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Physical Issues
 Waterproofing Integrity-
Water leakage from drainage backups or possible root puncture could lead
to interior damage if the correct waterproofing membrane system, root barrier
and drainage layer are not selected. Vulnerable areas where leakage is possible
include abutting vertical walls, roof vent pipers, outlets, air conditioning
units, perimeter areas, etc.
Pesticide Leakage from roof Materials- The potential does exist for certain
elements, such as iron and aluminum, to seep out and infiltrate ground water.
Care must be exercised in selecting thick membranes to ensure no release
of pollutants, and the materials used in foundations and pathways on a green
roof should not leach carbonates.
Additional Support Considerations- For extensive and intensive green roofs
with projected live loads higher than 17 pounds per square foot, consultation
with a structural engineer is required. Considerable costs can be associated
with these high interactive projects, especially with renovation or retrofitting
projects.
Unwelcome Wildlife Problems- A natural habitat could perhaps invite some
undesirable creatures. Because of the watertight integrity of the system
it would be extremely difficult or impossible for the animals to enter through
the roof.
Environmental Issues
Native vs. Cultivated Plants- Is it environmentally correct to use plants
other than natives on green roofs? Purist would probably say that only native
plants should be used in most landscaping projects, including green roofs.
The green roof plant palette is somewhat limited, however due to their exposure
to harsher climatic conditions. Also, current green roof technology is imported
from Europe with proven plant species and many of these are readily cultivated
and available here. Green roofs will only function if the vegetation is
successful, so initially it may be necessary to use proven adaptive species,
and then introduce and promote our own native plants, as they are proven
successful.
Irrigation Requirements- A hot and dry climate would dictate a distinct
list of plants that are extremely drought and heat tolerant, especially
succulents. Many species that grow in full sun have developed mechanisms
to reduce leaf evaporation. Any landscape requiring regular irrigation would
be high maintenance and expensive in terms of supplemental water usage and
cost. Techniques have been developed to automatically capture and release
stored rainwater within the green roof system. Although these details would
increase the initial capital investment cost of the green roof, they would
quickly pay for themselves in terms of irrigation savings, as well as providing
an argument for sustainability.
Aesthetic Values
Some people may feel organic architecture is inappropriate or "unnatural"
for any building. If no maintenance is desired, then the design must dictate
the correct choice and placement of plant material. A handsoff program may
result in a wild and overgrown look. Beauty is in the eye of the beholder,
but surely the many arguments for the ecological and economic benefits of
green roofs can outweigh aesthetically weak designs.
One issue holding back the eco-roof movement in this country is the lack
of solid research on materials and techniques published in English. Very
little testing has been done on green roofs in this country. As a result,
individual designers must continually reinvent the wheel in implementing
their designs.
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