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Mineral Wool in Green Roofs – From Zero to Hero?

Green Team at Green Roof Technology, - Saturday, April 13, 2019

 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.

World’s First Modular Green Roof System

Green Team at Green Roof Technology, - Sunday, February 12, 2017

World’s First Modular Green Roof System

Modular Green Roof System

Green Roof Professionals around the globe often wonder or speculate how and when the commercial modern Green Roof industry really took off. There are many opinions and alternative facts out there but only a few really know that the hot spots with patents were in Basel Switzerland and in Stuttgart Germany for seamless or wall-to-wall Green Roof systems.

The World’s first modular (or tray) system has been developed in Stuttgart by Brecht and Hämmerle, mainly known as the Brecht System (if one doesn’t consider terracotta pots on roofs as a modular system).

The Brecht System was a basic polystyrene box with a three-layer Green Roof system. The system was available in extensive, semi- intensive and intensive planting depth. With this simple three-layer system the inventor combined many benefits in one box. All systems had a water reservoir for maximum water retention – more than any other Tray system currently on the market and more than any fabrics, foams or mineral wools, and the boxes contained standard nursery soil for a healthy fast growth and to lower costs.

There were different options for covering the less attractive boxes, with either wood or metal (aluminum). Today we call these frames around the boxes: Edging.  

Based on the polystyrene, the boxes were very lightweight and easy to install. Actually, they fitted into each other to create different heights and different planting depths. I would describe them as a Modular –LEGO-like planting system.

Unfortunately, any polystyrene as a limited lifespan when exposed to UV or biological activity and so many of these roof gardens had problems after 5-10 years. Further, many of the plants rooted out of the boxes (drainage holes) and penetrated the waterproofing.

Around 1992 the last Brecht System was removed and replaced by wall-to-wall or seamless Green Roof systems. All of these Green Roofs are still existing - if the building still exists.

The Brecht Modular Green Roofs system had also other issues that are similar to the currently existing systems. However, nowadays the tray systems use metal, other plastics, and mainly with irrigation systems. This makes them last longer, but as often only delays the point of failure. The roots of plants and the biological activity on healthy Green Roofs are often underestimated as well as the functional lifespan of foams, polystyrene drainage mats, and mineral wool products.

The Best Green Roof System

Green Team at Green Roof Technology, - Saturday, August 01, 2015

The main purpose of an extensive Green Roof is stormwater retention and delaying stormwater runoff amongst many other added values.

Above: An Irrigated thin layered Green Roof System – without irrigation it would be dead.

In the last decade in North America, we've seen many Green Roofs where the intended plants never really flourished. I estimate that in the US at least 50% of the green roofs are not performing to their fullest potential. This can be observed by simply looking at the most obvious of indicators, the plants themselves, regardless if they were planted on purpose or somehow found the space to take root. 

Most of these less healthy extensive Green Roofs are thin-layered systems, pre-planted boxes (often called modular systems or hybrid systems), Green Roof Systems from roofing manufacturers with ineffective components, single source warranty-systems, or design intents without consideration for the needs of plants. Typically these systems much more costly (whether thin or thicker) and the mid to long term results are often far below systems that are assembled in place with common sense.

 

Thin-Layered system with irrigation - doesn't work and doesn't retain much water

We all know that the transition from being a common nursery-grown plant (including pre-planted boxes) to the extreme environment of a rooftop poses severe challenges. Green roof plant nurseries typically have "great" advice and recommend the installation of temporary or permanent irrigation systems. In some areas this might be helpful when operated correctly but in all cases this advice is defeating the purpose of an extensive Green Roof (water retention). In almost all cases any type of irrigation caused a spiral of failures and it is wrong to irrigate extensive Green Roofs in areas with limited water for the cause of just having a green roof (Green Washing). Most company sponsored experts don’t see the entire picture or they only see the short term profit and commission (“Mow-Blow-Go”).

If a problem occurs and since many Green Roof system developer lack the proper and specific green roof horticultural knowledge, they may not be able to identify problems by simply looking at the indicators (the plants). This could cause the problem to gain momentum. In addition, the false conclusion that technology (Google search, Apps, synthetic growth media or sophisticated soil moisture control devices) can fix the problem supports my theory of hardly experienced or misinformed green roof professionals. They rely heavily on technology to fix any issues and miss the big picture.

Nature has the ability to take care of itself, as long as the appropriate design, materials and plants are used in addition to being familiar with the immediate location and climate.

Thin layered, super lightweight systems or systems with “innovative” components are just by physics not meant to retain “more” stormwater for the plants or they retain too much water for specific plants. As a matter of fact the costs for retaining stormwater in thin layered systems are extremely high comparing to a standardized extensive Green Roof with a thickness of 4-6 inch (depending on location). Besides the initial costs the lack of water retention (don’t forget all studies are done by the companies!) won’t support any significant bio diversity plus the operational costs (because of the required irrigation) are tremendous over time. Typically these Green Roofs never pay back with they are not utilized for “Green Washing” purposes in advertising.  

Irrigated extensive Green Roofs and/or thin layered, super lightweight systems (below 25 lbs/sf) will increase the nutrient pollution in runoff, require higher fertilization application, have hardly any tendency for self-healing, and may increase the pressure of unwanted plants and have a high risk for failure. Irrigated extensive Green Roofs are not environmentally friendly in most loactions!

Green roof designers and green roof professionals must understand that certain advertising, studies, White Papers or project references are all assembled by specific manufacturers and their goal is to make money – unfortunately on the back of a very advanced technology and on the back of their clients.

When we advise our clients they get the full picture because we have seem all solutions in the last 35 years, we have tested them and we are currently working millions of square feet where these systems require upgrades, reinstallation or massive repair (around 20 million in damage so far).

We also help our clients doing it as efficient as possible and to get their money back from prior failures through warranty claims and sophisticated lawsuits. This might help to standardize the function of Green Roofs and helps to get the black sheep out of the market. The building owner has a right that things are done right from the beginning.

Never irrigated in the last 10 years.

Mineral Wool on Green Roofs

Green Team at Green Roof Technology, - Sunday, September 21, 2014

 Green Roof Innovation

 Mineral Wool on Green Roofs

 Green Roof Technology Reveals Latest Study about Mineral Wool on Living

Since their first commercial production in 1871 (Georgmarienhütte, Germany), mineral wool found its way in many applications like thermal insulation and soundproofing. Mineral wool, mineral fibers are typically referred to synthetic materials like fiber glass, ceramic fibers and stone or rock wool.

Two main types of mineral wools are on the market – water repellent (Hydrophobic) and water adsorbent (Hydrophilic). For horticultural purposes, only the hydrophilic type is useful. Many patents were granted for simple Hydroponic systems or the germination of seeds with mineral wool in the early 80’s.

In modern green roof technology the first green roof systems came on the market around 1985 in Germany at a time as the German green roof industry gained tremendous momentum. As a lightweight solution with high water retention, mineral wool seemed an ideal material. The higher costs and the higher carbon footprint - comparing to lightweight aggregates – were argued with easier installation and higher water retention.

Extensive research over more than 5 years at the University of Geisenheim and on numerous buildings confirmed the high water retention properties. However, in the mid-run these tests also revealed that the performance and the health of the vegetation were far below conventional green roof systems with standardize green roof components. Mineral wool manufacturers and green roof system suppliers stepped away from the idea of using mineral wool as a growing component for green roofs.

“Today we can see a revival of mineral wools in the green roof industry,” says Jorg Breuning, CEO, Green Roof Service LLC,” in countries with hardly any green roof experience, mineral wool is getting rather popular with potentially fatal results in the mid and long-run.” 

Especially in the United States, the market is growing rapidly for mineral wools on green roofs, disregarding existing studies and without extensive long-term tests. It isn’t even proven whether certain fibers can cause health problems, leach out chemicals or whether these components can be recycled when the green roof doesn’t perform anymore.

In 2012, the lack of performance of mineral wool as a vegetation carrier resulted in a major green roof restoration at Amsterdam International Airport. 90,000 square foot of green roof – built with mineral wool - had been taken off and replaced by a standardized green roof system. At this point, this was the largest green roof restoration in the history of mineral wool on green roofs. Costs that could have been avoided.


Doing it right in the first place.

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