation core.
Reputable manufacturers of SIPs use adhesives that are in compliance with ICC Evaluation Service acceptance criteria AC05.
If a SIPs house can be picked up whole by a tornado, dropped a few feet away, then get lifted up by a pair of cranes and set down on a new foundation with little or no damage to the structure — which I've seen documented — I'm pretty confident that these panels won't delaminate.