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

Modular systems are manufactured trays filled with
various vegetated roof layers (often pre-vegetated as
well) that are delivered to the site and installed on a
prepared roof. Manufacturers of these systems claim
that benefits include faster installation and easier access
to the roof if maintenance or leak repairs are necessary
(in addition to the potential benefits of a pre-vegetated
system). Others argue that these benefits are not significant
and that trays can have drawbacks such as increased
cost, poor aesthetics (module edges being visible), and
reduced performance (wet and dry spots resulting from
the barriers between modules in the system).
Extensive vegetated roofs
Extensive vegetated roofs are the most commonly used
systems due to their higher mitigation of stormwater
runoff as well as their lower cost compared to the other
systems. Extensive systems have three variations of
assemblies that can be considered in design.
Single media assemblies
Single media assemblies (Figure 7.57) are commonly
used for pitched roof applications and for thin and
lightweight installations. These systems typically incorporate
very drought tolerant plants and utilize coarse
engineered media with high permeability. A typical
profile would include the following layers:
1. Waterproofing membrane
2. Protection layer
3. Root barrier (optional, depending on the rootfastness
of the waterproofing)
Figure 7.57
Single media assembly
Installation of green roof at the Ford Rouge Plant in
Dearborn, MI
Source: Rouge River National Wet Weather Demonstration
Project
4. Drainage layer
5. Filter layer
6. Growth media
7. Vegetation
Pitched roof applications may require the addition of
slope bars, rigid slope stabilization panels, cribbing,
reinforcing mesh, or similar method of preventing sliding
instability.
Flat roof applications with mats as foundations typically
require a network of perforated internal drainage
conduit to enhance drainage of percolated rainfall to the
deck drains or scuppers.
Vegetation
growth Media
Filter layer
drainage layer
protection layer
waterprooF MeMbrane
rooF structure
LID Manual for Michigan – Chapter 7 Page 305