The Casper Journal :: Casper's Community Newspaper

Imagine looking down from high above on numerous city blocks consisting of mile after mile of building after building and seeing all “green roofs.” Imagine also the huge beneficial effects of the kind of scenery one would be viewing.

As environmentally friendly people continue to look for ways to lessen damaging effects on our environment, plants and gardens will play an ever increasingly larger role.

What are green roofs? A green roof consists of vegetation and soil planted over a waterproofing layer (with minimal degree of structural impact) -- rooftop gardens that reduce urban heat “islands” by providing shade and release of water from plants to the surrounding air.

According to the EPA, green roof technology was first experimented with in Germany more than 30 years ago, supposedly inspired by the rugged sod roofs and walls that prevailed in Iceland for hundreds of years. The popularity of green rooftops has spread over Europe due to their positive environmental attributes, as well as their aesthetic benefits.

Other benefits of a green rooftop are reducing sewage system loads by utilizing large amounts of rainwater (researchers estimate that three to five inches of soil will absorb 75 percent of rain events that are one-half inch or less), absorbing air pollution and protecting underlying roof materials by eliminating exposure to the sun’s UV rays.

Green rooftops also serve as environments that provide habitat for birds and other small animals, reducing noise from the outdoors (five inches of plant medium can lower noise by as much as 40 decibels), and they can insulate a building from extremes in temperatures by keeping the building interior cooler in the summer and warmer in the winter.

Information available reveals there are two kinds of green roofs, one described as intensive and the other described as extensive. The extensive green roof garden requires only one to five inches of soil depth and is capable of including many kinds of vegetative ground cover and grasses.

The type of planting medium used is particularly significant. Organic content, pH and nutrient levels, weight, porosity and water retention capacity all need to be evaluated, just as they would in a regular garden.

But because of its location, the green roof medium must be substantially lighter, less rich and more porous than soil used for a ground-level garden. The result is a self-sustaining garden that will out-compete the weeds.

The intensive green roof has a soil depth that is approximately one foot in depth and will accommodate large trees, shrubs and well maintained gardens, and usually is accessible to the public.

Extensive green roof plants should have most of the characteristics listed below:

* Low growth height

* Rapid growth/spreading

* High drought and heat tolerance

* Fibrous root, as opposed to tap roots, to protect roofing membranes

* No special irrigation or nutritional requirements

* Low maintenance - trimming, weeding, feeding

* Plants shouldn't generate airborne seeds in order to prevent the green roof plants invading other landscaping.

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