Vegetative roofing systems are a combined assembly and need to be addressed as such. The waterproofing membrane that keeps the building dry is one component, and the growing media and plantings are another. Systems are typically classified as intensive or extensive.
Intensive systems have about 3 feet of soil or growing media for planting lawns, heavy shrubs, trees, and other plantings with large root structures. These systems require a structure that can support the additional weight of the vegetative system. To ensure a leak-proof project for intensive systems, managers need to pay special attention to waterproofing design and monitor system installation closely. Locating and repairing leaks on an intensive vegetative roofing assembly can be time-consuming and expensive.
Extensive vegetative roofing systems have a much thinner layer of growing media — typically, about 6 inches. These systems do not allow the same variety of plantings as intensive systems because the plants' root structures must be shallower. Organizations can install extensive systems on more types of buildings because they are much lighter, and the structural requirements to support them are less demanding.
The newest entrants into the vegetative roof market are prepackaged trays with seedlings or mature plants that lay over the waterproofing and protection system. Extensive systems are effective for providing a vegetative system at a much lower cost and require less work to install and maintain than intensive systems.
Whether a manager chooses an intensive or extensive system, protection mats and root barriers laid over the waterproofing membrane are important elements of a well-designed system.
Vegetative Roofs Moderate Interior Building Temperatures
Vegetative Roofs: How to Ensure a Leak-Proof System
Vegetative Roofs: Pay Attention to Structure, Plants, Rooftop Access
Vegetative Roofs: How to Waterproof the System