Green Roofing Overview
A green roof is a roof that has media and vegetation planted above a roofing system. The different components and wide variety of benefits is dependant upon the type and complexity of the green roof system. There are two types of green roofs; intensive and extensive. Living roofs have a wide variety of environmental and financial benefits.
Intensive green roofs have a thicker media and can support a large variety of plants, small trees, and other vegetation. Intensive green roofs require a minimum of 4-6 inches of media. Intensive green roofs are typically more functional and accessible to the public and comparable to a park. Extensive systems, which have a thinner growing media, are usually made up of drought resistant grasses and sedums. Extensive systems typically have a maximum of 4-6 inches of substrate. Extensive systems are sometimes fragile although pathways can be constructed for accessibility.
Green Roofing Technical Systems
- Root Barrier: The root barrier acts as a protection obstruction, which prevents the roofing system from being damaged by roots.
- Protection Layer: The protection layer is a puncture resistant membrane that prevents the root barrier from being damaged when the green roof is installed. Certain protection layers also can absorb water and nutrients.
- Drainage Layer: The primary function of the drainage layer is to allow excess water to run off, and is often constructed with lightweight materials.
- Filter Layer: The filter layer segregates the plant and media from the drainage layer. The filter layer prevents the drainage layer from becoming clogged as well as retains important organic materials in the media that are needed for plant growth.
- Growth Media: The growing media is the substrate that sustains growth in the green roof. It is a mixture of inorganic (crushed clay, expanded slate) and soil with organic and mineral additives (humus, sand, lava, peat). The media must provide nutrient, water, and air supply to the vegetation as well as resist frost, wind, and maintain a specific pH-value. The composition of growing media can vary in order to help reach a specific goal, such as water retention, fire retardant, or insulation value.
- Plant level: The plant level contains different varieties of vegetation that are dependent upon the specific green roof project and location.
Green Roof Planting
The optional planting period is in the early spring (April-May) and early fall period (September-October). It is important when planting to provide enough water to support low precipitation periods. Planting periods should avoid cold weather and frost as it can damage vegetation. The plant selection strongly influences maintenance requirements.
The maintenance requirements of a living roof are dependant on the thickness of media and plant selection. An extensive green roof that contains sedums and grasses usually requires no maintenance unless a substantial drought occurs. Intensive green roofs require more maintenance, an irrigation systems or regular watering. The plant selection is particularly important when considering maintenance requirements. The protection layer provided by the green roof reduces traditional roof maintenance costs.
Green Roofing Environmental Benefits
Green roofs replace the vegetation area that was destroyed when the original building was built. A key benefit of green roofs is their ability to reduce storm water runoff. Large amounts of storm water runoff can increase flooding, erosion, and overflow our local sewer systems. Green roofs can absorb and retain large amounts of water and release the excess over a few hours. A green roof can provide a natural cooling effect by mimicking natural landscape, which in turn reduces the heat island effect. A heat island effect is created when a highly populated area such as a city has higher temperatures than surrounding areas due to the city’s retention of heat through buildings and pavement. Living roofs are also one of the most effective ways to make a workplace or facility environmentally friendly.
Green Roofing Financial Benefits
Living roofs have a large amount of financial benefits. Green roofs provide added insulation that can lower heating and cooling costs while also qualifying for LEED points. A living roof provides an additional protection layer to a roof system. Green roofs have a longer life span than standard roofs because the extra layer provided by a green roof protects the roof from ultraviolet radiation, large temperature fluctuations, and general wear and tear. Green roofs not only increase the property value of a building but also add a functional aesthetic focal point to the structure.
The Future of Green Roofing…
There are a number of barriers that slow the growth rate of green roofs projects in North America. Lack of awareness, high installation costs, government incentives, and limited research are all barriers that are slowly being addressed in North America. Research provided by Michigan State University’s Department of Horticulture states that approximately 12% of flat roofs in Germany are green and the industry is growing at a rapid rate. Green roofs are relatively new but becoming increasingly popular and will likely become popular in the future. Green roofs provide environmentally friendly building solutions and long-term benefits, and also present work opportunities for a wide variety of professions.
Related Articles & Information:
- Video: Ashbury College Green Roof Growing Media Distribution
- Green Roof Services Provided by Godfrey Roofing Inc.
- Higher Learning: Green Roofs with a Mission