Greener by Design: Exploring options with ecological roofing


Beyond the obvious aesthetic appeal of rooftop greenery, vegetated roofs offer benefits to the building owner and the larger community.

Energy savings
By modulating rooftop temperatures through evapotranspiration, the evaporative cooling caused by the movement of water through plants, green roofs keep the roof and the surrounding air cool. In winter, the growing media and plant matter act as insulators, protecting against heat loss.

Longer waterproofing service life
Moderating rooftop temperatures also protects the roof waterproofing from extremes of heat and cold, and the plant covering prevents direct sunlight from degrading the roof membrane. Although the growing media and vegetation can make leaks more difficult to locate and repair, if the waterproofing system is designed and installed properly, the plantings offer protection from the wear and tear of direct exposure to the elements.

Stormwater retention
As part of many cities’ efforts to combat sewer system overload, building codes are increasingly calling for provisions for stormwater management. In New York City, for example, the NYC Green Infrastructure Plan requires greater onsite storage of stormwater runoff and slower release to the sewer system to reduce peak discharges during rain events. Here, too, vegetated roofs have an advantage over conventional systems—plants and soil naturally retain and filter rainwater, releasing runoff slowly over time.

Habitat and environment
In large cities where vegetated areas are few and far between, roofs offer an opportunity to create a natural oasis in even a dense urban setting. Some extensive green roofs have been designed to replicate local ecosystems and serve as a waystation for migrating birds and butterflies. A view of greenery or access to an outdoor garden has been shown to improve patient outcomes in hospitals, increase productivity in offices, improve academic success in educational settings, and have a general positive impact on health and well-being.

Structural concerns
Before opting to add a vegetated roof to an existing building, one should consult an engineer to conduct a structural evaluation of the existing roof. The analysis should consider the saturated weight of the components, along with the load from increased foot traffic and additional maintenance equipment. Adding a vegetated assembly could also impact wind, snow, and rain design loads, so these modifications must be taken into consideration as part of the structural calculations.

Waterproofing design
Selecting the right waterproofing system is especially critical with vegetated roofs. Once the roofing membrane is buried below plantings, soil, drainage media, pavers, root barrier, irrigation systems, and other elements, it is difficult and expensive to locate and repair a leak. A resilient, multi-layered system that is durable and compatible with overlying plant matter is critical to the long-term durability of any vegetated roof. To confirm membrane watertightness, flood testing or other methods of leak detection are recommended before installing green roof components.

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2 comments on “Greener by Design: Exploring options with ecological roofing”

  1. What a nice overview of these issues. Vegetative/green roofs are a great amenity for inhabitants and building owners and EPDM membrane is commonly used as the roof cover. A small correction … prior to the 2010 edition of ASHRAE 90.1, there was no requirement for roof reflectivity. That provision was added for the 2010 edition in Climate Zones 1-3. Your statement of “…in previous editions, reflective roof assemblies were the standard, irrespective of geographic region” is incorrect.

  2. Green roofs have become incredibly popular and are being designed and installed at an incredibly rapid pace. As an addition to the “Waterproof design” in this article, I would strongly recommend installing a conductive mesh beneath the waterproof membrane. This will now, always allow for an Electronic Leak Detection to be performed after completion of such elaborate vegetated roofs and/or any other amenity space idea. My company specializes in both high and low voltage testing (leak/integrity), Gaussen’s “Real Time Leak Detection and Alert Systems” (24/7 live monitoring) as well as installing the conductive mesh.
    The recommendation to perform a leak detection prior to installing the green roof components is spot on and will only save time, money and frustration. You can find our specification for Electronic Leak Detection at
    Great article!!

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