Buildings
Lightweight fill for green roofs, plazas and roof decks
Enviro-Rock is installed in raised patios and green roofs where strict structural load limits must be met[1], at about 200 kg/m³ (12.5 lb/ft³) loose.[2]
- 1Planting
- 2Growing medium
- 3Foam glass aggregate: light, free-draining layer
- 4Waterproofed roof deck
A foam glass aggregate layer between the roof deck and the growing medium adds little dead load and drains to the roof outlets. Schematic, not to scale.
Green roof and plaza fill
The engineering problem
Every layer on a roof slab or podium deck is permanent dead load. Mineral soils and aggregates used to shape grades, drain water and fill deep planting areas weigh about 1,500 to 2,400 kg/m³ (95 to 150 lb/ft³)[3], and the structural design sets a hard limit.
Water adds more. A layer that holds water raises the wet load, and a layer that does not drain lets water sit on the membrane.
Expanded polystyrene (EPS) geofoam blocks are lighter still, but FHWA notes that EPS is inherently flammable[3], and block shapes are hard to fit into narrow or irregular areas.[4]
Benefits
What Enviro-Rock adds
01
Lower dead load
Enviro-Rock weighs about 200 kg/m³ (12.5 lb/ft³) loose and 240 kg/m³ (15.0 lb/ft³) at 20% compaction, dry[2], against 1,500 to 2,400 kg/m³ for mineral soils and aggregates.[3]
02
Drains to the outlets
Its open, granular structure lets water move through the fill rather than collect in it[5], and as a loose aggregate it fills irregular shapes that blocks cannot.
On site
How it goes in
- 1
Protect the membrane
Install the protection layers the roofing system requires, then a non-woven geotextile below the aggregate.[8]
- 2
Place and shape
Spread Enviro-Rock to the grades and depths on the drawings; lightweight fill over structural roof slabs and deep-fill rooftop assemblies are listed uses.[9]
- 3
Compact lightly
Compact with a plate compactor on 150 to 300 mm loose lifts, using more passes rather than more vibration, and no jumping jack.[10]
- 4
Specs that matter here
Key properties
| Property | Value |
|---|---|
| Dry bulk density | 200 kg/m³ loose (12.5 lb/ft³)[2]240 kg/m³ (15.0 lb/ft³) at 20% compaction. For design, use a moist, compacted unit weight: PennDOT practice and the Illinois Tollway design guide use 376 kg/m³ (23.5 lb/ft³) for foam glass aggregate[12], and the Kelowna design used about 2.5 kN/m³ compacted.[13] The engineer of record sets the project value. |
| Confined compressive resistance | 1.01 MPa (147 psi) at 20% deformation[2]0.56 MPa at 10% and 1.67 MPa at 30%.[2] Tested by modified EN 1097-11.[14] An index value for comparing aggregates, not an allowable bearing pressure. |
| Water absorption | 7.2%, uncompacted[2]A weighted average by modified ASTM C127.[15] Absorption of foam glass aggregate rises with soaking time: Indiana DOT specifies 30 to 60% by weight after 28 days.[16] Allow for in-service moisture in the design unit weight and thermal values. |
| Intergranular void space | 50% loose, 30% at 20% compaction[2]The brochure notes these figures are based on worldwide averages. Open-graded, so water drains through the fill and capillary rise is interrupted.[5] No permeability value is published; ask for a test if the design needs one. |
| Fire | Glass; does not burn[6]No fire test to a named standard, such as CAN/ULC-S114, has been published for Enviro-Rock. |
Industries
Who builds with it
Questions
Green roof and plaza fill: common questions
What weight should the structural engineer use?
Use a moist or saturated weight, not the dry loose 200 kg/m³.[2] Highway design practice uses 376 kg/m³ (23.5 lb/ft³) for compacted, moist foam glass aggregate, and Finnish data compiled for the Illinois Tollway report gives 270 to 530 kg/m³ long term in a road structure and 600 kg/m³ under water.[11] The structural engineer sets the roof value from these and from Enviro-Rock test data.[14]
What can I use to fill a large planter to reduce weight?
A lightweight, free-draining aggregate under the growing medium. Enviro-Rock is used for deep-fill rooftop assemblies[9], with geotextile between the aggregate and the soil above.[8]
Can foam glass aggregate be a green roof drainage layer?
Yes. Green roof build-ups are a listed use[9], and the open structure drains freely; outlet conditions still have to be part of the roof design.[5]
Will foam glass aggregate float like foam?
It is buoyant if it is submerged[11], so the roof drainage must keep water from backing up into the layer, and the cover above holds it in place. Drainage and outlet conditions belong in the project design.[5]
Can it go under pavers and pedestals?
Yes, beneath pavers and pedestal systems where the design calls for it.[9] The structural engineer checks paver and pedestal loads on the fill.
Sources
- [1] Enviro-Rock building construction brochure (metric), Enviro-Corp Recycling
- [2] Enviro-Rock civil infrastructure brochure (metric), specification table, Enviro-Corp Recycling
- [3] Alternative Backfills for Highway Applications: State of the Practice (FHWA-HRT-23-110), 2024, Federal Highway Administration, Turner-Fairbank Highway Research Center
- [4] Lightweight and Sustainable Materials in Engineered Fills (FHWA-PA-2021-011), 2021, Pennsylvania Department of Transportation and Temple University
- [5] Enviro-Rock benefits: drainage and permeability, Enviro-Corp Recycling
- [6] Enviro-Rock cellular foam glass aggregate, Enviro-Corp Recycling
- [7] Enviro-Rock benefits, Enviro-Corp Recycling
- [8] Enviro-Rock installation guide, Enviro-Corp Recycling
- [9] Enviro-Rock applications: green roofs and terraces, Enviro-Corp Recycling
- [10] Enviro-Rock compaction equipment sheet, Enviro-Corp Recycling
- [11] Applications for Foamed Glass Lightweight Aggregate, final report with draft special provision and design guide, 2025, Illinois Tollway Research Program; Washington State University, Lafayette College and UW-Madison
- [12] Applications for Foamed Glass Lightweight Aggregate, final report, Illinois Tollway Research Program, Washington State University et al., 2025
- [13] Case study: 6-storey building, Kelowna, Enviro-Corp Recycling
- [14] Enviro-Rock technical data, Enviro-Corp Recycling
- [15] Enviro-Rock benefits: closed-cell structure, Enviro-Corp Recycling
- [16] 904-M-076 Lightweight Aggregate, Indiana DOT, 2025
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