25 October 2004
Cost Data. Costs for vegetated roofs in the United States are estimated to
average between 1 and 5 per square meter ( and per square foot) for all
use types (i.e., high density residential, commercial, or industrial).33 These costs
include all aspects of vegetated roof installation, from the waterproofing membrane to
soil substrate creation to planting. By far the highest costs associated with vegetated
roof creation are the soil substrate and growth medium and the associated plant
components. Vegetated roof retrofit projects may have increased cost associated with
traffic and resource scheduling concerns as well as the on-site availability of equipment
and materials. Planting costs are higher if plants are placed individually rather than pre-
grown on vegetation mats.
Maintenance Issues. Once a properly installed vegetated roof is well
established, its maintenance requirements are usually minimal. There are two basic
types of vegetated roofing systems: extensive and intensive.
Extensive roofs form a thin vegetated sheath of self-sufficient mosses,
sedums, and small shrubs. Their low profile allows them to be added to existing
buildings, including those with sloping roofs.
By contrast, intensive roofs are integral to the roof structure, permitting the
use of trees and walkways. A greater depth of media may be required to accommodate
larger vegetation and surface features. Intensive roofs require more structural as well
as horticultural maintenance, similar to a conventional garden, because plantings tend
to be both heavier and more elaborate than on extensive roofs. For both types of roofs,
maintenance requirements typically include inspection of the roof membrane, the most
crucial element of a vegetated roof, as well as inspection and preventive maintenance
Corrective Actions. Corrective actions for vegetated roofs are generally to
repair localized problems. More complex systems may have monitoring devices
incorporated into the membrane. Leak detection systems can be brought to the site to
locate breaches in the membrane. The soil media can be removed and the membrane
repaired. Long periods of drought or loss of soil to high winds may require replacement
of the media or replanting. If drought becomes an issue, corrective actions include
installing an irrigation system or scheduling supplemental watering.
PERMEABLE PAVERS. Permeable pavers allow water to seep through
regularly interspersed void areas in order to reduce runoff and associated pollutants.