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

Technical requirements
Root resistant waterproofing is necessary for pitched
vegetated roofs; installing an additional root barrier,
requires much effort and increases the risk of slippage.
Stable abutments have to be installed on the eaves
edges to transfer shear forces from the vegetated roof
system build-up and the additional snow load into the
roof construction. Additional shear barriers may be
necessary to transfer the shear forces depending on the
roof slope and the roof length. It is recommended the
design for the shear barriers and the eaves profiles be
done by a structural engineer. With increasing slope,
the vegetated roof system build-up is more complicated
and the substrate has to be protected from erosion;
plastic grid elements can be used for this purpose.
Example parapet flashing detail for a flat roof
Source: Roofscapes, Inc.
Pitched Vegetated Roofs
Plant selection
The success of the landscaping on pitched roofs
depends on the plants. Fast surface coverage is the
highest priority. A dense planting of root ball plants
or pre-cultivated vegetation mats are used in cases of
steep slopes and allow for rapid coverage. It is also
important to consider the exposure of the roof area, the
slope and the location of the building when selecting
plants. Perennials and grasses can be used whereas
Sedum is the most suitable for pitched roofs, due to
the species’ high water retention capacity and erosion
protection. The water run-off is much faster on pitched
roofs compared to a flat roof. It is advisable to plan for
an additional irrigation system to provide water during
dry periods. The irrigation can be provided either by
drip irrigation or by sprinkler systems.
LID Manual for Michigan – Chapter 7 Page 310