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MythBusters
Well, no and yes. The requirement for irrigation will depend on the climate and the type of vegetation that must be supported. In many regions of the United States and Canada, green roofs can be readily designed without irrigation. Only 15% of currently installed Roofmeadow® green roofs are irrigated. The un-irrigated assemblies are succeeding very well. However, compromises are often required in order to achieve this outcome. Compromise 1: Be patient. Green roofs installed without irrigation may take longer to reach maturity. However, when they do, the plants will be well adapted to their environment and highly resilient to climatic variations. The foliage on some roofs may require 2 to 3 years to fill in completely. This process can be accelerated by temporary watering, but even temporary watering is not required in most regions. Importantly, installation contracts should include provisions for the installation contractor to maintain the green roof during the establishment period. Additionally, criteria for final cover acceptance also should be part of the contract. Compromise 2: Limit the plant selection. The plants that are heat tolerant and adapted to drought conditions in a particular region may be limited in number. Most of these plants will not be North American natives. However, the list of plant species appropriate for different regions and circumstances is always being enlarged through experience with green roof installations in the United States. Compromise 3: Use water-retentive mineral media. As a general rule, green roof media that contains large percentages of organic matter (coir, peat moss, shredded bark, root mulch, etc) will require frequent irrigation during drought conditions. Long experience has shown that mineral media that contains a high surface area and water absorptive properties will offer the best protection against drought. In many cases, mineral media will not add any more weight than organic-rich media to a green roof because many organic-rich materials become very heavy when they are saturated and compressed. For more information on media properties and plant selection consult our FAQs
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MYTH 1: Irrigation is essential for green roof success