Mineral Wool in Green Roofs – From Zero to Hero?
The use of Mineral Wool in Green Roof applications is an increasing trend in North America and in countries where such industry is still young or focused on fast profits rather than on longevity.
One selling benefit of Green Roofs is the extended lifetime of the underlying water proofing because the Green Roof protects the roofing against the elements. Can Mineral Wool stand up to this?
Against any semi scientific promotional material from Mineral Wool applicators, the market share of mineral wool in the German Green Roof construction industry is around 0.1% or out of 100 million square foot new green roof construction every year (Germany) it is only around 100,000 sf/year.
The reasons for this marginal market share are simple:
- Mineral Wool has shown a drastic loss in performance after 5-7 years.
- Mineral Wool is engineered for nurseries and for only one growing cycle.
- Mineral Wool fibers are considered “hazard” in Europe.
- On extensive Green Roofs the water retention and water-air ratio is unsuitable for succulents.
- Mineral Wool expands and contracts in wet-dry cycles.
- Mineral Wool is hydrophobic and can dry out the traditional overlaying growth media faster.
- Mineral Wool growth media boards require ballast.
- Green Roofs with Mineral Wool are difficult to repair, replant or recover.
- Mineral Wool interrupts natural soil profiles (unnatural soil profile).
- Mineral Wool is an additional installation step and related to higher costs.
- Some Mineral Wool products compress under the load of ballast (soil).
- Some Mineral Wool products contain Phenol resin or Phenol-Urea-Formaldehyde resin as binder and these products can hardly be recycled. Ecose technology is environmentally better but it doesn’t eliminate other problems mentioned here.
- Reuse of all types of Mineral Wool for the same purpose is only possible after a (non-existing) difficult remanufacturing process.
An inexperienced green roof installer might like the idea of an obvious simple installation. However, what looks nice in a brochure doesn’t necessarily reflect the reality. Ballast on the Mineral Wool boards is still required and this requires different equipment. The setup costs for additional equipment are the same whether small or larger amounts of ballast ( or ballast reduces the setup costs).
Engineers might like the tremendous amount of water retention of Mineral Wool. However, they forget that plants (vegetation) have a very specific need for a balanced air-water ratio. If engineers plan the use of succulents (like Sedums) such air-water ratio is even more important (emphasis on air). Engineers are not horticulturalists.
Mineral Wool is widely used in nurseries for one-season vegetables. After this growing season the Mineral Wool (often combined with plastic) ends up on landfills. In 2008 it was around 200,000 tons of hazard waste in Netherland alone. Further, nurseries are growing their crops under highly computer controlled conditions for nutrients and air-water ratio in green houses. Who wants to sell a nursery to a building owner with roof under the sky?
In general shouldn’t we like Mineral Wool in Green Roofs? Mineral Wool gives us lucrative additional jobs in the future for repair or replacement (job security…).
Photo: Repair, Reuse - impossible
I am a lifelong green roof professional and I stand up to my principals with the promise that a green roof should last as long as the building – and that the materials can be reused for the same purpose after that and without processing (there are many fancy names in advertising for it, like cradle-to-cradle etc.).
Like me many people don’t care about fancy word creation and they stand for and what the American Green Roof industry should stand for uncompromised quality and doing things right. Quick profits, instant gratification or senseless warranties don’t promote the trade of professional Green Roofers and it is certainly not my philosophy.
Mineral Wool is: From hero to zero.
I appreciate reading my opinion, based on 4 decades of Green Roof experience from all Green Roof friendly places in the world.