Decisive for greening success - our substrate concept!
Competence and expertise in substrates for extensive and intensive green roofs
The substrate or vegetation support layer is a carrier medium and breeding ground for the plants. As a rule, "technical substrates" are used for green roofs and not locally available topsoils. These are usually too heavy, too loamy and generally have too high a proportion of seeds and roots of undesirable plants. It is possible to prepare locally available soils for use on the roof, but this is usually very costly.
Green roof substrates are mixtures of various components such as:
- lava
- pumice
- expanded shale
- expanded clay
- Brick chippings
- bark humus
- green waste compost.
Substrates for green roofs made from recycled aggregates are possible and are often used in practice. However, the current Fertilizer Ordinance, which regulates the use of recycled materials, and the RAL quality assurance for composts must be observed. However, when using composts, for example, it cannot be completely ruled out that unwanted foreign substances such as plastics, metals and glass may end up on the roof. The green roof guidelines specify limit values for these foreign substances.
Roof substrates are mixed and filled in earthworks as loose goods, in sacks, in "big bags" (plastic fabric sacks with a capacity of one to two cubic meters) or in silo trucks (pneumatic conveying technology). Substrates for green roofs are characterized by their low weight, high water capacity, good water permeability and sufficient air void volume.
There are also suitable substrates for extensive and intensive green roofs for different applications, including
- Extensive single-layer substrate
- Extensive multi-layer substrate
- Intensive single-layer substrate
- Intensive multi-layer substrate
- Light substrate
- Turf substrate
- Sub-substrate
Once the vegetation objective is clear, the appropriate green roof substrate and drainage layer can be selected. The quality criteria for substrates are the parameters of the green roof guidelines. Particular attention should be paid to the maximum water capacity, air void volume, water permeability and nutrients.
Proportions of organic substances promote vegetation development
A certain proportion of organic matter (bark humus, compost and other peat substitutes) in the substrate for both extensive and intensive green roofs is desirable and beneficial to vegetation development due to the nutrient supply and buffering functions. Mineral substrates with the addition of zeolites (clay minerals) have proved particularly effective when combining green roofs with the use of service water in order to keep the excess water from the green roof as colorless as possible.
Possible sources of error with substrates
Choosing the wrong substrate can not only mean that the plants do not grow, but even worse, that excess water does not drain away and increased loads are placed on the roof. The following possible sources of error should be considered with green roof substrates:
- Lack of water permeability
If the proportion of fines in the roof substrate is too high, the excess water cannot be drained quickly within the substrate and accumulates on the substrate surface. - Insufficient water retention capacity
If the material in the substrate is too coarse-grained without fine particles, the water can hardly be retained and the green roof substrate dries out quickly. This is much more pronounced with closed-pored material. - Lack of grain grading
Substrates with a lack of grain grading either lack water retention capacity or water permeability. Single-grain substrates are unsuitable. - Organic content too high or too low
Too much organic matter in the substrate leads to heavy subsidence and an excessively high nutrient content. Roof substrates with a (high) organic content should only be used up to a height of around 35 cm; a mineral substrate should also be used for higher green roof layer structures. Low or no organic content reduces the water retention capacity and nutrient supply. - Use of untested aggregates and mixtures
Non-quality assured composts in the substrate inhibit the growth of vegetation due to nutrient fixation.
A recipe for success - the Optigreen substrate concept
A good green roof system provider is characterized above all by its expertise and specialist knowledge of substrates for extensive and intensive green roofs, as these are ultimately decisive for the success of the green roof. The substrates for extensive and intensive green roofs from Optigrün international AG are ideally matched to the various green roof system structures. Only the right substrate guarantees the functionality of the green roof. Optigrün can look back on a great deal of experience in development and in practice:
Optigrün developed and used the first substrates for green roofs back in the mid-seventies of the last century. The green roof market has continued to develop - new construction methods have been added, requirements have changed and customers expect top quality at reasonable prices. The purpose of the Optigrün substrate concept is to provide the right, cheapest and most readily available substrate for the desired area of application. In addition, the transport routes for the roof substrates and thus the CO2 emissions are to be minimized. This is made possible by a network of substrate production sites in Germany and Austria, which produce substrates according to Optigrün international AG recipes.
The substrate recipe depends on the correct combination of locally available raw materials. The quality of an Optigrün substrate is based on the parameters specified by Optigrün international AG. Our substrates are optimally matched to our system structures and thus guarantee a long service life of the system. All substrates comply with the FLL green roof guidelines, ÖNORM L 1131 in Austria and the Fertilizer Ordinance.
Optigrün has been offering tried-and-tested and permanently functional basic, supplementary and special substrates for many years, which are characterized by the following features:
- Reliable drainage and high stability of the plants thanks to a high proportion of interlocking mineral stabilizers
- Permanent air void volume for optimum root penetration and species-appropriate growth thanks to good grain grading
- High nutrient and water storage capacity with good water permeability
- Tread stability
- Use of pollutant-free, natural aggregates of mineral and organic origin
- Tested recycled materials from selected suppliers
- Material logistics tailored to the construction site
The following delivery forms are available for Optigrün substrates:
- loose poured
- Big bag 1.0-2.0 m3
- blown in a silo truck
- Bagged goods in 25 and 40 liter bags
The logistics of the substrates to and on the roof must also be right. Whether at a height of 50 meters, at a distance of 120 meters or in a courtyard situation. Not every substrate is suitable for blowing onto the roof. The substrate formulations must therefore be adapted not only to the use of plants, but also to logistical requirements such as "blowability". Optigrün has been working for years with logistics partners who are able to reliably transport the required material to the property and onto the roof.
Optigreen base substrates
The distinction between "light" and "heavy" only applies to Optigrün base substrates and refers to the weight of the finished substrate mixture. The required characteristic values of the green roof guideline and the Optigrün requirement profile are complied with for both light and heavy substrates. Light and heavy substrates for extensive and intensive green roofs differ in appearance, due to the different aggregates and weight. The "light" substrates consist of light aggregates such as expanded shale, expanded clay and pumice. The "heavy" substrates, on the other hand, contain heavier components such as lava etc.
The following Optigreen basic substrates are suitable for "classic" extensive and intensive greening:
- Optigreen extensive single-layer substrate M ("l" light and "s" heavy)
For extensively greened flat roofs in single-layer construction with limited plant diversity (mainly Sedum species). Predominantly mineral components, low proportion of organic matter. Combines drainage and vegetation base layer.
More about Extensive single-layer substrate light M/l
More about Extensive single-layer substrate heavy M/s - Optigreen extensive multi-layer substrate E ("l" light and "s" heavy)
This substrate is suitable for extensive green roofs in multi-layer construction (with additional drainage layer) with medium to high Pflance diversity. For extensively greened pitched roofs in single-layer construction with medium to high plant diversity. Predominantly mineral components, but with a higher organic content than the Optigreen extensive single-layer substrate type M and with a higher maximum water capacity.
More about the extensive multi-layer substrate light E/l
More about the extensive multi-layer substrate heavy E/s - Optigreen turf substrate R
This substrate is ideal for a well-maintained and walkable lawn for intensive greening. It has a high maximum water capacity with increased permeability and is tread-resistant thanks to its good interlocking properties.
More about Optigreen turf substrate R - Optigreen intensive substrate i ("l" light and "s" heavy)
For intensive greening in multi-layer construction (with additional drainage layer) with a wide range of suitability and a varied selection of plants (perennials and shrubs). High maximum water capacity. Organic substance for nutrient storage and buffering capacity. Also suitable for outdoor planters.
More about intensive substrate i/l
More about intensive substrate i/s - Optigreen sub-substrate U ("l" light and "s" heavy)
Lower vegetation layer ("subsoil") to be covered with Optigreen intensive or turf substrate. This substrate improves the stability of shrubs and trees. It also promotes root respiration and root penetration into deeper layers due to its very low organic matter content, thus counteracting undesirable rotting processes.
More about Optigreen sub-substrate U/l
More about Optigreen substrate U/s
Optigreen supplementary substrates and special substrates
Optigreen supplementary substrates are used for green roofs with special requirements. These substrates supplement the basic substrates with regard to special requirements such as lawns with and without trafficability and light extensive construction. The respective suitability should be agreed with the Optigrün application technology staff.
- Optigreen lightweight substrate L
For single-layer extensively greened flat roofs based on the LEICHTDACH system. Very light substrate with high water storage capacity. It consists exclusively of mineral components. Optigreen lightweight substrate L can only be used in conjunction with vegetation mats.
More about Optigreen lightweight substrate L
Optigreen special substrates are used for green roofs with special requirements Their product properties make these substrates absolute specialists, which are only used in special installation situations and thus complete our substrate range.
- Optigreen Optilith
Mineral substrate with zeolites to improve nutrient capacity and reduce water turbidity. Optilith contains no organic substances and is particularly suitable for green roofs with downstream service water utilization in combination with a cistern for toilet flushing or garden irrigation.
More about Optigreen Optilith - Optigreen Urban Soil US
Ideal for urban gardening and urban farming projects or the Optigrün URBAN GARDENING system structure, suitable for growing vegetables and fruit. Basic substrate that can be fertilized as required.
More about Optigrün Urban Soil US
Why excavated soil should not be used
Many years of practical experience have shown that local excavated soil can only be used in exceptional cases and not without extensive modifications and analyses. The following reasons speak against the use of excavated soil on the roof:
- Weight
At around 2,000 kg/m³, soils sometimes weigh twice as much as special roof substrates. - Unwanted foreign growth
Regenerative root and rhizome pieces, shoots and seeds are applied with the soil and can only be removed later (if at all) with increased cleaning effort. - Water permeability
Clayey and loamy soils in particular have a water permeability that does not meet the requirements of the green roof guidelines. This results in waterlogging and an uneven supply of water to the vegetation. - Fines
Washed-out fines can clog the filter fleece, which can lead to waterlogging. - Logistics
As a rule, local soils cannot be blown, i.e. the usual "blowing" onto the roof is not possible. Other, possibly more expensive application methods must be selected. - Topsoil that is too fine
This results in a lack of water permeability. - Extraneous growth due to root pieces and seeds in the topsoil
Conclusion on substrates for extensive and intensive green roofs
The right substrate selection for extensive and intensive green roofs is crucial and depends primarily on the vegetation objective. Based on the client's vegetation requirements, the planner must determine the appropriate green roof layer structure (single or multi-layer, extensive or intensive) and the corresponding substrate. It has proven to be a good idea to use tested brand substrates that comply with current guidelines and standards and are also backed up by property-related consulting services and system structures.
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- Technical brochure (pdf) 11 MB