Greening the urban environment
The twin towers of Milan’s Bosco Verticale – with their 900 trees and over 2,000 plants – are perhaps the most well-known and eye-catching ‘living buildings’, but today even the iconic Empire State Building is benefiting from areas of green roofing in a trend that has swept the world. Nonwovens are critical components in all such infrastructural projects.
The installation of grass and other plants on a building’s roof has a number of benefits, not least in absorbing rainwater and releasing it slowly back into the atmosphere through evaporation or, if there’s too much build-up, allowing the water to trickle slowly into drainage systems and ensuring they aren’t overwhelmed.
There are other benefits too, including insulation and cooling properties for the building and the promotion of biodiversity in built-up areas.
This has seen green roofs become important elements in many countries and in addition, being highly visible, they also very effectively provide a distinctive image to buildings and development projects.
As INDEX™20 exhibitor Freudenberg Performance Materials explains, nonwovens are employed in green roof structures as carriers for bituminous membranes, as drainage and storage layers as filter media, and in many cases, as the nutrient substrate.
For projects such as the Bosco Verticale, Freudenberg has supplied glass-fibre reinforced polyester nonwovens made from recycled PET bottles as the basis for permanent roof greening.
The application is a natural extension of the company’s long experience in the fields of both roofing membranes and geotextiles for which Freudenberg now recycles around seven million PET bottles a day at its European facilities in France and Italy.
Combining the flexibility of polyester with the stability of glass creates excellent runnability, particularly at higher temperatures and for use in bitumen production lines. In addition, the bitumen membrane creates excellent long-term dimensional stability and endurance. The use of glass reinforcement also eliminates the phenomenon of thermal memory – once installed on a roof, the membrane will no longer shrink when temperatures fluctuate.
Bitumen roof membranes last more than 20 years on average, after which, the damaged roofs are completely replaced or the damaged points repaired. This is an important advantage of this technology compared to other sealing systems, particularly in maintenance work. Manufacturers can also recycle waste from bitumen roof membranes by grinding them into a powder which can then be used as a raw material, further improving the sustainability of the product.
Another INDEX™20 exhibitor, Technical Absorbents, has meanwhile recently been involved in the development of a new product containing its superabsorbent fibre (SAF) technology for green roof installations.
“SAF technology can greatly improve green roof installations, due to its ability to absorb up to 200 times its own weight in water, creating a much bigger reservoir than would otherwise be possible for feeding the vegetation,” explains Technical Absorbents applications and development manager Mark Paterson.
The superabsorbent fibres have been blended with natural fibres and ultrasonically laminated between two sheets of spunbonded nonwovens in a patent-pending process to form a product called Living Roof Lite, which is promoted by the green roofing specialist Aquaten.
Living Roof Lite is a portable, pre-fabricated and stand-alone sheet that works on either flat or sloping roofs and significantly reduces run-off. Optimum evapo-transpiration properties allow the material to re-charge over a three-day period.
It is also able to withstand degradation from the wind and rain, and from the sun’s UV rays for a minimum of five years. It can be self-bonded to most commonly-used roof surfaces including asphalt, slate, concrete and terracotta tiles, PVC and HDPE.
“Throughout the world there is an abundance of existing building stock that creates a huge impermeable surface that has no value for wildlife or rainfall attenuation and creates a massive increase in the urban heat island effect,” says Mike Cotton of Aquaten. “Vegetating this available space and reducing its impact on flooding is seen as a key driver at local and government level. The current barriers are logistics, weight and perceived cost. Existing green roof systems are clumsy, inefficient, messy, heavy and costly and the disruption from logistics where cranes and large transport are required make retrofits an aspiration.”
Empire State building
Nonwovens and technical textiles manufacturer Low and Bonar, through its Xeroflor subsidiary, is another specialist in green roofing, and was involved in the $550 million ‘green’ retrofit of The Empire State Building which has reduced its energy consumption by some 38% annually.
The lightweight Xeroflor green roof system was installed on the 21st, 25th and 30th floors where as well as enhancing green space, it also reduces the overall air conditioning requirement and protects against storm-water runoff.
For the 25th floor roof, which gets little direct sunlight, a system which weighs just 20 kg/m2 when dry and 40 kg/m2 when saturated was installed, while for the inaccessible 30th floor roof, a pre-vegetated sedum mat with 19mm of XeroTerr – a resilient and low-maintenance nonwoven – was employed. All the heat and drought-tolerant plants in the mats were grown at local, independently-owned farms. The Xeroflor green roof system combines a variety of nonwovens, as well as polymeric entanglements fused to further nonwovens, for the growing medium, the distribution and storage of water within the root zones, excess water drainage below vegetated layers and the prevention of root encroachment into the structure of the building.