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Lightweight Green Roofs

Mineral wool is a durable material, ideally suited for lightweight green roofs.

Mineral wool is an excellent material for achieving high stormwater management in lightweight green roofs. Mineral wool has an open fiber matrix that is typically over 90% void space. The fiber matrix is very lightweight, but voids within the matrix fill with water and retain water via capillary action, yielding a saturated weight that is only slightly higher than the weight of pure water.

Due to its low dry density, mineral wool should typically be protected from wind uplift. See “Best Practices” for more information.

lightweight green roofs: lightweight green roofs Rock wool is an easily handled component of a lightweight green roof system.


Mineral wool at 8-14 pcf Lightweight Green Roof Media
Dry Lbs/sf at 1 inch thick 0.67-1.17 4.5 +/-
Wet Lbs/sf at 1 inch thick 5.5 +/- 7 +/-
Lbs of water at 1 inch thick 4.5 +/- 2.5 +/-
Comparative wet and dry weights of mineral wool vs. lightweight aggregate green roof media.


Low weight is a highly desirable green roof characteristic, as many existing structures are unable to support the added load of a traditional aggregate-based green roof, but might be able to support lightweight green roofs.  Even new construction benefits from lightweight green roofs, as buildings can be built less expensively and more sustainably if structural demands are lower. In many ways lightweight green roofs are much more sustainable than heavier aggregate-based systems, as they utilize less material, require less energy to ship, and require less construction material in the building’s structural system.

lightweight green roofs: Wet and dry weights of mineral wool, a component of lightweight green roofs

Wet and dry weights of various grades of mineral wool. The vertical axis is pounds. The horizontal axis is wet/dry cycling trials as described in the full report



Read the full report: Mineral Wool In Green Roofs.