Environmental Engineering Reference
In-Depth Information
Figure 8-8
Boston World Trade Center, Boston, Massachusetts.
(Courtesy of
Roofmeadow, Inc.)
that bunchgrasses and resinous shrubs may not be approved for projects
that must follow strict fire fuel management guidelines.
c. A variety of species and growth forms should be considered for a vege-
tated roof project, to ensure survival and growth of species that happen
to succeed for the project's particular conditions.
d. Because many perennials and annuals are dormant during part or all of
the rainy season, evergreen and cool-season plants should be included
to help with rainfall interception and evapotranspiration when rains typ-
ically occur.
e. Plant species should not develop a deep taproot.
f. Long life (or self-propagating), with low maintenance and fertilizer
needs.
g. Mature plant size should be factored into the load-bearing capacity of
the roof (e.g., mature perennials can add approximately 2 to 5 lb/ft
2
).
13. Roofs with pitches exceeding 2 : 12 (9.5
◦
) will require supplemental mea-
sures to ensure stability against sliding.
Runoff Water Quality Mitigation
Direct runoff from roofs is a contributor to
non-point source pollutant releases. Vegetated roof covers can significantly reduce
this source of pollution. Assemblies intended to produce water quality benefits
will employ engineered media with almost 100% mineral content. Furthermore,
following the plant establishment period (usually about 18 months), ongoing
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