Costs
A properly designed and installed green-roof system can cost 15 to 20 dollars per square foot as a total cost (with the average cost decreasing with a larger area), not including the roof's waterproof layers. In Europe, a well-designed and professionally installed fully integrated green roof can cost anywhere between 100 to 200 euros per square meter, depending on the kind of roof, the building structure, and which plants are used.
Some cost can also be attributed to maintenance. Extensive green roofs have low maintenance requirements but they are generally not maintenance free. German research has quantified the need to remove unwanted seedlings to approximately 6 seconds/m²/year. Maintenance of green roofs often includes fertilization to increase flowering and succulent plant cover. If aesthetics are not an issue, fertilization and maintenance are generally not needed. Extensive green roofs should only be fertilized with controlled-release fertilizers in order to avoid pollution of the storm water. Conventional fertilizers should never be used on extensive vegetated roofs. German studies have approximated the nutrient requirement of vegetated roofs to 5gN/m². It is also important to use a substrate that does not contain too many available nutrients. The FLL guidelines specify maximum-allowable nutrient content of substrates.
Read more about this topic: Green Roof
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