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

Maintenance
• Irrigation will be required as necessary during the
plant establishment period and in times of drought.
• During the plant establishment period, three to four
visits to conduct basic weeding, fertilization, and
infill planting is recommended.
• The soluble nitrogen content (nitrate plus
ammonium ion) of the soil should be adjusted to
between one and five parts per million, based on
soil test.
• Once plants are established, it is crucial to maintain
the roof once or twice a year. Weeds and other
unwanted plants on the entire roof, at the perimeters
and at the upstands need to be removed. For grass and
herb vegetation the organic buildup has to be removed
once a year. Intensive vegetated roofs require higher
maintenance and service throughout the year.
Winter Considerations
Applicable snow load must be considered in the design
of the roof structure.
Cost
The construction cost of vegetated roof covers varies
greatly, depending on factors such as:
• Height of the building
• Accessibility to the structure by large equipment
such as cranes and trailers
• Depth and complexity of the assembly
• Remoteness of the project from sources of material
supply
• Size of the project
Active growth on Fraser public school maintenance green
roof during winter in Fraser, MI
However, under 2007 market conditions, extensive
vegetated covers for roof will typically range between
$8 and $16 per square foot, including design, installation,
and warranty service (not including waterproofing).
Basic maintenance for extensive vegetated covers typically
requires about 2-3 person-hours per 1,000 square
feet, annually.
Although vegetated roofs are relatively expensive
compared to other BMPs in terms of stormwater
management, they can have other significant benefits
which serve to reduce their life-cycle costs. For example,
the longevity of the roof system may be greatly
increased. In addition, heating and cooling costs can be
significantly reduced.
LID Manual for Michigan – Chapter 7 Page 313