Green Roofs

 

A colorful green roof at the Cincinnati Zoo & Botanical Gardens.

The idea of green living is popular right now, and what better place to start than in the garden? Saving energy, reducing impact, and reusing materials are all part of going green. Ironically, one of the most intriguing places to put your new environmental awareness into practice may not be in the garden, but above it.

The idea of a living roof is not new. In Scandinavia, people have been building roofs with sod since the Middle Ages. And you’ve probably heard of the Hanging Gardens of Babylon? Of course, modern life and building practices bring new needs, and planted roofs continue to offer many benefits. Making a roof “green” extends the life of the roof, reduces water runoff and reduces energy costs (especially for cooling) up to 40%.

Plants absorb sunlight, whose energy would otherwise go into heating a roof’s surface. The evapo-transpiration of plant leaves also helps absorb and dissipate heat. Succulents are often used because roof environments are similar to high desert plateaus: intense rain events that drain quickly, alternating with dry reflective heat.

There are two types of “green roof” building systems, each defined by the depth of the planting medium (soil is not used, due to its weight). “Extensive” systems are less than 6” deep, and use mainly succulents. These systems are lighter, less expensive, and easier to maintain (though “lighter” can still mean up to 25-30 lbs/sf). “Intensive” systems are more than 6” deep and can support larger and more water hungry plants such as grasses, meadow flowers and even vegetables. These systems are heavier, and may require reinforcing a roof to support their weight (they are more common on reinforced concrete roof decks). Some commercial or public roofs may be designed to hold shrubs or trees.

A residential green roof. This one is a modular extensive system, planted primarily with various Sedum species. The paver patio will be a nice place to have morning coffee (but not too close to the edge!).

Most residential green roof systems are modular extensive systems, meaning they are made up of identical individual units, and may be fit together to cover a large range of custom shapes. These are laid on top of a thick waterproof membrane. The system might also include structures for drainage or drip irrigation. Modular systems also have the benefit of being pre-planted, meaning plants are full grown and offer immediate effectiveness at installation (it also means you have to weed them less).

If you have a sloped roof, fixtures such as baffles and parapets are used to lock units in place. Slopes of up to 15 degrees are easily accommodated, though slopes of up to 35 degrees are possible. Sloped surfaces require more irrigation, or a more closely tailored plant selection, since the higher end of each unit will be drier than the lower end.

It is now easier than ever to surround yourself with planting space, letting you indulge your gardening obsession and greening your environment to boot!

 

Posted by Jennifer Schneller on July 29, 2012

https://hortitude.wordpress.com/2012/07/29/green-roofs/