Higher Green Roof Performance

Increasingly, North American stormwater regulations require rainfall to be managed within the property lines of any given development. In the urban setting, where virtually the entire site is consumed with structure, the rooftop is often the only available place to manage stormwater. Therefore, green roof performance is critical in order to meet stormwater management goals. Maximizing stormwater retention capacity of green roofs is paramount, and relying on aggregate media to perform that function is – to be blunt – inefficient. Green roof stormwater management can be greatly enhanced with alternative materials that complement aggregate media. The aim of the Mineral Wool in Green Roofs white paper is to provide compelling evidence that documents this proven green roof technology, utilizing case studies and test protocols designed to simulate green roof conditions. This report also includes some guidelines for best practices in the use of mineral wool in green roofs.

Mineral wool is a renewable resource with qualities that are highly desirable to improve green roof performance, including high water retention, low weight, durability, dimensional stability, and excellent horticultural properties.

 

Mineral wool has been successfully used in German green roofs for the past three decades and continues to be used in green roofs today throughout Europe and China. Despite mineral wool’s long and successful history overseas, it remains underutilized in North America. Many specifiers are unfamiliar with how to use mineral wool to improve green roof performance. With deeper appreciation of its history and use, these concerns should shift to comfort. Equally, the change to emergent technologies has the potential to upset established market forces and trigger efforts to sow fear, uncertainty, and doubt; however, this paper uses evidence and data to define mineral wool as a proven technology to improve green roof performance.

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Report Conclusions

Absorbent	Mineral wool is a high efficiency component to improve green roof stormwater retention.
Lightweight	Mineral wool has a very low dry weight, allowing the green roof assembly to be lightweight.
Horticultural	Mineral wool is an excellent horticultural medium in green roof applications.
Stable	Mineral wool is dimensionally stable in densities as low as 8pcf, optimally 10-12 pcf.  Mineral wool retains material integrity for at least 30 years in exterior applications, likely far longer. Use of a phenolic resin binder is likely to improve dimensional stability.
Durable	Mineral wool tolerates expected levels of foot traffic in green roof applications, exhibiting long-term resiliency to short-term cyclic compression, for reliable long-term green roof stormwater management.
Clean	Mineral wool is chemically stable when unbound or bound with phenolic resin. Runoff from mineral wool exceeds the EPA’s standards for drinking water.
Renewable	Mineral wool is a renewable material, utilizing dolomite or basalt – some of the few renewable rocks, and/or slag – a waste stream product.