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Greening roofs is as old as history itself and has got a long tradition in many cultures. Some people even say this dates back to the ‘‘Hanging Gardens of Babylon’. But the real breakthrough has been taken place since the last years. Green roofs become more and more popular all over the world. No matter if you’re looking to Germany, Scandinavia, Canada or even the Asian metropolises thousand square meters of roof tops turn into green and specialised companies launch new technical solutions. The area of newly built green roofs is increasing permanently: people create their individual havens of well-being. Companies spot that the roofs of their production and office facilities can turn into gardens and offer relaxation to their employees. Communities plant roofs of municipal buildings and set up subsidies. Universities and institutes put more and more effort in research to highlight the effects of green roofs… The reasons? Green roofs are a good alternative to

counteract recent environmental problems in urban areas.

They buffer rain water and thus unburden the canalisation and prevent flooding. They cool down buildings and thereby work against the heat island effect and safe energy costs for air-conditions. Additionally green roofs turn particulates into O2, improving the air quality. So, green roofs are a simple combination of positive impacts?

Green roofs are cool! Green roofs are thrilling, modern and fascinating!

Under the motto ‘The passion for comfort’ the Recticel

Group as Europe’s biggest

producer of polyurethane foam strikes to make a real difference in daily comfort for all, on-going with innovative

solutions in all our businesses.

Today, Recticel concentrates on four selected fields of application: Flexible Foams, Bedding, Insulation and Automotive. Although the group mainly produces semifinished products (Flexible Foams and Automotive), in a number of divisions it also manufactures finished goods, both consumables and durables (Bedding and Insulation). As market leader in most of its activities, Recticel provides work to more than 8,000 employees in some 120 establishments in 27 countries. The group operates predominantly throughout Europe, but it also pursues a number of activities in the USA and Asia. In 2009 Recticel realised a turnover of 1.3 billion Euro.

One of the recent innovations of Recticel is its unique hydrophilic product line Basically developed as substrate for the horticultural market, Polygrow® has been adapted to

Polygrow®. green roofs and walls.

Current challenges in urban areas Rural and urban population in 1950


Rural and urban population in 2009


rural population



urban population in economic developing countries urban population of economic developed countries


For about 50% of the world population urban areas are their home. In cities there are most of the flats, shops and working facilities. Everybody is living and working at close quarters. Having a mindful view on our surrounding, we notice that our cities look like concrete jungles: new streets and houses are built to solve the problem of missing housing space and increasing traffic.


Compared to people in rural areas the inhabitants of

noise, higher CO2 emissions, flooding and the heat island effect. cities have to struggle with much more

Climate differences – urban versus rural areas 5-15% more clouds and 5-10% more precipitation air humidity 8-10% less in summer 14% less snowy days and 2-3 weeks less frost

temperature in winter 1-2oC higher, in summer until 12oC higher CO2 emissions less wind but between skyscrapers more gusts

Green roofs against environmental problems in urban areas Green roofs and walls are an excellent alternative to counteract the environmental problems in urban areas. They are able to filter up to 20% of particulates in the air. They unburden the canalisation and enhance acoustic and thermal insulation. But green roofs can also turn into homes for plants and animals and create a connection between the urban areas and the countryside. Examplarily the following picture taken at the City Hall in Chicago shows how green roofs can help to cool down buildings and thus counteract the heat island effect in cities. But this has not only an impact on the environment but also on the energy and thus cost savings for the people. With a green roof it is possible to safe up to 4.15kWh/m2/a.

Green roofs in a nutshell! They‌ double the life time of roof surfaces neutralises acid rain between 10 to 30 years unburden the canalisation up to 10% ave. enhance acoustic insulation up to 8dB filter up to 20% of particulates in the air provide cooling inside buildings up to 3°C decrease energy costs up to 4.15 kWh/m2/a increase the efficiency of PV modules better biodiversity have a positive impact on people can increase the value of buildings

How to realise green roofs? Today, building a green roof means to take the decision of an extensive or an intensive one. Their main differences: the type of vegetation and the accessibility. As most simple green roof type extensive ones are usually planted with sedum or sedum herb mixes that need less maintenance. They are mainly suitable for water retention, cooling and air cleaning. By contrast roof gardens have got a great variety. They are used to walk on and enthuse the eyes of their visitors with lush greenery, a variety of plants and


sculpted walls. Basically, green roofs are applicable to both new buildings and renovations. Existing roofs may have a low load capacity, but extensive green roofs can be moslty realised. When planning a green roof it is necessary to care about several facts: load capacity roof pitch and height accessibility and safety accessibility of electricity and water climate and surrounding

Vegetation Height Irrigation Weight Walking possibility Water buffer Load capacity roof Maintenance

sedum, grass, herbs < 15 cm mostly not 50 – 150 kg/m2 no 4-12 mm normally always sufficient very low

Roof pitch

up to 45°


grass, shrubs, trees 25 – 100 cm always necessary 250 – 1 000 kg/m2 yes 18-39 mm requires an extra strong roof comparable with a normal garden flat or in terraces

Independent from the green roof type, their build-up is mostly the same. Usually a  root and water protection layer will be placed straight on the roof surface. It has to be strong enough to even withstand roots of tree (seedlings). Therefore special HDPE or LDPE foils are used. On top of the water and root protection layer  the drainage will be installed. Mainly consisting of plastic trays this layer manages the water balance: reservoirs store enough water that the plants can survive during dry periods and wholes guarantee that waste water can runoff easily. An additional  filter fleece takes care that the loose granules of the  substrate layer, the plant growing medium, don’t block the drainage. On top of the total system  the vegetation layer will be placed. This complexity guarantees a good water management and plant growth but also results in high costs for planning, transport and installation. When realising a green roof, these items need to be calculated with 30% of the total price. Due to the numerous layers and the heavy lava and soil mixes used as substrate both transport costs rise, on the road and vertical to the roof top. The same happens during installation: the more layers the more time is needed to get everything ready.

The unique solution for the next generation green roofs Future green roofs won’t only become more diversified and sustainable in their positive impacts on nature. Future green roofs also need to be more simplified systems that are not affecting deterrence by their complexity. They need to be selfexplanatory, cost effective and thrilling in one. It becomes important to point out a way of easy installation for everyone. This results in more installed green roofs and thus an increased positive environmental impact in urban areas. Polygrow® meets these future challenges by its unique 3in1 solution! This means that the Polygrow® slabs are acting as substrate, water buffer and drainage in one. There is no need to install three different layers separately. With Polygrow® it is possible to do this by one

unique layer. Polygrow® PG D2 slab

This simplicity saves material and handling costs and makes it possible for everybody to create his own green roof. Due to its light weight Polygrow® is saving additional costs in transports and is a good solution for light weight roof tops like industry buildings or carports.

Polygrow® profiling as drainage Polygrow® coating as additional water buffer

Polygrow® - more than a newcomer… Basically developed as substrate for the horticultural sector, Polygrow® has been already running its course since 2005. In cooperation with a leading substrate company and more than 50 growers around the world, this product had been customized to the needs of the branch. Tomatoes, cucumbers, sweet peppers and eggplants can be perfectly cultivated on Polygrow®. But innovation is the key driver of each business, and thus Recticel continued in the development of Polygrow® with focus on green roofs and walls.

The story of Recticel’s latest foam family, Polygrow®, began

1st generation of Polygrow®: incipient tests under real conditions in Dutch greenhouses

2nd generation of Polygrow®: expanded tests in greenhouses in the Netherlands and other European countries

3rd generation of Polygrow®: 70 test growers around the world agree that Polygrow is worth to be called “the new generation substrate”

Polygrow® is present at the market Recticel adapts Polygrow® to green roofs and walls

Polygrow速 in practice 速

In a few weeks, one of the biggest green roofs in Southern Europe will be realised. We are very proud that Polygrow had 2

been chosen for this great 11,000m project.

Initiator of the project had been the Adega


the first winemaker cooperative in Alentejo, Portugal. Founded in 1955 more than 320 winemakers joined Adega that commands an area of 2,200 ha vineyard. With a yearly production of 9 million litres of wine Adega is one of the biggest winemaker cooperatives in Portugal and already won a lot of awards.

Whitepaper greenroofs  
Whitepaper greenroofs  

Learn more about the challenges in urban areas and to which extent green roofs have positive impacts on them.