Void Former Replacement

Foamglas or recycled glass fill/aggregate like Glavel or Aero may be an option. See this great BuildingGreen article: https://www.buildinggreen.com/product-review/new-foam-free-sub-slab-insulation (Thanks BG!) Dan Piselli, AIA, LEED AP, CPHD Director of Sustainability, Senior Associate FXCollaborative Architects LLP D +1 646 292 8137 | T +1 212 627 1700

My understanding is EPS is the standard material for fill applications. Generally less expensive than XPS, and available in custom thicknesses. Not quite as high in terms of compressive strength but close. But this may be a regional solution. XPS now sold in WA State and CA is required to be from low-GWP blowing agents and there are now products specifically made for these markets so the embodied carbon story has changed, at least in some locations. Not that I recommend either of these as the right solution. Jim Jim Hanford, AIA, LEED AP BD+C, Principal The Miller Hull Partnership, LLP

Owens Corning now makes a NGX substitute for XPS which has a 90% GWP reduction in blowing agents.  This recent CLF post found a 83% overall GWP reduction but an increase in eutrophication.  It is also made with 100% renewable electricity  https://community.carbonleadershipforum.org/t/epd-optimization-summary-published-for-owens-corning-foamular-r-ngx-xps-insulation/2712   You might be need to sign up for CLF to view it.   Here is OC's NGX product for engineered applications:  FOAMULAR® & FOAMULAR® NGX™ 400/600/1000 | Owens Corning Insulation   We found that the R-10 NGX product for thermal application runs about 22% higher than XPS based on recent contractor pricing (Just under $35 per 4x8 sheet versus $27).  FoamGlas pricing for the same R-10 value was 8 times that of XPS.   David C. Winans  AIA, NCARB, LEED AP BD+C & Homes
Senior Associate
GGLO
 

A bit more clarification is needed on pricing info provided yesterday:  All pricing is within the last month for the Seattle area.  You obviously need to verify pricing for your project's market.  The FoamGlas cost was for FoamGlas One (Owens Corning's Industrial product) or FoamGlas T4 in a 3" thickness to achieve R-10.  These products have compressive strenghths in the mid 80's to 100 psi respectively and are suited for structural applications.  The prices for XPS and NGX were for the lighter 25 psi thermal product more typical of a continuous insulation application.  The FoamGlas rep we spoke with said that the NGX 1000 product with a compressive strength of 100 psi will be closer in cost to FoamGlas, but still less.   FoamGlas T4 & NGX 1000 will definitely be higher cost than EPS.  If you want to dive deeper into appropriate applications & cost of Foamglass, contact Vishnu Vicknenthiran at Vishnu.Vicknenthiran@owenscorning.com or (929) 339-5211