Posted on June 8, 2015 by Scott Gibson
About to start a new house in Climate Zone 5, Nicholas C is working out the details of how to insulate the basement slab and foundation walls. There is more than one type of rigid foam insulation he could use, and it could be applied on either the inside or outside of the foundation.
For a couple of reasons, he's planning on 2 inches of extruded polystyrene (XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.) beneath the slab rather than expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.). The XPS would perform better in a wet environment, Nicholas says, and Owens-Corning, one insulation manufacturer, claims it no longer uses a "bad" blowing agent.