Move Over, Foam: Sub-Slab Mineral Wool Is Here

Readers of EBN are well aware of our concerns with extruded polystyrene (XPS). The green building community has three concerns about XPS: first is the HFC (hydrofluorocarbon) blowing agent, which is a highly potent greenhouse gas; second is the brominated flame retardant HBCD, which is now on the Stockholm Convention list of Persistent Organic Pollutants and slated for international phase-out; and third is its styrene chemistry, which raises health and environmental concerns at various points in its life cycle (see Polystyrene Insulation: Does it Belong in a Green Building?).

But there have been frustratingly few alternatives for below-grade and (especially) sub-slab insulation applications. Polyisocyanurate risks moisture absorption; Foamglas is expensive and time-consuming to work with; and spray polyurethane foam (SPF) is challenging to install in this application and also prone to moisture.