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Basic Vegetative Green Roof Definitions:

Vegetative green roofs can be categorized as extensive, semi-intensive, or intensive, depending on the depth of growing medium, design, and the amount of maintenance they need:

Extensive vegetative green roofs, which are 6 inches or shallower and are frequently designed to satisfy specific engineering and performance goals. Extensive design typically gives the owner the highest benefit-to-cost ratio. In most climates, a properly designed Extensive vegetative green roof cover will provide a durable, low-maintenance system that can realize the many benefits that vegetative roofs have to offer. Extensive vegetative green roofs are designed to be virtually self-sustaining and should require only a minimum of maintenance: occasional weeding and a yearly application of slow-release fertilizer to boost growth. Extensive roofs are usually only accessed for maintenance.

Semi-Intensive vegetative green roofs, which we refer to as designed vegetative green roofs, have a level of design with regard to planting layout. Depth of growing medium is typically 6 to 20 inches and can be planted with a large variety of plants. These vegetative green roofs are considered semi-intensive due to the landscape design coupled with increased levels of maintenance: dedicated irrigation system (variable), annual fertilization, and advanced horticultural care. Semi-intensive roofs are often used as building amenities accessible to the occupants as an area to enjoy nature.

Intensive vegetative green roofs, which are often referred to as rooftop gardens, require a reasonable depth of growing medium to grow larger plants or even conventional lawns. Rooftop gardens are considered intensive because they are labor-intensive to construct and maintain: a dedicated irrigation system, continual fertilization, and overall advanced horticultural care are required. Intensive roofs are park-like amenities accessible to building occupants or the general public.

GreenGrid Functional Vegetative Green Roof (Extensive)

Typically installed on non-visible roof surfaces, this design style lends itself to those roofs designed to satisfy specific engineering and performance goals (stormwater management, energy conservation, etc.).

  • Functional or Extensive vegetative green roofs are well suited to roofs with little load-bearing capacity.
  • Applicable to the GreenGrid 4-inch depth. Where added loading is required, the 6-inch or 8-inch depths can be designed as functional vegetative green roofs.
  • Typically the least expensive vegetative green roof application.
  • Minimal maintenance is anticipated. Annual fertilization followed up by monthly weeding is recommended. Irrigating during extended droughts is strongly recommended.
  • The mineral substrate layer, containing little nutrients, is not very deep but is suitable for less demanding and low-growing plant communities.
  • Drought-tolerant plant communities, such as those found in dry mountain environments, coasts, semi-deserts, or dry meadows, are visibly adapted to the natural extremes of the local conditions and are preferred species.

Designed Vegetative Green Roofs (Semi-Intensive)

Typically installed on visible roof surfaces, this design style lends itself to those roofs designed to satisfy specific engineering and performance goals (stormwater management, energy conservation, etc.) yet have the added benefit of aesthetics to enrich the building’s outward views.

  • Designed or Semi-Intensive vegetative green roofs in terms of requirements fall in between Extensive and Intensive vegetative green roof systems.
  • Applicable to the GreenGrid 4-inch, 6-inch, and 8-inch module depths
  • Higher costs and more weight are the characteristics for the intermediate vegetative green roof.
  • More maintenance should be expected for a designed roof given the possible design options and varieties of plants that can be used.
  • Combinations of succulent ground covers, conventional perennials and grasses, and native forbs and grasses can be used. Using a deeper substrate level to achieve this allows for greater diversity possibilities for the space. Furthermore, diversity possibilities increase if an irrigation system is added.

Rooftop Gardens (Intensive)

Generally require a reasonable depth of soil (>6 inches) to grow larger plants or conventional lawns. They are considered "intensive" because they generally require a lot of labor to maintain the park-like design. Most will require irrigation systems, fertilization, and other horticultural care to maintain the garden design. Intensive roofs are accessible and often include areas of hardscape, structures, and other features that create beautiful gardens on the roof.

  • Rooftop Garden or Intensive vegetative green roofs are typically designed as usable spaces made up of lawn, perennials, bushes, and trees.
  • GreenGrid 6-inch or 8-inch option.
  • Hardscape, such as walkways, benches, playgrounds, or even ponds can be established as additional features on the roof
  • There are no limitations in design.
  • Higher level of maintenance; permanent irrigation and fertilization have to be ensured

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