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Photo Credit - Earth Pledge View Semi-Intensive Greenroof ComponentsSemi-Intensive Greenroofs
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These vegetated roof systems often involve a combination and a mixture of characteristics associated with both extensive greenroofs and intensive greenroofs. These systems usually are between 4"-12" in soil depth and typically weigh between 25-60 lbs. These systems are ideal for flat roofs that are partially accessible. Often these roof systems will include an amenity such as a roof plaza and may contain a mixture of hardscape and landscape materials. The cost for these systems typically will run between $25-$50/sq.ft. based on the amount of plant material proposed, the types of hardscape material proposed, and if elements such as lighting, irrigation, and site furnishings are included in the design.

Usually, these systems are installed on either metal or concrete deck systems which can support the extra weight and the waterproofing can either consist of high performing membrane or liquid applied product. Often additional water retention mats may need to be specified if there are a lot of plant materials specified such as perennials or shrubs especially, if an irrigation system is not proposed. Semi-intensive roofs typically require a little more annual maintenance but also allow for a greater amount of plant diversity and wildlife habitat if desired.

The lightweight soil mix for these systems are composed of 55% expanded shale, 25% sand and 20% organic material and will tend to hold between 1-3" of rainfall. It is important to make sure that a good drainage board or mat is specified so that the plants can get an adequate amount of aeration to their root systems to avoid constant saturation.

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