Living Roofs
A living green roof, in which a system of living plants and vegetation is installed onto the roof of a structure, has many environmental benefits, and can be a beautiful visual representation of your desire to protect our earth's natural resources.
Green roofs are nothing new; the use of layers of living material to provide shelter and insulation for structures has been around since the earliest days of human civilization.
Green roofing systems have been popular in Europe for decades, from simple sod roofs to more modern systems. Dramatic improvements in green roofing designs and technologies are making them available and viable for use in almost all climates and areas of the U.S.
Types of Living Roofs
There are two basic types of green roof systems, extensive and intensive.
An extensive system uses low-lying plants such as sedum, moss, and grass in thin layers of soil. Extensive systems weigh between 10 to 50 pounds per square foot on average. Extensive systems are the most common type of green roof system for residential applications.
The other type, intensive, uses deeper soils and larger plants, including trees and shrubs. Intensive systems are much heavier than extensive systems, and can be harder to maintain. For our purposes, we will concentrate on the extensive green roof systems.
Green roofing systems can use a variety of materials. Growing mediums can be soil, peat, gravel, or other organic materials. A layer for drainage is needed to distribute moisture to the living material, and are usually made from rubber or plastic. An important component of the system is a waterproofing membrane to keep moisture from penetrating the underlying roofing.
Plant Requirements for Living Roofs
Just like the materials used in shingles or other roofing materials, plants in a green roof system must be tolerant of extreme temperatures, from hot sun to freezing cold to periods of drought. Rooftop plants should also be low maintenance, have shallow root systems, and relatively resistant to insects and disease. The easier the plant is to maintain, the less time you'll need to spend up on the roof caring for them.
There are many types of climate-appropriate plants, from succulents to sedum to mosses and grasses that will thrive in a rooftop environment. Today's green roof plants are available in a variety of colors, and there are nurseries countrywide that specialize in these green roof plants.
Environmental Benefits of Living Roofs
A green roof on a home has several important ecological benefits:
- Green living roofs have an added mass and thermal resistance, which reduces the heating and cooling costs for a home. A green roof reduces the ambient temperature around the roof, which in turn will slow and reduce the transfer of heat into the living space below. The mass of a green living roof adds insulation to the roof, reducing heat loss through the loss during colder months, reducing heating costs.
- A living roof greatly reduces water runoff during rain, by absorbing and retaining water in the soil medium, which the plants use for growth. Stormwater runoff from hard surfaces such as roofs are a large contributor to water pollution in rivers and streams. A study on green roofs in Seattle found that green roofs reduced rainwater runoff from 65 to 94 percent.
- Living roof plants can filter pollutants and carbon dioxide from the air and water, and can serve as a habitat for birds and other wildlife.
- A green, living roof shelters the roof from extreme temperatures, UV radiation, and other harsh conditions, which extends the life of the roof, in addition to the reduction of energy usage and costs.
Installing Living Roofs
A living roof can be added to a new or existing roof. Due to the increased weight of a green roof, it is important to consider the structural design of the home to make sure it will support the roofing materials. It's also important to make sure the right roofing system is chosen for a roof's slope, and that the appropriate roof plants are used for the home's climate region.
Living Roofs: How Much Green Will It Cost?
There's no getting around the fact that a green living roof will cost more than a traditional roof such as asphalt shingles. Up front costs associated with design, research, and installing the roof system and structural support can contribute to an overall cost for extensive green roof systems of anywhere from $7 to $15 per square foot.
Maintaining the plants on a green roof also has some additional costs, but overall costs may be lower, since the roofing membrane maintenance is minimal, and planted roof systems typically increase the life of the roof, keeping repairs and replacement costs down. That, coupled with the savings in energy costs associated with a green roof, make a living roof a viable option for any green home design.
Green Home Source endorses the Hortech LiveRoof System as our preferred living roof system. To learn more about LiveRoof, click here.
Visit our article about the Ford Rouge Factory and see what a fantastic job they did intetrating a live roof into the facility.
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