Modern green roof designs include a layer of vegetation planted over a waterproofing system typically installed on top of flat roofs or a slightly sloped roof, although the green roof concept can be applied to intensive roofs of any configuration, even on walls. In general, residential green roofs are much lighter and more straightforward with a modest roof load than those on large multistory buildings, including trees, and require minimal maintenance. While records of traditional sod roofs and rooftop gardens go back to 500 B.C.E., modern green roofs started becoming common in Europe, especially Germany, over 40 years ago with the layering system used today. The basic structure of the green roof layers consists of a variety of plants, several inches of growing medium (typically different than a layer of soil), filter membrane, drainage layer that provides aeration for plant roots, waterproof/root repellant layer, roofing membrane support for plantings above, thermal insulation, vapor control layer, and structural roof support. With a wider variety of plants come improvements in biodiversity (sometimes called brown roofs), management of stormwater runoff, and improved air quality by filtering pollutants in cities. As they become more popular in the U.S., green roof symposia, green roof professional training courses, and social groups are springing up in many areas.
Advantages Of A Green Roof System
The greater insulation offered by different green roof types can reduce heating and cooling; reducing energy consumption for air conditioning by 75% under some conditions, and provide heat gain in winter. With summer energy demands, going up the energy savings also extends your HVAC system’s lifespan and lowers greenhouse gas emissions overall. Large expanses of traditional rooftops have created urban heat islands that change the local air temperature and average temperatures as well, and green roofs can be part of the solution.
Green roofs reduce noise, especially from traffic in urban environments. A green roof can reduce the noise from outside by 40 decibels or more depending on the types of vegetation used.
Green roofs don’t catch fire from embers landing on them, as happens in parts of the country prone to wildfires.
Besides the environmental benefits, a green roof lasts longer because the layers of waterproofing membranes are protected from ultraviolet radiation, large temperature changes that can cause micro-tearing, and physical wear from falling debris by the roof surface. The life spans of residential green roofs may be more than double that of conventional roofs. Two examples of very durable roof gardens are the extensive green roofs of Rockefeller Center in New York City that have the same waterproofing membranes installed in the 1930s, and the Chicago City Hall green roof.
What Do I Need To Know For Install?
You will need to know the slope, the structural loading capacity, and existing materials of the roof structure, as well as the nature of any drainage systems, waterproofing, and electrical and water supply, and what kind of sun and wind exposure the roof gets. The climate is also an essential consideration for the design and planting. If you have hot, dry summers, drought-tolerant plants may be the best way to go, or if rainfall is sometimes extremely heavy but infrequent. In these cases, it may be necessary to have a thicker growing medium made of materials that can absorb large amounts of water and store it. Our roof design team experts at Blue Nail will review all the essential considerations for different roofs and give you the information you need to make an informed decision.
The cost of green roof systems varies considerably depending on considerations such as the depth of the growing medium, the types of plants, size of the installation, and use of irrigation. Plant selection drives the design. Choosing hardy plants to have limited plant diversity in the past, but a better understanding of plant life and plant growth has greatly expanded the number of plant species now used. A green roof installation with root repellent/waterproof membranes may be installed for $10-$24 per square foot. While green roofs typically require a greater initial investment, they can extend the roof membrane’s life and reduce the heating and cooling costs of your building. Please speak to one of our green roof professionals with experience in the green roof industry about the range of costs and benefits of different systems and designs of your green roof project.
The warranties on the building products used in green roof infrastructure are similar to those for all other building products in a home, but they must be installed according to the green roof manufacturer’s specifications.
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