Costs for green
roofs in the United States are estimated to average between $15 to $20
per square foot for all use types, i.e., high density residential,
commercial, industrial etc.1
These costs include all aspects of green roof development, from the
waterproofing membrane to soil substrate creation to planting. By
far the highest costs associated with green roof creation are the soil
substrate/growth medium and the plant components associated with it.
Green 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. The cost of planting can also
increase if plants are placed individually rather than pre-grown on
vegetation mats.
Green roof at a
Life Expression Wellness Center in Pennsylvania
(Source:
Roofscapes, Inc.)
The often customized
installation methods in the U.S. stand in sharp contrast to the green
roof creation practices of other countries such as Germany, where an
entire service industry has evolved in response to green rooftop
development and costs run between $8 and $15 per square foot. Because this is
relatively new technology in the United States, much information is
still lacking about the full range of 'traditional' and 'public' costs as well as the long-term benefits
of green roofs. A potential client may still lack a thorough
understanding of the direct, tangible and long-term economic benefits of
building a green roofing system.
Different types of
installation costs include initial capital costs, ongoing maintenance
costs, and lifecycle costs (i.e., green roof replacement might cost more
than conventional roof replacement). Green roof technology often
requires that maintenance costs be built into the original budget,
especially with more elaborate, extensive green roof covers. Long-term
ancillary costs related to the increased costs of insurance, and
liability issues in regards to weight, drainage, interior damages from
roots, damage to walls and liability to personal injury are potential
concerns.2
Offsetting the
initial capital and ongoing maintenance costs, green roofs provide a
number of long-term cost savings. Rooftop vegetation moderates the
temperature extremes of a roof surface and prevents it from being
exposed to ultraviolet (UV) radiation and cold winds that could
accelerate its break down. The result is an extended life span for the
roof. A vegetated roof, on average, can be expected to prolong the
service of the life of a conventional roof by at least 20 years (ZVG,
1996). When the savings associated with deferred maintenance and
reduced energy consumption are taken into account, vegetated rooftops
are comparable in cost to conventional roofs.3
Other long-term
economic advantages to consider in the construction of green roofs,
which can further offset their initial construction costs, include:
Direct and
indirect cost savings opportunities for the building owner, such
as:
·
Increased insulation value, resulting in savings on energy heating
and cooling costs.
·
Potential for greenhouse gas emissions trading credits.
·
Provision of amenity space and aesthetic appeal, increasing the
value of the property and the marketability of the city as a whole.
·
The possible easing of impervious coverage restrictions for
developers who incorporate green roofs into their site plans.
·
Visual and environmental benefits that increase property value.
Cost savings
in terms of environmental benefits to the community include:
·
Cost savings from increased stormwater retention, attenuation of
peak flows and urban flooding, through the reestablishment of
predevelopment hydrology.
·
Decreased need to expand or rebuild separate storm sewer system
infrastructure due to a decrease in total hydraulic loads.
·
The reduction of pollutant loads to receiving waters by nonpoint
source pollutant treatment through nutrient cycling of the plants
and the soil chemistry of the rooftop matrix.
·
Decreased cost of meeting greenhouse gas reductions and the ability
to “bank” heat gains from the "Urban Heat Island Effect."
4
·
Possible acoustic insulation benefits of green roofs in areas of
high noise such as near airports or in the heart of major urban
areas.
·
Quality of life benefits through the additional ecosystem and
environmental amenities achieved through habitat and biodiversity
preservation.
1
Scholz-Barth,
K., 2001: Green Roofs, Stormwater Management From the Top Down.
Environmental Design and Construction. Accessible at http://www.edcmag.com/.
2
Peck,
S.W. and C. Callaghan, 1999: Greenbacks from Green Roofs:
Forging a New Industry in Canada. Prepared for: Canada Mortgage
and Housing Corporation. Environmental Adaptation Research
Group, Environment Canada.
