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4  FM quick reads on Green roof

1. What To Think About When You

Green roofs are certainly not a new idea. The Hanging Gardens of Babylon — one of the Seven Wonders of the World — was essentially a green roof, and they were built about 600 BC. But it's only been the last dozen years or so, as green building has grown up, that green roofs have returned to prominence. In 2001, when the first municipal green roof project in the U.S. was completed on Chicago's City Hall, green roof advocates had a high-profile case study to point to verifying the applicability of green roofs on commercial facilities.

Green roofs have several benefits: They reduce the urban heat island effect and stormwater runoff; they can keep buildings cooler in the summertime, reducing air conditioning costs; they act as a layer of insulation, potentially reducing heat costs in the winter; and they can provide urban facility occupants a soothing environment for breaks.

But there are several things to think about if you are considering a green roof. First and foremost is cost. Green roofs are expensive compared with traditional roofs, and it's hard to make the case for a green roof strictly on a return on investment basis. Also, they are heavy, so if you're considering a green roof as a retrofit, the facility may require extra structural support. Waterproofing is sometimes an issue, as well.

But, again, as green roofs have become more and more popular, there are more and more experts that can help guide you through the process. And more and more manufacturers are offering high-quality green roof products.

2.  How Do Commission Your Roof?

Today's tip, from David Reid and John Wilkins of Gould Evans Architects, is about strategies you should consider when it comes to commissioning your roof.

Most facility managers understand "commissioning" as a strategy that only applies to HVAC systems. But commissioning roof installations is a critical component of a water-tight and energy efficient roof.

Reid and Wilkins suggest three areas to examine when commissioning roofing.

First, look for "weak links" in the integrity of the roofing system, as most of the failures result here. Look at roof terminations, penetrations, flashings at corners, intersections, eaves, curbs and parapets, and drainage systems.

Secondly, especially if you're installing a green roof, but really for any roof, double and triple check that the waterproofing membrane truly is water tight. Perform a leak-detection test appropriate to the type of membrane you've installed. For example, flowing tests flow water continuously over the surface of the waterproofing membrane for a minimum of 24 hours without closing the drains or erecting dams. Electric field vector mapping pinpoints breaches in the roof membrane by tracing the flow of an electric current across the membrane surface.

Thirdly, part of commissioning the roof is creating a plan to protect the membrane until construction is completed and all components - including HVAC, etc. Reid and Wilkins suggest a product called protection board to make sure the roof isn't penetrated or damaged during the rest of the installation or construction process.

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.  What to Consider When Picking Green Roof Plantings

Today’s tip is about considerations when selecting the plantings for a green roof. The two types of green roofs – extensive and intensive – have different requirements when it comes to the structure of the facility, planting medium, and below-plant layers. But the same piece of advice regarding types of plantings applies to both: Use plants that are as self-sustaining as possible. That means that it’s almost always best to use plants that don’t need as little supplemental irrigation as is necessary to keep the plants alive. In other words, use plants that can survive on their own with natural rainfall.

Green roofs are almost always either part of new construction, or part of larger renovation projects. This means there are often lots to think about, and sometimes a green roof product or design is selected without any thought given to its maintenance requirements or the cost of supplemental irrigation water. An important facet of this is that if plants aren’t watered regularly and dry out, they can become more of a fire hazard. It’s important to have these risk management conversations early on in the design process.

Some experts suggest that the most maintenance a green roof should need is going up once a year to do a routine weeding. Put as much time into planning the landscape of your garden roof as you would in planning the landscape around your building. The operations and maintenance cost implications may be similar!


Green roof , urban heat island effect , stormwater runoff

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