Types of Green Roofs

Intensive vs. Extensive and Modular vs. Integrated

Extensive and Intensive Green Roofs

Many types of green roofs can be installed in Minnesota. Some green roofs have less than two inches of growing medium and some have more than a foot of growing medium. Some will only support a few varieties of sedums while others will support native flowers and grasses, highly maintained turf grass, or even trees and shrubs. Generally, green roofs are considered either intensive or extensive roofs.

Extensive green roofs are generally designed to be lightweight and to maximize the performance and environmental benefits that a green roof can bring to a building. Extensive green roofs feature a layer if growing medium that is six inches deep or less and are generally planted with sedums or native plant species. Extensive green roofs are generally not accessible to the public. The issues driving green roofs in Minnesota mean that extensive green roofs are most commonly installed. Extensive green roofs in Minnesota include the Ramsey-Washington Metro Watershed District in Little Canada and the Visitor’s Center at Lebanon Hills Regional Park in Eagan.

Intensive green roofs are generally designed as amenity space that can be used by building tenants or by the general public. Intensive green roofs are generally heavier, include a deeper layer of growing medium, support a wider variety of plants, and have greater needs for irrigation and maintenance. The most visible intensive green roof in Minnesota is probably the lawn bowling club at Brit’s Pub in Downtown Minneapolis. The Crowne Plaza Northstar Hotel, also in Downtown Minneapolis, has an intensive green roof that was originally installed in 1978 and features maple trees that are now ten inches in diameter.

Semi-intensive green roofs include features of both intensive and extensive green roofs. These are referred to as semi-intensive green roofs. The Green Institute’s green roof at the Phillips Eco-Enterprise Center is a highly visible semi-intensive green roof. While the roof features a range of extensive plantings and is designed to be low-maintenance, it is also fully ADA accessible and can hold 30 people for events.

Modular and Integrated Green Roofs

Integrated: Most green roofs installed in Minnesota are integrated green roofs. The green roof components are installed as a series of layers. The Minneapolis Central Library, EastVillage Apartments, and many other local green roofs use integrated systems.

Modular: Modular green roofs are partially assembled off-site and installed in units. Some modular systems feature plastic or metal trays that are filled with growing medium and placed on the rooftop. Plants can be grown in these trays before or after installation. Other systems feature plants pre-grown in mats that are laid onto the roof surface. The Macalester College “fishbowl” green roof in Saint Paul features modular Green Roof Blocks and Green Roof Paks systems. Firehouse 14 in Northeast Minneapolis uses a GreenGrid modular green roof system. The Marcy-Holmes Neighborhood’s Rainwater Resources Recycling project features a Xeroflor green roof on a pitched residential garage in Southeast Minneapolis.