What to consider when building a green roof

One strategy for addressing impacts associated with urban development is to reduce the functional area of developed surface.  The European community, and especially Germany, has opted to do so by re-vegetating roofs.  Green roofs have been associated with a variety of environmental and economic benefits, including the ability to retain precipitation, filter pollutants, reduce maximum rooftop temperatures, insulate buildings, and reduce the urban heat island effect.  Interest in green roof development in the United States has recently spiked, and the industry continues to grow consistently.

Investigations into the effectiveness of green roofs, however, have shown that not all green roofs perform equally.  In order to ensure that a green roof functions as desired, it is important that the designer considers several factors.  These include:

– desired endpoint (e.g., is roof being constructed to provide habitat, buffer stormwater, beautify, etc.?);

– type of roof (e.g., whether an intensive roof — park-like, interactive, relatively high maintenance, and typically heavier — or extensive roof — non-interactive, low maintenance, lighter — is appropriate for the functions desired);

– whether structural modifications are necessary to handle additional weight associated with the green roof;

– overall composition of roof system (e.g., whether to include water retention mats, depth of substrate);

– proper substrate formula;

– which mix of vegetative species will grow well together and perform expected functions, and;

– time to maturity and establishment method for vegetation (obtaining sod-like pre-grown vegetation mats, planting on-site as plugs, or planting on-site as shoots).

In my next several posts, I will explore these questions and others as I identify methods for installing a green roof system for the Eco Brooklyn show house.  I will review primary literature, information available from practitioners, and identify supply chains in the New York City area.  The project will culminate with the installation of the roof.

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