Many cities have mandated increased energy efficiency in buildings and, in some cases, net zero energy use by buildings. A variety of solutions is needed to meet these goals; some are cutting-edge digital technologies, while others have been around for thousands of years. Green roofs, one of the oldest energy-saving technologies, are becoming increasingly popular and having an impact on sustainability efforts.
Modern green roofs employ advanced design and materials to provide residents with rooftop oases while saving energy. There are two primary types of green roofs: extensive green roofs, which generally have 2 to 12 cm of planting medium and are designed to be virtually self-sustaining; and intensive green roofs, which are far more complex and act as rooftop parks and gardens. Intensive green roofs have soil depths of more than 12 cm and can include shrubs, small trees, and conventional lawns. Given the amount of materials and the additional weight required for intensive designs, they are not suitable for all roofs. Companies such as Illinois-based TectaGreen have been installing various types of green roofs on buildings across the United States for many years.
Cool Under Cover
Green roofs have been used for centuries to provide insulation and protect roofing materials, and they provide many benefits to building owners, occupants, and the general public. Rooftop vegetation offers several public benefits; it improves urban air quality, manages stormwater runoff, and helps moderate the urban heat-island effect. But it’s the private benefits for building owners that are primarily driving the market for green roofs.
The most direct benefit is reducing the amount of energy required to heat and cool buildings. Several studies have shown that installing a green roof reduces summer cooling needs and winter heat loss by as much as 26%. Green roofing can also extend the lifespan of a roof by protecting the waterproofing membrane from ultraviolet radiation and physical damage. Other benefits include noise reduction, the reduction of electromagnetic radiation, and compliance with building codes such as Leadership in Energy and Environmental Design (LEED).
Small but Growing
While costs for green roofs have dropped in recent years, there is an ongoing debate over their cost-effectiveness and payback period. Installed costs of green roof systems can vary dramatically; extensive roofs (shallower) generally cost from $10 to $23 per square foot to install. Intensive roofs can cost anywhere from $25 to $220 per square foot and may require regular maintenance. Some argue that at those prices, green roofs cannot pay back their installation costs. But it can also be argued that the most important benefits are those that are not easily quantified. What’s more, compared to other, more intrusive energy efficiency measures, green roofs are relatively inexpensive.
Despite the cost, green roofs continue to be installed around the world. Navigant Research’s recent Zero Energy Buildings report discusses the efforts underway to lower building energy consumption; green roofs represent a small but growing part of that effort. In addition to energy efficiency, green roofs are part of a growing movement to improve the sustainability of urban environments and reconnect residents with the natural environment that their cities have largely erased. They are sure to grow in popularity over the coming years.