Green Roof Guide

What Is a Green Roof?

Green roofs are a vegetated roofing system that takes place of a traditional flat roof. They typically come in the form of a layer of vegetation placed above a growth medium and drainage, which is separated from the base with a waterproof membrane. Benefits of a green roof system include rainwater retention, building sound + heat insulation, and a habitat for wildlife. The disadvantage of a green roof is that they can increase weight stress on a building structure. Foam glass provides a solution to keeping green roofs lightweight, mitigating building stress without compromising quality.

Since Glavel is both lightweight and closed cell, it can satisfy the requirements for a drainage layer underneath the growth medium while contributing to a lightweight green roof system installation. Foam glass can also be compacted up to 45° angles, allowing for landscape architects and designers to create angularity and shapes with their green roof designs.

Physical Characteristics of Foam Glass Gravel

Load bearing – 116 psi compressive strength at 10% deformation

Frost heave resistant – Will reduce impact of freeze and thaw cycles

High friction angle – Pieces allow for mounds and up to 45° slopes

 Water resistant – Closed cell structure facilitates drainage

Produced from recycled glass – Categorized as ‘clean fill’

Non combustible – Will not burn, nor propagate fires

Inert – Prevents rodents, termites, bacteria, and rot

Thermal insulation – R1.7 per compacted inch

Lightweight – 9.8 pounds per cubic foot

Green Roof Cross-Sections

Using Glavel as the bulk fill of a green roof system creates opportunities for engineers and landscape architects to build a flooring system that satisfies needs for both performance and aesthetic. Glavel foam glass is placed directly atop a vapor barrier / roofing membrane, which sits directly on the roof slab. The Glavel aggregate layer’s thickness and design can be altered based on project needs. Regardless of the shape of the Glavel fill, a membrane is placed atop the compacted Glavel, and the green roof system can be installed atop the membrane.

Glavel Technical Specifications


Delivery for green roof fill is done directly to job sites in 3 cubic yard bags. With a cinch at the bottom and straps on the top, bags can be maneuvered directly over a site and product can be directly released. Cranes can lift bags one at a time to get bags atop a roof prior to filling.

Glavel Bag Release

With Glavel as a green roof fill, structures will be under less physical stress, while the floor of the green roof system will remain seated and intact due to the interlocking nature of Glavel aggregate pieces. A green roof system can reinvent the bounds of green roof capability. For more about green roofs, visit the National Park Service Green Roof page.