Green Roofs and Water Mitigation

With more and more people turning to green living and making changes to their structures to accommodate such trends, we couldn’t help but write about green roofing. Also known by other names, including green roofs, oikosteges, vegetated roofs, and living roofs, this green roof is gaining newfound popularity even though it has historical roots.
First of all, what exactly is a green roof? It is a partially or totally covered roof with vegetation and a growing medium, planted on a waterproofing membrane. It is an extension of a roof above ground level, built on a man-made structure, which allows vegetation to grow in a growing medium and which is designed, constructed and maintained in accordance with a Construction Standard. The set includes, at a minimum, a root repellant system, a drainage system, a filter layer, a growing medium and plants. There are three types of green roofs: intensive, semi-intensive or extensive, with extensive self-sustaining for the most part.
The benefits of a vegetated roof are many and include absorbing rainwater, providing insulation, creating habitat for wildlife, and helping to reduce urban air temperatures. In addition, they provide excellent insulation and this helps to reduce the need for heating and energy consumption during the winter months, as well as cooling in the summer, both by 26%! Additionally, a green roof can help reduce stormwater runoff while filtering pollutants and heavy metals from rainwater. Plus, these ceilings are great for soundproofing! With the many layers that the green roof produces, sound waves are absorbed, reflected, or deflected. This is beneficial for the noise and sound of cars, trains, and people in a populated city.
As mentioned above, green roofs have a long history and “grass roofs” have been around in Scandinavia for centuries. Germany modernized the turf roof in the 1960s, and since then this style of roofing has spread to many countries. Green roofs are becoming increasingly popular in the United States, although they are not as common as in Europe. In Europe, Germany, Switzerland, the Netherlands, Norway, Italy, Austria, Hungary, Sweden, the United Kingdom and Greece are the main European countries promoting green roofs. The city of Linz in Austria has been paying developers to install vegetated roofs since 1983 and in Switzerland it has been a federal law since the late 1990s.
In the US, green roofs are making an appearance in Chicago, Atlanta, Portland, San Francisco, New York City and other cities. Construction of this type of environmentally friendly roof is recommended in cities where the urban heat island effect is a problem. The urban heat island effect describes the phenomenon when temperatures within a city are warmer than surrounding suburban/rural areas, primarily because urban development is built with materials that effectively retain heat. The urban heat island effect lowers air quality by increasing the production of pollutants like ozone, and lowers water quality as warmer waters flow into area streams, stressing their ecosystems.
As mentioned above, green roofs are great for water mitigation as they lessen the impacts of stormwater runoff. Vegetated roof systems can retain around 60-100% of the rainwater they receive, which is amazing! In areas with combined sewer and stormwater systems, severe storms can overload the sewage system and cause flooding. Flood damage is bad enough let alone when flood water carries raw sewage and deposits it into local waterways. Therefore, green roofs are an effective way to mitigate water.
For homeowners, green roofs help prevent flooding and water damage by decreasing the overall amount of runoff from rain and reducing the rate of roof runoff. It has been found that they can retain up to 75% of rainwater, gradually releasing it into the atmosphere through condensation and transpiration. Additionally, green roofs are a financial benefit as they dramatically increase the life of the roof.
Regarding the disadvantages of vegetated roofs, a higher initial cost of $15-$20 per square foot is probably the main disadvantage. Depending on the type of green roof, maintenance costs may be higher, but some types of green roofs have little or no ongoing cost. Living roofs also place higher demands on the structure’s waterproofing system because water is retained in the roof and because of the potential for roots to penetrate the waterproofing membrane. It is true that installing proper waterproofing systems and root barriers can increase the initial cost of the roof; however, due to the fact that this type of cover protects the waterproofing membrane from the elements, particularly ultraviolet light, the life expectancy of the membranes is doubled or even tripled, leading to recoup upfront cost differentials .
So what about living roofs and Florida? Currently, the largest living roof is located in Pensacola, Florida at the Escambia County One Stop Permit Center. The cover is more of an intensive type, compartmentalized by plant species. On top of that, green roofs are appearing more and more in Florida.
In short, green roofs are not only aesthetically pleasing to the eye, they also provide tremendous benefits for homeowners and the environment. With these roof options passing even hurricane wind stress tests, they are definitely providing homeowners with a roof option worth considering!