Quick Definition

A green roof or living roof is a roof of a building that is partially or completely covered with vegetation, planted over a waterproofing membrane. (Wikipedia)

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In Depth

Green roofs have many benefits: The vegetation insulates the roof from heat gain, and extends the life of the roof membrane from UV degradation that occurs on many flat roofs. Green roofs also retain rainwater, which helps mitigate stormwater runoff and cools the roof during the evaporation process. Green roofs also create a habitat for birds and other wildlife.

The two types of green roofs are intensive and extensive. Intensive green roofs typically have a soil section of six inches or more and can sustain a variety of plant types with deeper roots. Intensive green roofs are substantially heavier, require more structure to support and may need irrigation systems. Plants for this type of roof have to be carefully selected based on climate and region.

Extensive green roofs have shallow soil section of two to four inches. Plants typically used on extensive green roofs are succulents, sedums and some perennials. This type of green roof is lighter and does not require extensive structural changes to the design of the home. Irrigation is not needed when using rugged plants like sedums and succulents.

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Our Application

In New Orleans, our Shigeru Ban house has an extensive green roof with sedums. The roof under the plants is TPO and the plants were pre-grown in interlocking containers that sit directly on top of the TPO. The installation was fast and easy.

Our Newark apartment building has a partial green roof and community garden.

In our Kansas City project, currently under construction, our design includes a green roof over a parking lot.

Lessons Learned

Green roofs are a great option, but can also be costly. We have not used them widely on our homes in New Orleans due to the cost of materials and installation.