Whether you’re a builder focused on high performance construction, a design team looking to specify foam glass gravel, or a homeowner taking on a DIY project, Glavel is your low carbon solution to insulating below slab and decarbonizing from the ground up.
Here you’ll find everything you need to get started, from what Glavel is and why it matters, to how to plan, install, and source it for your foundation. With simple guides, technical support, and sustainability insights, we’re here to help your foundational projects goals.
Residential Construction Technical Guide
Step-by-step quantity calculations:
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Square footage × install depth (ft) = compacted volume in cubic feet.
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Multiply by 1.25 to account for compaction = loose volume in cubic feet.
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Divide by 27 to convert cubic feet to cubic yards.
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Divide by 3 to find the number of 3CY bags.
Project Overview
Bishop Passive House is a single-family home in San Luis Obispo, California. This certified Passive House Institute home designed by Cairn Collaborative uses approximately 85% less energy than the average newly constructed home in California.
Design Challenges
Achieving both environmental and interior comfort goals required continuous insulation and high R-values to eliminate thermal bridging. The design team’s challenge was to build a home that performs in all weather conditions while using materials that align with sustainability goals.
Glavel as a Solution
Glavel played a crucial role in addressing the design challenges of the Bishop Passive House. Foam glass gravel provided continuous insulation beneath the slab, eliminating thermal bridging and contributing to the home’s airtight construction. Glavel met the project’s sustainability goals and helped achieve energy efficiency goals as well. By building with Glavel, the Bishop Passive House was able to maintain consistent interior temperatures with minimal space conditioning, contributing to its 85% reduction in energy usage compared to standard homes.
Some of the Organizations Building With Us
Product Basics
Foam glass gravel is a lightweight, insulating aggregate made from 100% recycled glass. It serves as both insulation and drainage in subslab insulation systems, replacing rigid foam board and crushed stone.
Foam glass gravel has been produced in Europe for decades. Glavel has been manufacturing foam glass gravel in Vermont since 2022.
Foam glass gravel is also be referred to as foamed glass aggregate, FGA, or cellular glass insulation.
Recycled glass is ground into a fine powder, then mixed with glycerine and sodium silicate and heated in a kiln to 1,500°F. This process creates a closed-cell, lightweight, insulating material with high compressive strength.
Performance Properties
Glavel has an R-value of 1.7 per inch. Because it’s a closed-cell material, it does not absorb water, so the R-value remains stable in damp conditions. Unlike foam board, its thermal performance doesn’t degrade over time due to moisture exposure.
Glavel weighs 10 lbs per cubic foot before compaction, which is 85% lighter than traditional gravel.
Glavel’s compressive strength is 110-125 psi at 25% compaction, making it suitable for residential slabs.
Ordering Overview
Glavel is only available directly through the manufacturer.
We regularly ship Glavel across the Northeast and Mid-Atlantic. We’ve also served projects in the Midwest and beyond. Shipping feasibility depends on volume, freight availability, and lead time.
You can place an order by calling or emailing our sales team. We’ll walk you through quantity estimates, shipping options, and delivery timing.
Glavel is ordered in 3 cubic yard increments. Use your project’s square footage and assembly depth to calculate volume. Take the 25% compaction ratio into account when calculating volume. For example, a 1,000 sq ft slab with 12” of Glavel would require approximately 45 cubic yards.
We accept check, ACH, and credit card. Payment is due at the time an order is placed.
Delivery Details
We regularly ship Glavel across the Northeast and Mid-Atlantic. We’ve also served projects in the Midwest and beyond. Shipping feasibility depends on volume, freight availability, and lead time.
You can place an order by calling or emailing our sales team. We’ll walk you through quantity estimates, shipping options, and delivery timing.
Glavel is delivered in 3 cubic yard bags on pallets via 53’ flatbed or 26’ box truck. Smaller projects or sites with limited truck access should use a box truck.
Unloading is the customer’s responsibility. You’ll need an excavator, skid steer with forks, or similar equipment. Customers are typically able to unload trucks in an hour.
Pickups can be arranged from our facility in Essex, Vermont. You must schedule in advance and bring a vehicle rated for the weight and volume. We’ll assist with loading.
A standard slab on grade assembly requires a Glavel layer wrapped above and below with a geotextile, with a vapor barrier and concrete slab atop.
Glavel should be compacted to at a 1.3 : 1 ratio (roughly 25%). Overcompacting is unnecessary and will not increase R-value or load bearing capacity.
Use a lightweight vibratory plate compactor (<200lbs). A smooth-drum roller may be used for larger areas. Avoid heavy tampers or compactors, which are too heavy to successfully compact Glavel.
Glavel supports passive radon systems. We recommend wrapping radon pipes with geotextile to maintain airflow. Active systems may slightly impact thermal performance and should be reviewed with your energy modeler if insulation levels are critical.
Some engineers will allow footings to bear directly on Glavel, but it must be evaluated case-by-case. Always consult your structural engineer for load-bearing applications.
Accordion Content
Installation Intel
A typical residential subslab assembly includes:
– Concrete slab
– Vapor barrier (such as Stego 15mm)
– Geotextile fabric (such as Mirafi 140n)
– Compacted Glavel
– Geotextile fabric (such as Mirafi 140n)
– Compacted subgrade
Glavel replaces both insulation and crushed stone, reducing layers and simplifying installation.
Glavel should be compacted 25% at a maximum lift height of 15″ (which would compact down to 12″). Overcompacting is unnecessary and will not increase R-value or load bearing capacity.
Use a lightweight vibratory plate compactor (<200lbs) to achieve even compaction. 4-5 complete passes will achieve the necessary 25% compaction. A smooth-drum roller may be used for larger areas. Avoid heavy tampers or compactors, which are too heavy to successfully compact Glavel.
Yes, Glavel supports passive radon systems. We recommend wrapping radon pipes with geotextile to maintain airflow. Active systems may slightly impact thermal performance and should be reviewed with your energy modeler if insulation levels are critical.
Accordion Content
It depends. Some engineers will allow footings to bear directly on Glavel, but it must be evaluated case-by-case. Always consult your structural engineer for load-bearing applications.
In certain cases, yes. You can insulate the exterior of stem walls by using Glavel as loose or compacted fill, as long as it is capped and not left exposed.