Frequently asked questions about Green Roofs

A. Advantages for the community

  • Water management
    In urban areas, there is a high degree of waterproofing (= large proportion of pavement in comparison to the total area). As a result, little or no precipitation can penetrate the soil, any such precipitation immediately flows to the sewer system via impermeable surfaces. Thus, even relatively small showers may cause a temporary overload of the sewer system, resulting in local flooding. This may be prevented by building larger sewers which may dispose of the water faster and in larger quantities. However, this is expensive and merely moves the problem to another area. Another solution is to immediately dispose of all precipitation (= increasing the retention of precipitation). This may be done in many ways, including through the construction of rainwater reservoirs or green roofs. The latter reduce the drainage of precipitation, meaning that peak flows are lower, the sewer system is not (or less) overloaded, and no (or less) serious flooding occurs. The ECCOsedum green roof system provides an annual precipitation discharge of 50%. There is no difference in water discharge between flat and sloping green roofs with a gradient up to 15°.
  • Air and water purification
    The urban environment is not only different from its surroundings in terms of climate, but also in terms of air pollution. A green roof may have a major influence on this as its complete system of vegetation, substrate, and micro-organisms not only captures, but also degrades harmful substances such as carbon monoxide, benzene, and dust particles. Green roof vegetation extracts dust and CO₂ from the air. In addition, it captures harmful substances such as nitrogen oxide, hydrogen sulphide, etc. and is able to encapsulate and immobilise noxious particles thanks to its stomata. In this way, green roofs contribute to a better environment through air purification. Furthermore, precipitation contains many harmful substances. If contaminated precipitation flows through a green roof first, part of the pollution is filtered before flowing into the waterways. Consequently, green roofs and other greenery have an important protective function.
  • Habitat development
    Buildings and other infrastructure take up space, as a result of which loss of habitat always occurs. Despite the fact that green roofs are not a full substitute for lost natural habitat, they may form an important landscape element for both fauna and flora. Green roofs may serve as a temporary habitat (as a stepping stone and as a temporary place of refuge), but also a replacement habitat and as a basic habitat. The extent to which certain plant and animal species are present depends on many factors such as the type of green roof, the manner in which the vegetation was applied, and the presence of flora and fauna in the area. In any event, blooming sedum plants are a major draw for butterflies and other insects that feed on nectar. In other words, green roofs may contribute to the increase of various plant and animal species (so-called biodiversity).

B. Benefits for the roof owner

  • Longer lifespan for roofing
    A green roof lasts longer than regular roofing (even twice as long compared to a flat roof with bitumen covering). The presence of the layered construction protects the roofing from:
    a. UV radiation: this breaks down materials due to the photochemical reactions; in case of a green roof however, the radiation is absorbed by the vegetation.
    b. heating, freezing, and temperature fluctuations of the roof: extreme and fluctuating temperatures cause friction in the roofing, as a result of which tearing occurs or seams may break (especially in case of bitumen roofing). A green roof tempers the temperatures through the presence of the vegetation and the substrate. This causes lower maximum temperatures and higher minimum temperatures, in addition to much smaller fluctuations in temperature. The extent to which temperatures are tempered depends on the thickness of the green roof.
    c. uneven heating of the different roof layers: this results in blistering and deformation of the seals. This is not possible with green roofs, because fast and extreme fluctuations in temperature do not occur.
    d. mechanical damage: roofs may become damaged by hail. In the case of green roofs, the impact of the hail is absorbed by the different layers.
  • Thermal insulation of the roof
    The aforementioned lower maximum temperatures and higher minimum temperatures are a result of the insulating effect of the green roof. Therefore, not only is the roof waterproofing subject to a more moderate temperature regime, but heating costs in winter and cooling costs in summer are also reduced, with the effect being the most pronounced in summer.
  • Sound insulation
    The green roof absorbs sound. However, the exact magnitude of the sound absorption is difficult to measure. The overall effect also depends on the surface and the structure of the greenery.
  • Visual benefits
    In addition to less extreme temperatures, higher humidity, and cleaner air, green roofs also contribute to a better living environment and health through their visual effect. A view of greenery has a positive effect on a person’s mood, and therefore on a person’s physical health. Furthermore, the look of a green roof changes with the seasons, resulting in a pleasant variation of the view.
  • Environmentally friendly image
    By creating a green roof, businesses will develop a more environmentally friendly image. Working in a green environment also has a positive psychological effect and may contribute to increased job satisfaction and thus a higher productivity.
  • Financial benefits
    Most people assume that a green roof is more expensive than a traditional roof. This is true only if one compares the cost of purchasing a green roof to that of purchasing a traditional roof, but the longer lifespan enjoyed by green roofs ensures that the price difference in the long term is minute or non-existent. All things considered, green roofs are more economical.

There are two parameters to consider during the installation process of ECCOsedum green roofs:

  • Prevention of washout or shearing of the substrate
  • Shearing of the entire green roof system due to the incline of the roof

For the above reasons, there is a limit to the roof incline. Based on the gradient and the corresponding customised roof structure, the following categorisation may be made:

  • Gradient between 0 and 3° (0 to 5%)
    The ECCOsedum system can be placed without any additional precautions.
  • Gradient higher than 3° (over 5%)
    The ECCOsedum system can be placed without any additional precautions, thanks to the specific construction of ECCOsedum green roofs, erosion protection is not necessary for these kinds of slopes.
  • Gradients higher than 15 to 20° (27 to 36%)
    Here, an additional system is installed to prevent the shearing of the substrate layer. Such systems can be divided into two groups. (1) Systems that reduce the gradient by means of a stepped system (similar to a terrace structure) or (2) systems that divide the substrate layer into compartments by means of a slat system. The distance between adjacent slats is determined by the gradient.
    --> Slat systems can in turn be divided into (a) slat systems installed underneath the roof waterproofing: these can be made out of wood and have a longer lifespan but require an additional protective layer if the slats do not have rounded edges. This is to prevent damage to the water-retaining layer. The additional water retention that may accumulate behind the slats will also have a negative impact on the shearing of the substrate later; or (b) slat systems that are installed above the roof waterproofing: The slats are generally made from plastic. For inclines up to about 11° (20%) they may also be made out of wood. The wood will decay over the years, but as the substrate becomes rooted throughout, the substrate layer is firmly anchored. A slat system that is installed above the roof waterproofing has the advantage of not influencing the roof waterproofing and not causing water stagnation.

Yes, because bee mortality is caused by (in order of importance):

  • the large amount of maize that is being planted: maize has pollen with a very low calorific value, so that bees assuming they have sufficient supplies for winter end up weakened by a lack of nutrition;
  • the presence of the varroa mite and parasitic fungi;
  • the use of pesticides. Note that this only comes in third place. Imidacloprid (Confidor) in particular is subject to heavy criticism. Complaints have also been voiced regarding the application of a mix of different pesticides. When examining garden plants, 57 substances were found, almost all of them legal, but classified by some environmental organisations as toxic and therefore as poisonous plants. As a result of these actions, chains and supermarkets are required to deliver plants that are free from any illegal and toxic substances. They are asking their suppliers to sign a statement to this effect.

ECCOsedum trays are cultivated with absolute respect for beneficial insects. The time of application and the choice of pesticide are crucial in this regard. The ECCOsedum nursery registers pesticides, fertilisers, and energy under the Ecas-certified MPS label.

The following parameters were taken into account while selecting plant types:

  • Aesthetic value (e.g. flowering): large variety of at least 10 sedum types.
  • Drought resistance depending on substrate thickness, substrate composition, and water buffering. Since each sedum type thrives best under slightly different climatic conditions, a large variety of sedum plants provides more security.
  • Speed of multiplication, this in order to prevent overgrow by one specific type
  • Regenerative capacity after extreme drought.

Different flowering periods: when pre-cultivating ECCOsedum green roofs, use is made of cuttings: these are offshoots of mother plants that are snipped off. To determine the proper dosage of sedum cuttings for each variety, it is important to know how fast they multiply after planting (to avoid monoculture). By making use of growing fields (mother plants), each with one type of sedum plant, the correct mix of cuttings can always be guaranteed, which is important for the variety of the green roof.

ECCOsedum contain at least 7 types of sedum:

  1. Sedum Immergrunchen
  2. Sedum Album
  3. Sedum Reflexum
  4. Sedum Sexangulare
  5. Sedum Acre
  6. Sedum Spurium
  7. Sedum Lydium

Although the list of benefits is long, there are two things that must be considered:

  1. Heavier construction
    The installation of a green roof adds weight to the construction. In most cases, the load-bearing structure is sufficiently strong to carry a green roof.
  2. Price
    The cost of purchasing a green roof is a factor that is not to be ignored, but green roofs are more economical in the long term. They do away with the need to invest in a (costly) drainage system, green roofs reduce temperature fluctuations (thermal insulation), and they mitigate sound (sound insulation), lastly green roofs ensure that your roofing will last longer because it is protected among others against UV radiation and hail.
  1. Installing an ECCO PE400 root-resistant layer, if necessary. A root-resistant sheet is not always required in case of EPDM or PVC, unless expressly instructed by the manufacturer.
  2. Installing the ECCOprotect 400 protective layer: these 2.10 m x 40 m rolls are installed with 10 cm overlaps. These rolls are available by the m².
  3. Installing the ECCOsedum green roof trays: the green roof trays are held together by a click system and are cut using a saw or a grinding disc. The RHP substrate is held together by the roots of the sedum plants. When cutting, do try to keep the water buffering layer intact by cutting only to half height.
  4. Vegetation-free zone: In case of more elevated roofs, we advise against having the ECCOsedum trays reach to the roof edges (vegetation-free zone of +/- 30 cm). This area is then filled with roof gravel, preferably 40 -80 mm. Finer fractions are not recommended in order to prevent weed growth. This vegetation-free zone has multiple purposes:
    preventing splashing precipitation from soiling the adjacent building
    protecting the water drainage against clogging as a result of ingrowing vegetation
    preventing the vegetation from hanging over the eaves
    preventing any outbreak of fire from spreading from/to the vegetation
    preventing the vegetation layer or substrate from being blown away by wind forces
    preventing the wind from blowing up the sides of the ECCOsedum trays
  5. Cutting the sedum tray, if necessary: only cut the top layer, keeping the bottom layer (water-buffering layer) intact.

The ECCOsedum green roof system consists of 3 layers:

  1. Drainage layer: The trays have a structure designed in such a way that rainwater that cannot be absorbed by the green roof system can drain away without obstruction to the drainage points. The lower drainage holes are 1cm from the bottom so that even non-capillary water can be stored to a limited extent.
  2. Substrate layer – water buffering layer: The cassettes are filled with substrate up to full height (8cm). In some places (at the level of the emergency spillways) the thickness of the substrate is 3.5cm. The minimum thickness of the substrate is therefore 3.5 cm - the average thickness is 6 cm. The substrate layer has several functions. It provides nutrition and water for the vegetation and provides oxygen and anchoring of the roots. ECCOsedum uses a roof garden substrate, composed of lava, pumice and green compost.
    Volume of water buffering per tray: 32.5 litre/m²
    Granularity: 0-12mm
    Volume weight of substrate after compaction in dry state: 0.78g/cm³
    Volume weight of substrate after compaction at maximum water capacity: 1.27g/cm³
  3. Vegetation layer: The pre-cultivated extensive green roof system is supplied with at least 7 species of sedum plants per m². The cassettes are at least 80% full-grown upon delivery.
  • Our sedum trays are pre-cultivated to 80 - 85%. This gives you immediate results and we can call it a ready-to-use system. With a traditional construction, substrate layers and sedum cuttings/sedum mats are used, which always need a certain period of time to root and grow dense. This gives weeds the chance to grow in the green roof.
  • The sedum trays are very easy to install and it can be done by one person, which ensures a very fast and efficient installation. In a classical construction, blowing carts or big bags are used.
  • Since trays are used, they can be removed very easily in the event of any roof work after installation. With the classic system, the entire substrate layer must be removed and everything must be installed again afterwards.
  • The trays ensure a constant substrate thickness. With classic systems, the thickness of the substrate can vary between 1 and 8 cm, which also leads to weed growth.
  • In roofs with a slope, the substrate remains in the cassette. With the classic system, there is a risk of shearing and weed growth at the lowest point of the slope, as the moisture sinks to the lowest level and thus encourages weed growth.