Testing vegetative roof systems

Results show potential problems with wind

Vegetative roof systems, sometimes referred to as "green roofs," are rapidly gaining popularity and acceptance in the U.S. For many, the appeal of vegetative roof systems involves their aesthetics and environmental attributes, including reduced storm water runoff, air-quality improvement, mitigation of heat island effects and noise reduction for building occupants.

However, vegetative roof systems' compliance with U.S. building codes is questionable. Although vegetative roof systems' waterproofing components can be tested and evaluated for code compliance bythe same means used for conventional roof systems, vegetative roof systems' growth media and plants largely have been untested for the purposes of code compliance.

Because growth media and plants serve as the topmost surface of most vegetative roof systems, these components are an important consideration in determining vegetative roof systems' wind resistances.

For example, the 2006, 2009 and upcoming 2012 editions of the International Building Code (IBC) restrict the use of aggregate surfacing on roof systems based on maximum building height, basic wind speed and exposure category for the building being evaluated. This restriction is based on the concern that aggregate could scour and become wind-borne debris during high-wind events. For additional information regarding IBC's restrictions on the use of rooftop aggregate, see "What will happen to aggregate?" August 2004 issue, page 61.