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Photo Credit - Building Logics View Extensive Greenroof ComponentsExtensive Greenroofs
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These low profile vegetated roof systems are the lightest of the three systems usually between 12-25 lbs./sq.ft. They typically are also the least expensive around $16-$22/sq.ft. These systems are optimal for steeper pitched roofs or where it is hard to access the roof, but they are also used all the time for flat applications.

Extensive greenroofs require minimal amounts of maintenance especially after the plants reach maturity. These systems are suitable for renovation projects and large expansive areas that are going to be vegetated because the plants grow quickly and fill in empty areas forming a dense "green mat". The "greenroof plants" are relatively drought tolerant and typically don't require an irrigation system. These plants also get a majority of their nutrients from rainwater and the air so, these systems usually don't require fertilizer. Designers can incorporate water retention systems into the design that will hold stormwater and nutrients for longer periods of time that also help a plants vitality. Attached is a preferred plant palette that I use for projects in the Mid-Atlantic region.

These systems function the best when you have about 4" of soil because that allows about 1" of rainwater to collect after a rain event. The soil mix used for the growing medium is about 70% expanded shale, 20% sand, and 10% organic compost. There usually isn't any problems with invasive species or weeds in these systems as long as the organic material doesn't become too excessive. Modular trays or pre-grown vegetated mats can work well in these applications.

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