Green Roofs – The Best of Biophilic Design
Jim Mumford on the first permitted commercial green roof in San Diego County.
“The green roof is the only building element that improves with age!”
Also known as eco-roofs, vegetated roofs, or living roofs, a green roof is an engineered, lightweight roofing system supporting plants.
Green roofs on a building – whether on a small home or on an extensive commercial structure – are roofs partially or completely covered with vegetation, along with a growing medium. Green roofs are installed and planted over a waterproofing membrane. Green roofs often include additional layers such as a root barrier, drainage system, and irrigation system.
Green roofs are NOT glorified planter boxes. They are a far more sophisticated, carefully engineered element of your building. Green roofs sit on top of a man-made structure. Green roofs can exist at grade, below grade, or above grade.
A green roof does not have to be flat. Green roofs can accommodate up to a 40 percent slope. Each and every green roof is unique, and is engineeered, designed, and installed to your custom specifications and needs.
Green roof lifespan vs. traditional roof?
Green roofs result in extended life expectancy of a roof. Based on 50-plus years of experience with green roofs in Germany where green roofs are common, a green roof can be expected to experience double or triple the life of a standard roof.
How does this work? Green roofs provide protection of the waterproofing membrane from wind-blown debris, and shielding from damaging UV radiation which is increasing due to climate change. Green roofs provide impressive insulation from temperature extremes, thereby minimizing damage from daily expansion and contraction.
Because green roofs last longer, they reduce construction waste in landfills because they do not have to be torn down and replaced as often. There is also a cost savings over the lifetime of the building itself.
What are the benefits of green roofs?
Green roofs provide many benefits. A partial list includes:
- Controlling stormwater runoff, erosion and pollution, lessening the impact and cost of processing in sewage treatment plants and extending capacity.
- A green roof can hold 60 to 80 percent of a rain event. Water is released more slowly, helping to filter particulate matter out of water running onto landscapes and hardscapes.
- Water has more chance of running into the landscape as irrigation.
- Improving water quality
- Adds oxygen to the air
- Mitigates urban heat-island effects, cooling and cleaning the air
- Conserving energy
- Reducing sound reflection and transmission
- Reducing heating and cooling energy costs
- Creating wildlife habitats and biodiversity
- Reduces the spread of wildfires
- Increases the life of the roof, reducing landfill impact
- Can provide space for a rooftop farm
- Can provide habitat for pollinators
- When paired with solar panels, increases their overall performance by as much as 15 percent
- Improving the aesthetic environment in both work and home settings
This green roof design by landscape architect Glen Schmidt depicts the opening musical notes of “Ode to Joy” at Sharp Memorial Hospital in San Diego, California.
Where are green roofs possible? Can a green roof go on any building?
Your building’s structural load capacity must be determined when considering a green roof for residential or commercial application. Green roofs weigh more than a standard roof. Although it is not a major difference, you nevertheless must give careful consideration to the amount of weight your structure can safely hold.
A retrofitted green roof in Southern California is difficult, as an existing roof typically cannot bear the extra weight of a green roof as originally constructed.
Good Earth Plant Company must have an engineer’s stamp on the roof plans – no excpetions.
Other considerations include access to water, and the amount of sun and wind exposure the plants on your green roof will receive. In Southern California and similar arid climates, a green roof must be irrigated between April and November.
Shallow profile green roofs can be installed using a tray system, but this may not always be the best choice. Good Earth Plant Company can access multiple options for modular trays, as well as loose laid or plant-in-place systems.
Every green roof we plan and install is evaluated individually onsite in consultation with experienced, licensed roofers, so we can recommend the best solution taking into account cost and longevity.
Good Earth Plant Company specializes primarily in extensive green roof systems. This is a roof constructed with about four inches of growing media.
Can a green roof save costs over time?
An extensive green roof system may reduce a building’s cooling needs by 25 percent and prevent heat loss by 26 percent. This can be a substantial energy savings as every one degree Fahrenheit can reduce electricity use for air conditioning by eight percent.
Green roofs also make significant contributions to a building’s LEED rating, with as many as 15 credits available depending upon design and level of integration with other building systems.
While green roofs are the single component of a building that improves with age, remember that maintenance is a critical part of its success.
