As commercial businesses become aware of their direct effect on the environment, an increasingly popular building management response has been the adoption of green roofing. Exchanging traditional roofing systems with vegetated materials, green roofs provide building owners and tenants with numerous ecological, technical and economic benefits.
Both functional and aesthetically appealing, Green Roofing (also referred to as Roof Gardens and Vegetative Roofing) improves the structure's energy efficiency while adding plant life in populated areas.
Green roofing: extensive or intensive.
Extensive (eco-roofs or low-profile) green roofs are composed of fewer layers and are therefore lighter and less expensive. Optimal for ecological benefits, extensive green roofs are not intended for foot traffic. The types of available vegetative materials are dependent upon the unique constraints of the environment and the engineering of the roofing system.
Alpine-type plants are generally the most flexible because they flourish well in environments with limited moisture, heavy winds, and seasonal frosts. Critical to the functionality, maintenance, and longevity, the supporting soil mixtures are mostly inorganic.
Intensive (high-profile) green roofs are the more expensive and elaborate roof gardens with a broader variety of plant material. Intensive green roofs require a stronger load capacity given that larger vegetative growth requires deeper rooting and heavier moisture saturation. Further, the required soil mixture generally requires more organic components to support the vegetation. Intensive green roofing also requires a commitment to investment in regular maintenance.
Both extensive and intensive green roofs require irrigation systems. Although simpler in design, extensive systems are just as vulnerable to drying out and the proliferation of weeds and undesired trees seedlings. Depending on the budget, irrigation systems vary in functionality and cost.
From drip systems, to solar powered active irrigation systems, to recycled rainwater systems, green roofs are obviously much more resource intensive than traditional roofing systems. Beyond irrigation, green roofs can be extremely flammable, therefore, an extinguishing response system should be engineered into the design.
Green roofs require a high quality waterproof singe-layer or built-up membrane with adequate drainage before any vegetative materials are applied. Although traditional roofing technologies (single-ply, BUR, etc.) have made significant advancements in recent years, green roofs shield them from the sun's ultraviolet rays, fluctuating temperatures, and mechanical damage. If maintained effectively, green roofs can yield a much longer life-cycle than traditional roof systems.
When designed and installed by experienced roofing professionals, green roofs can negate the "commercial" look of a building. Further, green roofing meets the objectives of many of the mandates to improve the air quality of cities by mitigating the effects of heat islands caused by ever increasing development. The benefits of a Green Roof have been demonstrated by the US Green Building Council's endorsement of these systems through the LEED® (Leadership in Energy Efficient Design) certification program. Virtually any flat or gently sloped roof can be transformed into a landscaped environment.
Are Live Roofs Cost-Competitive to Traditional Roofing Options?
The initial investment cost of an extensive green roof starts at $8 per square foot, which includes materials, preparation work and installation. In comparison, the cost of a traditional built-up roof starts at about $3, while cool roof membranes start at approximately $3 per square foot. However, with energy efficiencies, return on investment on a green roof is tantamount with that of a traditional roof.