Low Impact Development Manual for Michigan - OSEH - University ...

Table 7.16
Vegetated roof types
Extensive
Vegetated Roof
Semi-Intensive Vegetated Roof Intensive Vegetated Roof
Maintenance Low Periodically High
Irrigation (after plants
are established)*
Plant Communities
No Periodically Regularly
Moss, Sedum, Herbs,
and Grasses
System build-up height 60-200 mm 120-250 mm
Weight
60 - 150 kg/m2
13-30 lbs/sqft
Grass, Herbs, and Shrubs Perennials, Shrubs, and Trees
120 - 200 kg/m2
25-40 lbs/sqft
Construction costs Low Medium High
Desired use
Ecological protection
layer
150-400 mm
Underground garages = > 1000 mm
180 - 500 kg/m2
35-100 lbs/sqft
Designed vegetated roof Park-like garden
*Irrigation is required regularly to establish plant communities, especially during the first season.
Source: Adapted from International Green Roof Association
Growing medium: The growing medium is the basis
of the vegetated roof. A sufficient depth for the root
zone has to be ensured as well as an adequate nutrient
supply and a well balanced water-air relation. Depending
on the type of vegetated roof and the construction
requirements, a variety of different system substrates
are available.
Light-weight mineral materials, with high water retention
capacity and good water permeability, such as lava,
pumice, expanded clay, expanded schist, and clay tiles,
have proven to be reliable for many years. Untreated
organic material and top soil have disadvantages in
terms of weight and drainage function; they are only
used as additions to mineral substrates.
Plant level: The plant selection depends on the growing
medium as well as local conditions, available maintenance
and the desired appearance. Low maintenance,
durable and drought resistant plants are used for extensive
vegetated roofs, versus, a nearly limitless plant
selection for intensive vegetated roofs.
Variations
Some specialized vegetated roof companies offer
installation using vegetated blankets/mats or trays. Prevegetated
blankets/mats are grown off-site and brought
to the site for installation (similar to the concept of sod
for grass). They can provide an immediate vegetative
coverage which can prevent erosion, reduce installation
times, and reduce maintenance during what would
otherwise be the establishment period for vegetation.
Frasier School District is testing both the tray system
(foreground) and mat system (background} on their
operations and maintenance building.
LID Manual for Michigan – Chapter 7 Page 304