Construction Management & Sustainability Research Shadyside Giant Eagle Green Roof Project

Green Roofs

A complex layered roofing system makes up the typical green roof. A layer of waterproofing is the first component placed on top of the roof deck. With the task of keeping the structure dry, this is perhaps the most important layer. Next is a drainage layer, which functions to carry excess water off the roof and stores water for the plants. On top of this is a filter fabric that prevents soil particles from washing away. The growing medium, typically a lightweight soil-less mix follows, with the plants capping off the green roof.

There are two basic types of green roofs: extensive and intensive. This project focuses on extensive green roofs. They are usually built for their environmental benefits and are low maintenance. The growing medium is a few inches thick, usually no more than six. Low lying ground cover plants blanket the roof. Sedum is one of the most popular types of plants for use in extensive green roofs. The ground cover plants are chosen for the specific climate and are meant to survive on the natural rainfall. The maintenance is normally limited to a few trips to pull weeds. Extensive green roofs are fairly light and are not designed to carry the live loads of visitors, so they can be retrofitted to old buildings. Intensive green roofs, on the other hand, are quite heavy and are designed to for live loads. They are essentially roof top parks. As such, they contain many large trees and shrubs that require growing media depths of up to several feet. Intensive green roofs are mainly constructed to bring green space into cities, rather than to reap the environmental benefits.

Benefits

The environmental benefits of green roofs fit into two main categories: water and temperature. The plants and soil on a green roof are able to absorb rainwater, reducing stormwater runoff. This is especially important in Pittsburgh, where hundreds of Combined Sewer Overflows (CSOs) release raw sewage into the city's rivers each time it rains. As urban sprawl has increased the amount of impervious surfaces in Pittsburgh (and many other cities), stormwater runoff levels have spiked. The old sewer system simply can not carry the load, resulting in CSOs. Green roofs can be part of an overall regional plan to solve this problem. Since water must first filter through the growing medium, green roofs also reduce the rate that runoff reaches the sewer system. Additionally, the plants and soil in green roofs have been shown to absorb pollutants, like metals and nitrogen, which are typically found in runoff.

Concrete and asphalt are common materials in modern cities. They absorb heat during the day that is then released at night. This prevents cities from cooling down at night. As a result, cities are often several degrees warmer than the surrounding countryside. By replacing standard building materials with plants and soil, green roofs break this cycle. Green roofs also act as a layer of insulation. This reduces cooling costs in the summer and heating costs in the winter.

Green Roof Project

• Project Background
• Project Information
• Additional Project Information
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