- What is a green roof and how do they work?
- Green Roof Benefits
- Problems and Disadvantages of Green Roofs
- Estimating the Environmental Effects of Green Roofs
- Types of Green Roofs
- Green Roofs vs. Cool Roofs
- Best Plants for Green Roofs
- How do you install Green Roofs?
- Costs of Installing and Maintaining Green Roofs
- 10 Beautiful Greem Roofs across the US [+ Gallery]
- How do Green Roofs support Pollinators?
What is a green roof and how do they work?
According to GreenRoofs.org, a green roof is an extension of an existing roof that you may see on any building, but it involves high-quality waterproofing, a root repellent system, a drainage system, a filter cloth, a lightweight growing medium, and plants. Green roofs in urban cities all over the world have a variety of tangible and intangible benefits that positively affect our communities and environment.
Green roofs consist of multiple layers on top of a building, including vegetation, growing medium, filter membrane, drainage layer, waterproof/root repellant layer, roofing membrane support for plantings above, thermal insulation, vapor control layer, and structural roof support. Each of the layers plays a crucial role in not only protecting the building they are on top of but also supporting the greenery that grows there.
Green Roof Benefits
Green roofs provide a variety of benefits for structures, the environment, and the communities that host them. Simply put, green roofs are beneficial in an economic, social, and environmental sense, and these benefits include:
- Increased Roofing Membrane Durability: Similar to any roof, an increased presence of rainwater can lead to a deterioration of the roof over time, but with a green roof, the added layers help decrease the exposure of waterproofing membranes to large temperature fluctuations, which can cause micro-tearing, and even ultraviolet radiation. Ultimately, green roofs help ensure that the cost of repairing these structures over time remains low.
- Fire Retardation: With lush vegetation present on rooftops, there is an opportunity to design green roofs that are fire-resistant. While fire retardation is not guaranteed, experts recommend incorporating 60% of a roof’s vegetation from the sedum family of groundcover plantings. It is also important to note that creating green rooftops with moss or grasses has a tendency to dry out, which can lead to a potential fire hazard.
- Certifications: For businesses looking to strengthen sustainability initiatives, green roofs prove to be a valuable investment. Having a green roof can lend itself to a variety of LEED credit categories, including energy and atmosphere, water efficiency, and materials and resources.
- Waste Diversion: A green roof can help deter additional waste from landfills by giving a longer life to the waterproofing membranes. There are even opportunities for businesses to create green roofs with recycled materials.
- Stormwater Management: Thanks to the multiple layers and the vegetation on green roofs, rainwater becomes more retained and the possibility of stormwater runoff reduces as well.
- Moderation Of Urban Heat Island Effect: Simply put, plants help cool down our cities during those hot summer months and can even decrease the amount of CO2 we’re putting into the air.
- New Amenity Spaces: For businesses and residential spaces, transforming your rooftop from gray to green even offers a new space for your community to engage with each other without having to exit the building itself.
- Local Job Creation: With a new vegetation space comes the need for more talented individuals who know how to effectively maintain it. Green roofs help create jobs relating to manufacturing, plant growth/maintenance, and more in local communities.
- Noise Reduction: According to LivingRoofs, green roofs with a 12 cm substrate layer can reduce sound by 40dB and one of 20 cm by 46-50dB, but the level of noise reduction is dependent on the depth of the overall system.
- Urban Agriculture: Green rooftops help make our cities more resilient, and even present innovative ways to grow food. Growing specific plants on urban rooftops even aids the pollinators, DNA samples collected from Best Bees honey have shown that urban bees pollinate eight times more species than suburban bees. Urban beehives have higher winter survival rates and produce 56% more honey than their country cousins.
- Educational Opportunities: When people see greenery on what would otherwise be a gray rooftop, they want to know more! Green roofs provide an excellent opportunity to engage and educate communities on the impacts of strategic vegetation in our cities.
- Aesthetic Improvements: Incorporating a green roof into our urban cities is easy on the eyes, too. Did you know that the simple act of viewing additional greenery throughout your day can help boost your mood by reducing stress and sadness levels?
- Energy Efficiency: Thanks to the insulation of green roofs, temperatures within buildings are regulated which ultimately reduces the amount of energy needed to cool buildings down in the summer, and keep them warm in the winter.
- Reduction of Electromagnetic Radiation: Many large cities contain electromagnetic frequencies, and experts believe they can have a multitude of effects on the human body. Since green roofs have been found to help block most incoming electromagnetic radiation, switching from gray to green can have a positive impact on our overall health, too.
- Increased Biodiversity: Green rooftops are crucial elements of our cities’ biodiversity, and installing these vegetated roofs help pollinators as well.
Problems and Disadvantages of Green Roofs
While the advantages of green roofs are extensive, there are various disadvantages that everyone should be aware of before installing one on their rooftop. While the impact of green roofs includes lowering costs for certain aspects like energy use, there is a substantial cost of having these roofs installed. According to Hunker, green roofs are heavier than roofs without any added layers of vegetation, which may mean that some buildings require additional support.
Green roofs will also require more maintenance than a roof that does not contain any greenery, which would lead to an increase in the overall investment in the roof and additional team members needed to take care of it.
Finally, one major disadvantage of green roofs includes the limited variety of plant options that are available in certain areas. Depending on the type of system your green roof has, there may only be a small selection of plants that your green roof can accommodate.
Estimating the Environmental Effects of Green Roofs
In a 2018 case study about the city of Kansas City, Missouri, the Environmental Protection Agency found that “green roofs can contribute to environmental and livability goals—to mitigate the urban heat island effect, maintain clean air and water, and lower energy costs in buildings—while greening the urban landscape.” This furthers the data and expectation that green roofs are not only helpful for our communities, but they will soon be vital in helping our cities thrive.
Types of Green Roofs
Green roofs are typically broken down into two categories, and each varies in the types of buildings they are hosted on and the plant species that are present.
- Extensive: Also referred to as “low profile” or “performance”, these green roofs are often the simplest to install, and are commonly found on residential properties. Planting for extensive green roofs “ranges from 1.6 to 6 inches deep and while deeper systems have been installed they are not favored as much as the shallower systems.”
- Intensive: Contrary to extensive roofs, intensive green roofs are most commonly installed on larger rooftops where a wide variety of vegetation can be found. These types of green roofs do require more weight and a deeper system build-up, which also leads to an increased need for regular maintenance due to their deeper growing medium.
Green Roofs vs. Cool Roofs
Green roofs should not be mistaken for cool roofs, as the two have different methods for positively impacting the environment. Drawdown notes that while both reduce building energy use for heating and/or cooling, green roofs use soil and vegetation as living insulation, and cool roofs reflect solar energy.
Best Plants for Green Roofs
When planting for a green roof, it’s important to remember which type of green roof system is being installed. An intensive green roof (commercial buildings) often contains a deeper soil medium, which means larger plant groupings like vegetable and herb gardens, shrubs, and even trees. Below is a list of ideal plants for intensive green roofs from Green Roof Guide:
- Gold sedum (gold moss or sedum acre): an incredibly hardy, drought-tolerant evergreen perennial that forms a mat of bright, beautiful yellow flowers.
- White stonecrop (sedum album): a herbaceous perennial with a sprawling growth habit. Perfect for spreading a lightweight covering on a rooftop.
- Widow’s Cross: an annual (or evergreen) perennial with attractive pink and light green stems.
- Two-Row Stonecrop (Sedum Spurium): a mat-forming sedum that creates a carpet of reddish-hued flowers in the later summer months.
- Birdsfoot Trefoil: A member of the pea family with beautiful yellow, slipper-like flowers.
An extensive green roof (residential buildings) tends to contain a more shallow soil medium, so you’ll likely find drought-tolerant sedums (succulents) and grasses since they require less water and care. Below is a list of ideal plants for extensive green roofs, courtesy of Land8 Media:
- Sedum sarmentosum: a clear-green species known as “gold moss stonecrop”
- Sedum spurium: a perfect groundcover that can grow in any soil type
- Sempervivum: a succulent perennial plant with about 40 species
- Carex flacca or Carex glauca: also known as blue sedge
- Carex elata “Aurea”: commonly known as “bowles’ golden sedge”
How do you install green roofs?
For commercial spaces that are looking to have a green roof installed, we recommend working directly with a green roofing company to determine the costs, impact, and maintenance required. Below is a list of green roofing companies across the United States that help commercial businesses turn their rooftops from gray to green:
- Columbia Green Technologies: A global leader in the green roof market industry that is dedicated to “creating a positive environmental and social impact by building vibrant healthy cities for people to live, work and play.”
- Siplast: “The only commercial manufacturer to offer a roof system package that combines SBS-modified bitumen membranes with the added benefits of lightweight insulating concrete. Siplast installs commercial roofing systems across North America.
- Sempergreen: Installs green roofing systems, living walls, and green ground covers nationwide.
- LiveRoof: Has installed more than 10.3 million square feet of green roofing systems, and operates in 11 countries.
- GreenRise: Installs green roof and stormwater management systems on commercial buildings throughout the United States.
Costs of Installing and Maintaining Green Roofs
Depending on the type of green roof, homeowners and building owners should consider the cost of installing and maintaining these rooftops. The EPA states that the estimated costs of installing a green roof start at $10 per square foot for simpler extensive roofing, and $25 per square foot for intensive roofs. Annual maintenance costs for either type of roof may range from $0.75 to $1.50 per square foot.
10 Beautiful Green Roofs across the US
Searching for inspiration for your home or building’s green roof? Here are 10 of the most beautiful green roofs found in the United States.
How do green roofs support pollinators?
Our communities aren’t the only ones who benefit from the installation of green roofs throughout cities–these strategic initiatives help support pollinators in more ways than one.
- Safe Habitat: Green roofs provide a safe space for pollinators thanks to their naturally cool and biodiverse settings, and are also helpful in making up for ecological habitat fragmentation.
- Food: Bees are extremely important for our entire ecosystem to function, allowing over 80% of plants to reproduce through pollination. If the food sources for these pollinators were to disappear, it would cause an entire chain reaction of the food chain to suffer. If the pollination process declines or altogether disappears, we have the potential to lose plants, food for humans, animals, and even birds who depend on plants to survive. The incorporation of green roofs that have herb and flower gardens can greatly impact the health of pollinators nationwide.
Q: What is a green roof?
A: a green roof is an extension of an existing roof that you may see on any building, but it involves high-quality waterproofing, a root repellent system, a drainage system, a filter cloth, a lightweight growing medium, and plants
Q: What is the difference between an intensive and extensive green roof?
A: Intensive green roofs are typically installed for commercial buildings and have a deeper soil medium, whereas extensive green roofs are installed on residential homes and have a more shallow social medium/fewer maintenance requirements.
Q: What are the benefits of green roofs?
A: Green roofs are beneficial in an economic, social, and environmental sense. The installation of these roofs helps lower building temperatures, create local jobs, divert waste from landfills, and even protect pollinators.
Q: How much does it cost to install a green roof?
A: The EPA states that the estimated costs of installing a green roof start at $10 per square foot for simpler extensive roofing, and $25 per square foot for intensive roofs.
Green Roofs + Beehives Webinar
The benefits of green roofs are well established: they reduce the urban heat island effect, reduce stormwater runoff, aid in energy conservation, and help reconnect us to the natural world. When you add beehives to pollinate a green roof installation, these living roofs do even more. Together they promote wellness and build a community for tenants, cities, and the environment.
To learn more about how developers, designers, and building owners can put their urban rooftops to optimal use as part of their wider sustainability plans, register for The Best Bees Company free webinar with Columbia Green Technologies on Thursday, April 21st at 1pm EST.