Two companies in the Northeast are seeking to expand the market for a lightweight, insulating fill made from recycled glass that can take the place of stone aggregate in several residential applications, including subslab fill. AeroAggregates of Eddystone, Pennsylvania, announced this week it has opened a second kiln as it increases production of the foamed glass aggregate it now sells in parts of the Northeast. The material is made of post-consumer recycled glass and a foaming agent and, according to the manufacturer, can act as both a drainage and insulating layer. In Vermont, Burlington-based Glavel is currently importing foamed glass from a German manufacturer but plans to open a 12,000-square-foot plant in St. Albans, Vermont, next year as it sees increased demand ahead.RELATED ARTICLESDetermining Sub-Slab Rigid Foam ThicknessPolyethylene Under Concrete SlabsBuilding a Foam-Free HouseFoamglas Exits U.S. Residential Market In a telephone call, AeroAggregates CEO Archie Filshill said that he and a colleague were introduced to the technology in Norway six or seven years ago. After a round of testing in 2016, AeroAggregates began producing foamed glass in 2017 and now distributes it in an area from Massachusetts south to Virginia Beach and west to Pittsburgh. One of its chief uses is as a replacement for the Styrofoam used for soil reinforcement, stabilization and backfill in infrastructure work — highway, rail and bridge projects. Interest among state transportation officials grew when they realized the material, unlike polystyrene, wasn’t flammable and wouldn’t melt when exposed to gas or diesel fuel, Filshill said. Later, Filshill saw potential value in the use of foamed glass as backfill on construction sites. Because it’s lighter than stone, it’s easier and less expensive to transport, and it can be used as a replacement for the rigid foam and crushed stone that’s now used under concrete slabs by many builders. “It’s acting as a drainage layer, a capillary break, and as an insulating later,” he said. Among its biggest customers are New York City contractors who specialize in green roof systems, Filshill said. Foamed glass is 80% to 90% lighter than stone aggregate — between 10 lb. and 20 lb. a cubic foot — and can be placed on a 1:12 roof slope without any reinforcement. In residential construction, Filshill said, builders who are now using rigid polystyrene insulation and crushed stone under slabs could switch to foamed glass for about the same cost. “This gets placed like gravel so you replace your gravel layer with this and that would also act as your insulation layer. So you’re getting a two for one replacement. It’s easily put in, and there’s no waste.” Filshill said the insulating value of 12 inches of foamed glass ranges from R-11.5 to R-15.7. Costs run between $70 and $80 per cubic yard. “There is also a slight savings on installation,” he added, “because the material just gets dropped and plate-tamped, which you’re going to have to do with your stone base anyway.” Filshill said foamed glass also could be used as backfill around foundation walls, and as a free-draining fill behind retaining walls and under patios. Recycled glass mixed with a foaming agent and heated to 1,800°F becomes a lightweight, insulating material that can used in a variety of construction applications. (Image credit: AeroAggregates) Foamed glass is manufactured in a gas-fired kiln under license from its European developer. Powdered glass is mixed with a foaming agent and when heated to 1,800°F the soft glass becomes infused with bubbles. Although the kiln is gas-fired, Filshill said, foamed glass has half the carbon footprint of polystyrene and expanded shale, another lightweight aggregate option. Welcomed by advocates of foam-free construction Glavel’s website lists many of the same benefits as AeroAggregates, including high compressive strength, light weight, low thermal conductivity, and cost effectiveness. Company CEO Rob Conboy said Glavel grew out of a Passive House conference he attended in Germany in 2016. He was scouting for European technology that could be used to lower the cost of energy-efficient construction in the U.S. Foam glass is used extensively there, he said, but is not widely known in North America. But interest has been strong among builders who are looking for foam-free products. “We’ve got some fairly good sized roof projects as well as some folks who are foam-free practitioners looking to use the product,” he said. “We’ve had multiple conversations in multiple channels about how do they look to standardize foam glass gravel in their construction specifications.” Glavel sells for between $85 and $100 per cubic yard on the east coast (orders have gone as far as Seattle). When you calculate the installed cost of XPS or EPS with labor and gravel, Conboy said, “we are very cost-competitive and in some cases we might be cheaper.” When compacted to about two-thirds of its original loose depth, the insulating value of foam glass aggregate reaches about R-1.7 per inch, according to its Vermont importer. (Image credit: Glavel) Compaction is key to performance. The material offers thermal performance of R-1.7 per inch, but only after it has been compacted by about one-third. So, Conboy said, a subslab layer performing at R-10 (equal to 2 inches of XPS) would require between 9 and 10 inches of loose glass foam that would be mechanically compact on site. Glavel’s two production lines will use some 15,000 to 17,000 tons of recycled glass to produce 140,000 cubic yards of foam glass per year. “We think there’s a bright future for foam glass gravel,” he said. “We love the fact that we’re going to be taking something of little or no value and turning it into a product that’s good for the planet and an amazing alternative to a petroleum-based product that’s laden with lots of chemicals, and do some good.” Talking with potential retail partners Both AeroAggregates and Glavel are of interest to 475 High Performance Building Supply, a New York-based retailer specializing in foam-free building products. “We’re very bullish on it in the long term,” said Chief Operating Officer Ken Levenson. “We think it’s a win-win-win once you’ve got the supply chain and the manufacturing together. You’re taking recycled glass and upcycling it into an insulation product for buildings. It’s one of the few products that has this magical, virtuous cycle — how we can build and not just minimize our impact but have a positive impact.” Foam glass is especially interesting because it serves two purposes — drainage and insulation — and that ultimately simplifies the construction process, he said. “The big issue obviously is cost, and that’s really about having demand at scale and production that’s local,” Levenson said. “It’s not like you can just build a factory in Indiana and ship it all over the country and compete.” The company has been talking with both AeroAggregates and Glavel and trying to help them introduce foam glass to more potential customers. But for now, 475 isn’t listing the product on its website. “It’s a product we want to support and see how we can help it grow,” Levenson said.