Green Roofs: More than Meets the Eye
The grass isn’t always greener in your front lawn. With the growing awareness of global warming Americans are becoming increasingly ecological, and breathing new life into the term eco-friendly. Environmentally conscious consumers are finding more creative ways to go green – and now they’ve found a way to raise green turf to new heights.
A green roof is much more than, well…green. A green or vegetated roof refers to a roof that is partially or completely covered with vegetation and soil, or a growing medium that is planted over a water proof membrane. It often includes additional layers like root barriers, drainage, and irrigation systems…OK, it’s a lawn. That’s right, a lawn that can lower your energy bill, lower greenhouse gas emissions, reduce storm-water runoff, lower your stress level, and provide a habitat for surrounding wildlife.
We can give Germany credit for giving us more than just good beer and Beethoven. They also modernized green roofs, which have actually been around for centuries in Northern Scandinavia. Now, about 10% of all German roofs have been “greenified” and the trend has spread throughout Europe. Although vegetated roofs aren’t nearly as common in America as they are in Europe, it is becoming a more and more popular way for people to green their homes – literally.
· Choose the right roof - There are two main types of green roofs. Which you choose is dependent upon many factors such as the intended purpose of the roof, the type of building, your budget, etc.
· Intensive (garden-style) - Intensive roofs resemble gardens or parks. They are often used on flat roof-tops in large cities where park space is limited. Intensive roofs usually require about 6-24 inches of soil that is able to grow shrubs, small trees, lawns, even vegetable gardens. These garden-style rooftops may raise the bar when it comes to backyard barbeques and prove to be the lawn of the future. Consult a green roof specialist before considering installation of an intensive roof because they may require more sophisticated structural support and irrigation.
· Extensive (lawn-style) - Extensive roofs are the most common type of vegetated roof for a home because they require low to no-maintenance. An extensive green roof only requires a very thin layer of soil (1-6 inches), and can sustain many different types of grass. It is virtually self-sustaining and only requires weeding about once a year. There is usually no access to an extensive roof except for what is necessary for maintenance. That means no roof-top barbeques. Since extensive roofs support drought-resistant, shallow-rooted plants, and grass which generally grows no higher than a few inches (which means no mowing) they are ideal for homeowners looking for an easy way to save on energy consumption and make their homes more eco-friendly.
· Cost – Green roofs can cost around $10 - $15/sq. ft. for extensive green roofs and anywhere between $25 - $100/sq. ft. for intensive roofs. Of course the price depends on the geographic location, type and intent of the roof, installer, etc. A park complete with trees, walkways, and vegetable gardens is going to cost quite a bit more than a simple grass lawn. Either choice, however, will prove to be an economical and ecological benefit in the long run. Below are a few areas where a green roof can save you money.
· Maintenance – The sun can break down roofing materials over time requiring costly replacement and rebuilding. It is recommended that a conventional asphalt roof receive maintenance every 2 years, which could total up to $1,300 for a 2,500/sq. ft. roof that is about 1-5 years old (older roofs would cost more). The vegetation on a green roof acts as a barrier protecting the roof from harsh solar rays and protecting your wallet from the expense of constantly replacing worn roofing materials.
· Heating – You can save energy in cooler months with green roofs because they provide excellent insulation and retain 18% more heat than conventional roofs.
· Cooling – The temperature of a conventional roof membrane on a 95º F day can rise up to 158° F. The temperature of a green roof on the same day is about 77° F. A cooler roof means lower cooling costs in the summer.
· Structure – Because of their weight, green roofs require more demanding structural standards than regular roofs. Depending on your house, roof, and the type of vegetation you plan to install, structural reinforcements may be needed. Choose a quality service provider who will inspect your home properly before installing a green roof. Check your local listings or visit the Green Pages at www.sierraclubgreenhome.com for a list of reputable green roof installers.
· Grass, shrubbery, and flowers obviously make vegetated roofs more aesthetically pleasing; and if your home is a little bare when it comes to front yard space, a green roof is a great way to show off your gardening skills.
· Studies show that visual and physical contact with natural greenery provides both mental and physical health benefits such as: lower blood-pressure, lower heart rate, reduced stress or mental fatigue, assistance in quicker recovery from physical illness, and they provide long-term overall improvement in health. The health advantages of vegetated roofs are beginning to grow on many hospitals and health facilities, who are installing them for the benefit of recovering patients. For more information on studies regarding the health benefits of green surroundings visit http://www.naturalnews.com/025260_health_greenery_health_benefits.html.
…to your wallet
· A 2006 study by the University of Michigan comparing expected costs of conventional and green roofs revealed that, on average, installing a green roof costs about $22.10/sq. ft. versus $15.95/sq. ft. for a conventional roof. In its life, however, the green roof saves over $200,000 with two-thirds of that coming from reduced energy needs. Taking into consideration the added savings, the average cost of this topnotch turf would be about $12.57/sq. ft. - meaning you could save $3.38/sq. ft. by choosing a green roof.
…to the earth
· Green roofs are able to make much better use of rainwater than conventional roofs. A green roof can capture precipitation and influence it in 3 ways:
1) Taken up by the plants
2) Absorbed into pore spaces
3) Stored and retained by the drainage system of the roof
If the water is not absorbed by the vegetation, it is stored in other layers of the roof, and can be released back into the atmosphere rather than simply running off into a drainage system. Basically, green roofs reduce the amount of water that is wasted when it ends up in drainage systems.
· Lowering air-conditioning demand decreases the associated air pollution and greenhouse emissions. The vegetation can also remove air pollutants and greenhouse gas emissions through dry deposition and carbon sequestration and storage. According to one website, a square foot of vegetation absorbs about 0.33 ounces of air pollution per year, so a mere 1,500 sq./ft. vegetated roof could absorb over 40 pounds of air pollution each year and almost 2,000 pounds in its lifetime. The impact of green roofs on large commercial buildings is obviously even greater.
· The first step to installing a green roof is contacting a roofing specialist or architect to ensure your roof is sufficiently structurally sound. Use this link to guide you in selecting the proper professional: “What to Ask Your Contractor” .
Planting Green Roofs and Living Walls by Nigel Dunnett and Noel Kingsbury