Green roofs can provide environmental benefits that include increasing building insulation, reducing building absorption and heat retention (in what are known as urban islands), adding aesthetic value, reducing runoff and rainwater in urban environments, improving air quality by removing pollutants, and cooling photovoltaic panels to improve Its function is to provide a habitat for flowers.
Until very recently, improvements in green-roofed environmental services were largely achieved. In recent years, ecologists have increased their involvement, applying ecological theory to enhance biodiversity, and selecting specific plant groups to perform roles such as sequestering carbon and providing cooler surfaces.
In this article, we try to summarize in some detail the benefits of green roofs.
Although installing a green roof usually involves higher initial costs than a traditional roof, there are many economic benefits that can make up for it. An increased R-value (a measure of a material’s resistance to heat flow) for a roofing system, combined with lower roof temperatures, reduces HVAC loads, resulting in energy cost savings. A green roof may improve real estate value and marketability, especially in urban areas with small green spaces. The University of Michigan conducted an evaluation study comparing a 2,000 square meter traditional roof and a green roof. The study looked at a range of benefits of green roofs including rainwater management, improved health benefits due to reduced pollution, and energy savings. Over its estimated 40-year lifespan, a green roof will save approximately $200,000, nearly two-thirds of which will come from reduced energy costs. However, the economic benefits of any single green roof will depend on its design, geographic location, surroundings, and the building itself.
A green roof also helps control and retain stormwater runoff. The increasing urbanization of towns and cities has reduced green spaces and increased impermeable roofs. Precipitation generally flows from the roof of the building to the sides and vents in the roof and flows into storm drains. From storm sewers it either enters a municipal water treatment facility, or is deposited directly into the ecosystem via lakes, streams, and rivers. The water picks up any dirt or contaminants on the surface and is flushed out into storm drains as well. In cities with a combined sewage flow system where rainwater runoff, domestic sewage, and industrial sewage are collected in the same pipe for treatment, too much rainwater can cause the city sewage system to overflow, leading to sewage discharges in Streams and rivers. A green roof can help prevent this by retaining water in plants and the growth medium, thus slowing down and reducing the amount of stormwater entering the ecosystem, thus reducing flooding and erosion. Data collected from a study conducted by researchers at Penn State University’s Green Roof Research Center shows that green roofs absorbed up to 80% of precipitation during rainstorms, compared to the 24% typical for standard roofs. As green roof plants mature and root systems grow, rainwater retention may increase. In some cities, buildings with green roofs may qualify for reduced stormwater management fees because green roofs reduce the amount of rainwater leaving the site. Growing medium and roof plant material also act as a filter and help neutralize acid rain, trapping dust and airborne particles.
Reducing rooftop temperatures and improving air quality
The temperature in cities is often higher than in the surrounding countryside, a phenomenon known as the urban heat island effect. Large amounts of paved surfaces in cities absorb solar radiation and re-radiate it as heat, increasing the local air temperature. For example, during the summer months in New York City, the average daily minimum temperature is -13°C warmer than the surrounding suburbs and rural areas and even more so during heat waves. Green roofs not only help reduce the urban heat island effect by covering traditional dark rooftops with plants that absorb less heat, but also use solar radiation to evaporate water from growing medium and leach (water uptake through plant roots and release through leaves as steam) moisture of plants. This evaporation process lowers the surface temperature by using the heat of the air to evaporate the water.
A darker heat-absorbing roof surface increases the demand for mechanical systems, making it more difficult to cool the building adequately, while a green roof lowers the surface temperature, thus lowering the temperature of the building itself. Additional layers of the green roof also act as insulation. This reduces the amount of heat that passes into the building, reduces cooling loads, and provides some insulation during the heating season, although it is important to note that it does not replace the need for additional thermal insulation. The benefit is greater for buildings with a higher surface-to-wall ratio (ie, buildings with greater surface area versus outer wall area). Additional layers of the roof and growing medium also help reduce internal noise from mechanical equipment on the roof.
Improving the efficiency of mechanical equipment
Cooler roof temperatures generated by a green roof help enhance the efficiency of rooftop mechanical equipment by making rooftop air cooler. When in cooling mode, HVAC equipment must pre-cool the outside air to reach the desired temperature. If the air on the roof is made cooler by a green roof, this process is easier and consumes less energy. Therefore, lower rooftop air temperatures improve the efficiency of rooftop HVAC appliances that reject heat because they operate at a lower ambient temperature.
Reduce greenhouse gas emissions
Reducing cooling loads also helps reduce greenhouse gas emissions from fossil fuel combustion associated with the use of HVAC equipment. Adding plants and trees to the urban landscape increases photosynthesis, which reduces the levels of carbon dioxide produced by vehicles, industrial facilities, and mechanical systems. It also increases oxygen production.
Extend the life of the roof
A green roof can increase the life expectancy of a roofing system by protecting the roofing material from direct UV rays and temperature extremes. As a result, the roof structure can require less maintenance, saving the owner money in replacement costs over the long life of the roofing system. A well-maintained green roof can more than double the number of years before a roof needs replacement compared to a standard roof, offsetting some of the additional costs of installation.
Would you like to be part of the story?
We in Schaduf envision a more sustainable Middle East, and we cannot do this without “faith.” If you believe in our philosophy of creating sustainable cities, and believe that the green roof plays a significant role, then be part of the story.