Facilities managers can take advantage of wasted roof space and reap the benefits of going green with vegetative roofs. As opposed to a blacktop roof that absorbs a lot of heat, a vegetative roof provides better insulation, saves on cooling costs and encourages cooler urban air temperatures through evapotranspiration (the natural release of water from plants). This roof alternative is also great for absorbing sound in noisy areas, such as airports, and retaining rainwater, putting less stress on gutters and sewer systems.
Although vegetative roofs offer many benefits, some facilities managers shy away from them because they require a bit more attention than traditional roofs. But planning well and choosing the right structure and plant material can keep the maintenance to a manageable level, says Peter D'Antonio, national sales manager for waterproofing systems at Sika Sarnafil, a roofing and waterproofing system company based in Canton, Mass., and one of the largest providers of green roof systems worldwide.
To select the best vegetation for easy maintenance, consider this expert advice:
- Try using many varieties of sedum plants, such as “hens and chicks” type plants, because they are very hardy and extraordinarily resistant to harsh conditions and temperature extremes, says Tad Floridis, COO and director of business development for Greensulate, a green roofing systems company based in New York City. Though not as pretty as roses, these plants are well suited for the harsh exposures that green roofs endure, he says. Typically seen in alpine and desert settings, sedum plants come in a wide variety, can be shade tolerant and often don’t require much irrigation, Floridis says. In addition, many sedums reach only two to four inches in length, so they don’t need to be pruned.
- Avoid plants that spread aggressively. “Invasive plant species, such as bamboo and vines, should be avoided at all costs because they can destroy the vegetative part of the green roof by becoming too dominant and possibly compromising the waterproofing,” D’Antonio says. “I’ve seen bamboo literally displace planters constructed of brick.”
- Determine whether native plants can survive. Although native plants are typically preferred for conventional landscaping at ground level, D’Antonio says there is some debate in the industry about how effective they are for roof vegetation. A roof environment receives more sunlight and wind, which may not be tolerated by some native plants.
- Consider a prefabricated option. Modular tray systems come with pre-grown plants on corrugated rubber trays, and they can be placed directly on the roof membrane. “They can create an instant fully established and monolithic green roof look,” Floridis says. Although these systems are often more expensive up front, you’ll start enjoying the visual benefits of a green roof immediately, and you won’t have to deal with the frustrations of building a vegetative roof from scratch.
Floridis says his company’s maintenance plans usually require twice-weekly visits from April 1 to November 1 and twice-monthly visits from November 1 to April 1 (most plants are dormant during this time). Maintenance includes:
- Weed and other interloper removal, especially at first when the plants will be going through a survival-of-the-fittest phase.
- Trimming trees and shrubs and removing dead plant material.
- Making sure drains are clear of any debris.
- Irrigating and fertilizing all vegetation, and testing soil samples for nutrient levels.
- Doing a semi-annual audit of the vegetative roof to gather plant performance and other data for the company’s green roof system database. D’Antonio also recommends doing an audit of the roof during any extreme climate changes, such as a drought.
If you decide to install a green roof, have a thorough discussion with a vegetative roof specialist to ensure you’re prepared for the maintenance required and that your plan addresses any important fire and safety codes. Exploring your options and your building’s environment will help you design a green roof that meets your specific needs. And you’ll become part of a growing trend.
“There’s really a movement across the country,” D’Antonio says. “People are realizing a green roof is more than just an ornamental addition to a building and is becoming an important method in mitigating the urban heat island and helping to reduce stormwater discharge.”
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