A subtropical climate vegetated roof (SCV roof) is a type of green building practice that employs a planted soil media installed above a waterproof roof deck to obtain environmental benefits and address sustainability concerns, similar to traditional green roofs located in northern continental United States. Soil media, plant palettes, and green roof systems that can adapt to the adverse weather conditions and physical characteristics of the humid, subtropical regions of the United States are utilized in the construction and design of subtropical climate vegetated roofs. Green roofs are used for various reasons including: urban oasis, storm water mitigation, carbon reduction, energy conservation, aesthetics, and therapeutic values depending on the geographic location and the intended specific goals of the project. Most of the current green roof research pertains to northern parts of the continental United States, whereas, very limited research has been conducted in humid, subtropical regions. Although similar characteristics and principles exist, there are several differences between the two types of environmentally sound roofing systems. These differences are comparable to the differences found between regions of the United States in conventional landscaping and gardening or the variations found in forms of landscaping. Plant species and landscaping methods utilized in northern parts of the United States are not suitable for humid, subtropical regions of United States due to the extreme temperatures and rain events that occur. This accounts for the most significant difference between a green roof in northern United States and a subtropical climate vegetated roof (SCV roof). A subtropical climate vegetated roof that is well designed according to the specific geographic locations climate can lower roof surface temperatures by as much 38° and depending on the amount of the event retain up to 88% of rainfall. An improperly designed subtropical climate vegetated (SCV roof) using incorrect soil media and plant species can fail by not achieving the intended goals. This roofing method also contributes towards growing the green economy, sustainable energy technology policies, and qualifies for Federal and local tax incentives, set in place by the United States government.
Technology and terminology Compared with other parts of the United States, the number of vegetated roofs currently in the Southeast is significantly less. Vegetated roofs in humid subtropical regions rely on the same core green roof terminologies that are used throughout the world and other parts of the United States. Extensive, intensive, soil media, ballast, filter fabric, drainage layer, waterproof membrane are some of the core green roof component terms associated with SCV roofs. Regional terms, plant palettes, and technologies are forming to adapt to recent innovations and increased popularity of green roofs in the humid, subtropical regions of the United States. All forms of green roofs have the potential to retain stormwater on the roof surface and lower the thermal loading on buildings. Due to high temperatures, prolonged heat, and excessive amounts of precipitation, humid subtropical regions of the United States receive the greatest environmental benefits provided by SCV roofs, which are: reduced rainwater input into storm water retention systems during rainfall and increased energy performance ratings in buildings. SCV and green roofs increase energy efficiencies of buildings by stabilizing roof surface temperatures. In other regions of the United States, the greatest environmental benefits of green roof design may be different based upon the type of climate the area possesses. Recent advancements in soil engineering and plastic technologies allow vegetated roofs the ability to adapt to different locations within the humid, subtropical region of the United States. Soil media moisture content and capacity levels can be regulated by using soil elements that adapt to the climate of each specific geographic location and client needs. The amount of moisture retained depends on the maximum moisture retention capacity, the permeability and the depth of the soil media. High density plastics permit SCV roof systems to withstand the weather elements and adjust to varying building types of the region. As defined by green roof industry standards, extensive green roofs have a soil media of less than 6 inches in depth and intensive green roofs have a soil media of more than 6 inches in depth. Most SCV roofs that are greater than 6 inches in depth are expensive and found on residential high rise structures, often containing pools and other amenities. An SCV roofs requires a unique soil media mixture to adapt to the harsh weather conditions and physical characteristics of the southern United States. Expanded shall and clay are typically used to form a base and comprise up to 90% of some soil media mixtures used throughout the United States. Perlite, vermiculite, ash, tire crumbs, sand, peat moss, and recycled vegetation are some of the other elements utilized in soil media engineering. Albedo and heat transfer rates are key variables to consider when designing an SCV roof and do not have a significant effect on green roofs in the northern continental United States. There are three basic SCV and green roof systems available in today's market: built-up, modular, and mat. These systems vary from manufacture to manufacture and are composed of different materials such as: foam, high density plastic, and fabrics. Many of the systems have geographic limitations and do not perform well in humid, subtropical regions based upon the intent of the system and the materials being used.
Built-up Multi-layered systems containing the following functional layers: root barrier, protection layer, drainage layer, filter layer, growing medium and plant level.
Modular systems Self-contained units, typically square in shape, that require only the soil medium and vegetative layer for a functioning green roof. These systems are easy to install and remove. Some modular systems are pre-grown at nurseries to client specifications, forming an instant vegetative layer.
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