Conservation Gardening in Practice: Installing a Green Roof

Benefits of green roofs

Green roofs, also called ecoroofs, vegetated roofs, and living roofs, offer a more sustainable alternative than traditional roofs because they provide several important environmental and economic benefits:

1. They last up to twice as long as traditional roofs
2. They slow the progression of rain into the stormwater system
3. They mitigate urban heat island effects
4. They provide an insulating layer to buildings, keeping them warmer in winter and cooler in summer, which decreases costs related to heating and cooling
5. The vegetation absorbs carbon dioxide and produces oxygen
6. They create habitats for wildlife

For more benefits see:

The benefits of, and incentives for, green roofs , Green roofs provide many benefits,  Water quality benefits,  and Why Green Roofs

Green roofs in practice

Green roofs are very popular in Europe because their environmental benefits have been recognized there since the 70s. But it has only been in the last ten years or so that green roofs have begun to be utilized in the U. S. Several American cities, such as Portland, Chicago, and Washington D. C., have instituted incentive programs for developers who include green roofs in their new construction projects. The Home Depot Foundation, in February of 2007, gave a $300,000 grant to the non-profit organization, Green Roofs for Healthy Cities to foster green infrastructure in several other cities.

I, personally, would like to see Home Depot put its mouth where its money is. According to their corporate website, there are 2,274 Home Depot stores in the U. S. Each store has a roof approximately the size of a football field. Add to this the size of the enormous parking lot surrounding each of these stores, and that is a vast amount of impervious surface area. It is not just Home Depot either. There is a shopping center near my home which has a Lowes, Best Buy, Petsmart, Raymour & Flannigan, Target, Office Max, Bed, Bath & Beyond, Dicks Sporting Goods, Old Navy, Barnes & Noble, DSW Shoes, and a Giant grocery store. This site is over 100 acres, and all the space between the stores is a parking lot.

Imagine the decrease in stormwater runoff into our watersheds if every one of these stores all across the country installed a green roof! Or imagine if all of these facilities installed solar panels above their green roofs? We could make a significant contribution to renewable energy just from using all this space on top of these megastore roofs. Fortunately, I have found that I am not alone in this feeling. In a study funded by the EPA and the Target corporation, low impact design standards for big box stores have been proposed. Alas, we cannot wait for this to happen, but instead must become responsible for our own small slice of land.

Installing a green roof

A green roof consists of several layers:

1)      an insulation layer

2)      a waterproof membrane

3)      a drainage layer

4)      a filter layer

5)      a layer of growing medium. When installing a green roof, it is important to determine that the roof in question is structurally able to hold the additional weight of materials on top. Consult a structural engineer if you are in doubt.

There is a wealth of installation instructions and examples at the skygardens blog and at greenroofs.com

Green roofs and wildlife

• green roofs providing habitat for endangered Bay Checkerspot Butterfly in California
• green roofs for San Francisco Mission Blue Butterfly and San Bruno Elfin
• Green roofs provide habatat for endangered butterflies
• A great visual resource is Nigel Dunnett and Noel Kingsbury’s Planting Green Roofs and Living Walls

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© 2009 – 2010, Carole Brown. All rights reserved.

Tagged as: Butterflies, green roof, habitat loss, Water Conservation, wildlife habitat gardens