XPS outgassing?
dowens825
| Posted in General Questions on
Saw some used Dow Grayboard advertised as R5/inch and 25psi, which might work well for my basement floor retrofit (zone 5). The R-value is printed on the product, but I wasn’t able to find anything on the compressive strength other than a vague reference to a possible value of 15psi. While researching though, I saw some references to long-term outgassing of XPS, as opposed to EPS which apparently outgasses very quickly.
Is used XPS a safe choice for an inside basement insulation project in a real tight house or does the outgassing negatively affect air quality? Any way to verify the compressive strength of Dow Grayboard?
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Replies
Dave,
XPS does not outgas any substances that (at the level of outgassing that occurs) might affect human health.
The concern is with the atmosphere, and the extent to which the released blowing agents contribute to global warming.
There are no human health concerns when installing XPS in a basement, but most building codes require that XPS be covered with 1/2-inch drywall for fire safety reasons. Properly installed, this layer of drywall is an air barrier, which might help alleviate your (mostly unjustified) concerns about health effects.
Like the health aspects of outgassing you really don't need to be concerned about the compressive strength of any polystyrene insulation (EPS or XPS) that has a nominal density of 1lb per cubic floor or higher in this application. With even a half-inch plywood or OSB subfloor over it the dynamic loads aren't high enough to cause permanent deformation of the foam.
It's common to put hot electric water heaters directly on top of 1.5lb density EPS pads in some regions as a capillary & thermal break between the water heater & garage slab. Under a 4" slab you could park your Caterpillar D9 on top of 1.5lb EPS without breaking the slab. For a residential floor you don't even need 10psi (144 lbs per square foot) ratings on the foam.