GREEN ROOFS
Photos: Meagan Henke
Introduction:
History:
Green Roofs have been a standard construction practice in many countries for hundreds, if not thousands of years. They have been historically used for their good insulative properties and some of the first Canadian examples can be seen in
Types of Green Roof Systems:
Green roofs can be categorized into two main systems outlined primarily by their design, construction requirements and guidelines. Intensive systems, as their name suggests, require more attention from the design, through to the construction and implementation as well as require more maintenance down the road. They do, however, provide higher benefits in terms of accessibility for users and increased opportunity for roof utilization. Extensive systems tend to be more advantageous in retrofit projects where roof loading is a main concern. Because of the more limited plant choices an extensive system is often considered unattractive, especially in winter.
Private Benefits:
The private owner can benefit from green roofs in many ways including their high insualtive properties, sound insulation, life extension of the roof and increased aesthetic appeal. The insulative properties of green roofs have considerable energy savings. Peck notes that a twenty-centimeter growing medium and a thick layer of plants has an insulative value comparable to that of R20 (2000, 6). This decreases the energy required to cool a building in the summer and heat it in the winter and translates to a cost savings for the building owner. Because a green roof is more protected against harmful ultraviolet rays and general damage its life can be extended up to two times that of a conventional roof. Decreasing the need for re-roofing a building is obviously a huge cost savings to its owner, but also decreases the amount of waste and landfill that would be required in re-roofing. Their durability can help to offset their high installation costs, which is usually the main barrier when considering a green roof.
Public Benefits:
Increasing the vegetation in an area increases the rate at which fine particulates are filtered out of the air. Air is filtered as it passes over the plants and through the growing medium and "studies show that treed urban streets have 10-15% fewer dust particles than found in similar streets without trees" (Peck 2000, 9). Green roofs help to produce oxygen and "assimilate excess carbon dioxide produced by city traffic and industry" (Birkeland 2002, 101). For those that may have health problems such as asthma, allergies or related respiratory problems, a healthier environment in terms of air quality will be of benefit to them personally as well as help to ease the burden of those types of illnesses on the healthcare system.
The reduction of available open ground-level green space in urban centers is a growing problem and addressing the roof is one way to relieve some of the negative impacts of higher density. Dealing with a roof top garden successfully can result in benefits including adding to the urban character of a neighborhood, social benefits, urban agriculture and habitat restoration. This gives
The Problem:
Although many private benefits of green roofs have been studied and proven, public benefits have had little impact on decision making due to the fact that they have not been incorporated into the market. The public benefits are not supported by sufficient technical data and therefore cannot be quantified in monetary terms and unfortunately that is often the bottom line. More research is needed to make a strong local case for public incentives to help stimulate private investment. Incentives and tax relief are needed to encourage businesses, government and users that green roofs are a viable option to obtain a higher quality of life in