4 FM quick reads on Green roofs
1. Green Roofs as Sustainable Design Possibilities
Green, or vegetative, roofs are becoming more popular as sustainable design components. These roofs have several advantages over more traditional options. They minimize heat islands, reduce runoff into storm-water drains, provide excellent insulating values, and provide a green space for vegetation in large cities with limited green spaces.
They also can have disadvantages. Maintenance crews require training to inspect and repair them. Reflective walkways need cleaning.
Also, vegetation requires watering and care. In some cases, a landscape contractor — who now must be trained in fall protection to work on the roof — can be a better option for this task.
To make inspections easier, managers should consider specifying a tray system. Consider the Boston Children's Museum, which has more than 6,400 square feet of green roof made up of trays that workers can remove easily when inspecting and maintaining the roof.
If a green roof is an appropriate choice for a project, it might be best to buy an extended warranty from the company that installs it to ensure vegetation grows properly. This tactic also will provide more incentive for providing a quality installation.
2. How Vegetative Roofs Extend Service Life
Plants, soil, and covered components of the system offer protection from the elements, including degradation by the sun's UV rays. By protecting the membrane, a vegetative roof can minimize cracks and splits due to the thermal cycle. In some areas of the country, a roof membrane surface that is exposed to the sun may reach temperatures above 160 degrees Fahrenheit during the day and drop below freezing that night. The resulting expansion and contraction wreaks havoc on the membrane. But with a vegetative roof, this can be minimized, reducing or even eliminating one of the main causes of roof leaks.
As much as a 200-300 percent extension of roof membrane service life may be achieved with the use of vegetative roofing. This is backed by the availability of manufacturers' warranties for as long as 30 years for the entire roofing system. In some cases, the warranties can even include the removal and replanting of the vegetation if a leak needs to be repaired.
In addition, using a vegetative roof over the membrane can reduce the risk of hail or wind damage to roofs. Airborne debris such as tree limbs and other windblown items is also much less likely to penetrate the roof during a storm.
Damage caused by human error is another common cause of roof leaks. A maintenance technician may have an object such as a rock or a fastener screw on a shoe bottom and cause damage or even punctures to the roof as they walk across it. Even when walkways are provided and clearly marked, workers don't always follow the rules.
3. Why Are Green Roofs Environmentally Responsible?
Today's tip is the reasons why green roofs are an environmentally responsible choice. That's certainly a common-sense notion, but let's take a look at why.
First, a bit of definition: There are two varieties of green roofs: intensive and extensive.
Intensive green roofs are the fancy kind, most often recognized as roof gardens that allow people to walk around and relax. They often include flowers, bushes, and even small trees. Extensive green roofs are usually less involved, with a thinner planting medium, and usually include smaller plants with shallower roots, like grass and flowers. They have a saturated weight of 12 to 50 pounds per square foot.
Green roofs can save a building energy because the added insulation they provide do not allow heat from the sun to penetrate the building. A study by National Research Council of Canada found that green roofs reduced demand for air condition by 75 percent. Green roofs also help reduce the urban heat island effect because they absorb energy that would otherwise be reflected back to the atmosphere, cooking cities more so than their outlying suburbs.
Green roofs also help prevent stormwater from overtaxing storm drains by absorbing rainwater. According to Green Roofs, Healthy Cities — an organization promoting the benefits of green roofs — depending on the type of plants and thickness of the growing medium, green roofs retain 70 to 90 percent of the precipitation that falls on them in the summer and 25 to 40 percent in the winter.
Finally, green roofs improve air quality because plants filter noxious chemicals and can capture and absorb airborne pollutants.
4. Your Garden Variety Roof
Hello. This is Greg Zimmerman, executive editor of Building Operating Management magazine.
Today’s topic is green roofs, specifically what to be aware of if you’re considering a green roof for your next project.
By green roofs, I mean REAL green roofs – the ones with plants, foliage and other greenery, as opposed to cool roofs, which are sometimes labeled green in the sense of being environmentally responsible because they can reduce energy use.
With that distinction made, here’s another one: There are two varieties of green roofs. Intensive green roofs are the fancy kind, most often recognized as roof gardens that allow people to walk around and relax. They often include flowers, bushes, and even small trees. Extensive green roofs are usually less involved, with a thinner planting medium, and usually include smaller plants with shallower roots, like grass and flowers.
Two important considerations when selecting a green roof are waterproofing and weight. Green roofs are much heavier than traditional roofs, so selecting a green roof means making sure the facility has sufficient load-bearing capacity. Because of their much thicker planting medium, intensive green roofs can weigh upwards of 120 pounds per square foot.
The waterproofing system for a green roof can be either a sheet system, a built-up system or a fluid-applied system. Many experts recommend a waterproofing system without seams to reduce possible water-entry points. Waterproofing is certainly the one area where you don’t want to value-engineer.
If a green roof is waterproofed and installed correctly, it can last many years longer than a traditional single-ply roof. Other potential benefits of green roofs include better aesthetics, reduction of the urban heat island effect, energy savings, and reduction in stormwater runoff.
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