Insulating Gravel
The relatively high price of this foam-glass foundation base material is offset by the lack of a need for rigid foam sub-slab insulation.
Insulating a subslab has traditionally been a multistep process that calls for compacting and leveling the subbase (often gravel), followed by the addition of one or more layers of board insulation. A Vermont-based company is now reducing that process to one step with the creation of compactable, foam-glass gravel.
The product, Glavel, weighs 9 1/2 lb. per cu. ft.— about 5% of the weight of stone gravel—and is delivered in 3 1/2-cu.-yd. bags. Once poured into place, it is compacted just like ordinary gravel (at a ratio of 1.3:1) to create a minimum 6-in.-thick base. It offers a compressive strength of 54 psi—enough for most, if not all, residential subslab applications—and yields an R-value of about 1.7 per in.
The price is perhaps the most surprising piece of information about Glavel. The material sells for between $85 and $100 per cu. yd. on the East Coast (nationwide shipping is also available), but once you factor in the labor savings, this product becomes close competition for conventional gravel and EPS or XPS insulation.
—Justin Fink, editorial director
From Fine Homebuilding #288
Read more about foundations:
Protecting Foundation Insulation – A heavy gauge of metal flashing offers increased durability.
Minimizing Concrete in a Slab-on-Grade Home – Whether your goal is to cut construction costs, minimize environmental impact, or both, there are practical ways to build a home with less concrete.
Insulation for an Airtight House – From the foundation to the attic, efficient materials and installation techniques yield just 0.4 air changes per hour.
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