In a drought-prone area such as Denver, you might think that green roofs are costly and difficult to irrigate. We already use more water than we should, and as our summers get hotter the need for water will increase. Shouldn’t we be conserving as much water as possible? It’s time to debunk another green roof myth.
It is true that in the few first years of development, many green roofs need irrigation to help plants establish roots and mature. If you are installing an extensive roof, you can avoid costs and reduce the development period considerably by using pre-grown mats made offsite. If not, you will need some sort of drip irrigation or manual method (like a good old-fashioned water hose).
Luckily there is a myriad of ways to reduce the amount of water needed for irrigation. You can design thicker layers of growing medium that can absorb and retain more water, and install a water retention layer that can catch drainage. Using native plants, and plants that are drought resistant such as sedums can also help reduce water use. In addition, you can use water recycling methods such as grey water irrigation or collecting HVAC condensation. But even if a small amount of water is used for irrigation, it is just a drop in the bucket compared to how much water green roofs can save.
Denver Water did a study on Denver’s Green Roof Initiative and decided that there will there is no negative water impact. Most buildings are expected to have extensive green roofs that don’t need much irrigation. Also, the amount of water retained on green roofs helps the city prevent overflow during storm events.
Remember how we’ve mentioned that cities are getting hotter each year? Living architecture such as green roofs and green walls help mitigate urban heat islands, reducing the average temperature of our neighborhoods and our overall consumption of energy. It can also insulate buildings, further reducing the energy needed for heating and cooling. And energy production requires an astonishing amount of fresh water.
In fact, a study at Virginia Tech found that the amount of water needed to burn an incandescent light bulb for one year could be anywhere from 3,000 to 6,000 gallons (1). The natural gas extraction method most commonly known as “fracking” can use anywhere from 1.5 to 16 millions gallons of water per well depending on how they are managed (2). In addition to using an enormous amount of water, the fossil fuel industry is also responsible for negatively impacting the quality of water. Either from oils spills, extraction processes, wastewater from refineries, or groundwater contamination, the fossil fuel industry is a major water polluter (3). Decreasing our dependence on fossil fuels and reducing our energy consumption are great ways to conserve water and keep it clean, and living architecture is one of many ways to do just that.
That’s another green roof myth debunked! Stay tuned for more myth-busting in the future. Need help with your green roof project? Contact Sow Green today and let us give you a hand.