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Tell me more about Plymouth Library’s green roof.
The new Plymouth Library has a number of roofs. The sloped areas are the green roofs and the flat areas are traditional roofs. There are three separate green roofs:
• Above the teen zone
• Above the main public library space
• Above the staff work areas

What happens to the water on the roof?
The roofs slope at a pitch of 2:12 (2" vertical for every 12" horizontal). At the low points of the green roofs, a series of drains carry away excess moisture and deposit it into the storm water management pond on the east side of the parking lot.

How is the green roof constructed?
The green roofs are composed of multiple layers of materials. Starting from the lowest point, the layers are:
• The metal deck
• A layer of sheathing
• A waterproofing membrane
• Rigid insulation
• Drainage board
• Filter mat
• Growing medium (specially formulated soil for plants)
• The plant materials
• Crushed stone around the perimeter

What kind of plants are on the green roof?
They are Minnesota native perennial plants. A water service pipe on the roof irrigates the plants during dry spells.

How do the flat roofs work?
The flat roofs do not have plants. Instead, they are typical roof systems used on most county buildings. The flat roofs have numerous drains to remove the moisture and drain it into the storm water management pond.

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