Some entities understand the financial benefits and would like to be more sustainable, but are under some pressure to have a “showcase” project that is more interesting and picturesque than energy efficiency or upgrading sophisticated equipment. If you are in that situation, consider rooftop gardens as an effective way to be more sustainable, gain benefits, and have a great “photo op.” Particularly in urban areas, rooftop gardens bring some greenery and an area for relaxation into a “concrete” space.
Rooftop gardens are essentially backyards atop one’s building, bringing “nature” into an otherwise sterile space. Rooftop gardens can be either vertical or horizontal and is an effective way to reduce the heat load on your AC system, saving on energy bills.
Rooftops are, by nature, urban heat islands, absorbing the sun’s radiation and giving off energy slowly, resulting in massive pockets of hot air. In an urban environment of many dark-colored roof tiles and concrete streets, cities are particularly prone to higher than normal summer temperatures because of heat islands, which contributes to worse air quality and mental and physical health concerns. In addition, energy being kept in and close to buildings raises the demand for air conditioning and other cooling equipment, making it work harder and for longer causing a significant rise in energy usage and putting a strain on the local energy grid, which some utilities have trouble maintaining. In addition, the building owner pays for the urban island effect big time as more utilities put a premium charge on high peak demand during the cooling season (summer). Even if a building has one 15-minute period in a month of very high cooling demand, it will be charged a very high amount for this single short-term spike in demand. In addition, heat islands damage roofing material, requiring the building owner to upgrade it more often than if a rooftop garden is installed and maintained to protect the building’s materials.
Rooftop gardens can mitigate this effect because the plants absorb the sun’s radiation, not the roof shingles or underneath part and the shade offered by plants reduces heat transport, resulting in cooler temperatures and improved air quality.
A recent study found that an exposed roof can get as hot as 158⁰F on a sunny day while an identical roof with a rooftop garden covering most of the roof stayed relatively stable at a temperature of 77⁰F (https://www.thespruce.com/green-benefits-of-a-roof-garden-1708536). In addition to providing natural cooling, rooftop gardens can provide a natural sound barrier, delay stormwater runoff, and provide filtered rainwater.
It is critical that the building owner bring in an experienced qualified roof garden designer and installer, who can check about any local permits and regulations that must be adhered to in your jurisdiction. Be sure that the designer assesses your building to determine whether it can hold a rooftop garden, that it can be waterproofed, or whether normal temperature extremes in your area may damage a roof garden or roof. It is crucial to choose the right types of plants depending on your local climate, such as winds and temperature extremes. If this is an office building with periods of inactivity, it may make sense to include low-maintenance plants, needing little water or pruning.
The cost of a rooftop garden will depend on many factors, such as size, plants selected, and construction materials used. A rule of thumb range of initial cost is $15-$40 per square foot of space. However, you should quickly begin to save money on energy bills and a payback in a reasonable time is likely, plus it should advance the building’s asset value and attractiveness for other potential tenants.
CCES does not perform rooftop garden design or landscaping. But we can manage professionals in these fields to do the proper work to install one to maximize your benefits. In addition, we can perform a sustainability assessment of your buildings, company, or assets to determine which strategies are most effective to become more sustainable and to optimize the financial benefits. Contact us today at 914-584-6720 or karell@CCESworld.com.