The building and construction industry is the leading producer of pollution worldwide. That’s not an award the industry is particularly proud of, and construction companies have been working to reduce carbon emissions over the decades. Practices like sustainable and green building materials, construction machinery that runs on different power sources, and one of the most interesting and often-overlooked method: the green roof.

While green roofs can be installed and maintained in just about any project – from residential homes to office buildings – they’re especially useful in urban commercial spaces.

What is a Green Roof?

A green roof is any roof that has been intentionally designed to include a substrate layer that can support the growth of vegetation. Another aspect is the amount of rooftop square-footage covered. A typical green roof will cover 80% or more of the roof’s surface. Starting a green roof isn’t simply scattering potted plants across your standard roof. Most modern green roof systems are composed of a:

– waterproof membrane

– root barrier

– drainage layer

– water retention layer

– fabric filter

– substrate/growing medium

– vegetation

Types of Green Roofs

There are three basic types of green roof to choose from, ranging in complexity of care and maintenance needed. The primary differences are substrate depth, type of vegetation supported, and maintenance required.

Extensive: This type of green roof is generally designed to be as “hands-off” as possible. It’s a great choice if your building’s roof is difficult to access or serves no other purpose. The ideal plantings for an extensive maintenance roof include native plant species – especially those that are self-sustaining and capable of weathering conditions like frost, drought, and lower nutrient levels. These are lightweight, with a soil depth rarely more than 6” deep.

Semi-intensive: These roofs require more upkeep than an extensive green roof system, but can include a wider variety of plant species. Soil depth for this type of roof ranges 6”-12” deep.

Intensive: You might want to hire a maintenance team for this. Intensive green rooftops require frequent maintenance, but open up a nearly unlimited variety of plants that can be grown. These are the types of green roofs that sustain urban rooftop gardens and fruit-bearing trees. This is especially true of plants with more specialized growing conditions, like shrubs and small trees. The soil depth for these typically ranges 12”-36” or more, depending on the plants’ needs.

With the proper maintenance and installation, all three of these roof types can survive and thrive in an urban environment.

Benefits of Green Roofs in Urban Areas

There are many benefits to installing a green roof atop a commercial building in a busy urban area. Both the building owner and the surrounding community can reap the rewards without a significant change to every day life.

Stormwater Mitigation & Reduced Risk of Urban Flooding

Think of a green roof as a sponge. Its permeable soil and water retention layer absorbs water and stores a portion or all of that water for later use. Current data shows that even the most “hands-off” green roof (extensive) is capable of reducing stormwater runoff all the way up to 100% during any given period of rainfall!

The retention helps reduce a building’s stormwater management costs, as well as slow the runoff rate overall. Green roofs have the ability to reduce flow rate that delays runoff by up to three hours, meaning the strain on municipal sewer systems and the potential for urban flooding is lessened.

Improved Urban Water Quality

Stormwater mitigation goes hand-in-hand with the next benefit: improved urban water quality. With the various layers of a green roof – specifically the substrate – runoff is naturally filtered, removing heavy metals, large particulate matter, and various other debris before the water makes it into the municipal sewer system or urban waterways.

Since certain contaminants are already filtered out through the green roof system, the process makes it easier, and less expensive, for cities to treat water for public use. When implemented at scale, green roofs help keep the costs of municipal water down – improving water quality and saving commercial properties money on monthly utility bills.

Passive Cooling

Energy-efficient buildings are more attractive to communities as well as potential tenants. Constructing a sustainable building with sustainable building materials is a big step toward creating goodwill, showing an intent to make conditions surrounding the building better.

A noticeable benefit to green roofs on urban commercial properties is this energy efficiency. The green roof provides an added layer of thermal resistance, preventing solar heat transmission through the rooftop materials. In turn, the building and its tenants rely less on expensive HVAC systems for heating and cooling indoor spaces, lowering operating costs and reducing greenhouse gas emissions. Instead of the expensive, expansive system in the picture, choose a green roof.

Implementing a green roof reduces city-wide air conditioning demands and saves commercial properties money on utilities, as well as reducing profit loss from power outages or rolling blackouts or brownouts which can halt business operations.

Combat Urban Heat Island Effect

First, what is the heat island effect? The heat island effect is the effect of urban areas experiencing higher average temperatures than rural areas. The effict is caused by the excessive distribution of dark-colored surfaces, in addition to high concentrations of concrete, steel, and other solar energy-absorbing building materials. That heat is then radiated to the local environment.

Green roofs reduce this phenomenon via evapotranspiration, a natural process in which plants absorb water from soil through their roots, eventually releasing it as water vapor through the microscopic pores of their leaves. During the evaporation process, water absorbs heat from the air and helps reduce the heat island effect. Combine this process with plants’ natural ability to reflect solar energy, and temperatures can reduce by up to 5 degrees Fahrenheit, according to the EPA. Eliminating or significantly reducing the heat island effect also helps decrease the likelihood of heat-related illnesses and deaths.

Reduced Ambient Noise

The thermal insulation offered by green roofs does wonders for occupant comfort as well as a building owner’s bottom line. In addition to thermal insulation, green roofs also function as acoustic insulators, helping to reduce ambient noise in a building’s upper floors. Green roofs have been found to be more efficient at reducing noise than traditional roofs – even without ceiling insulation!

Green roofs are able to effectively block a wide range of noise frequencies. Plants abosrb higher frequencies like sirens, small vehicle motors, and car alarms, while the dense, permeable growing medium blocks the lower frequencies of large vehicle engines, construction equipment, airplanes, and more.

Keeping out unwanted noise results in fewer distractions, leading to increased productivity and increased user satisfaction.

Longer Lifespan

A properly installed and maintained green roof has a double the estimated lifespan than their traditional counterparts. Green roofs can last up to 40 years, while a traditional roof last less than 20. The vegetative layer protects the underlying roof structure from the elements and reduces the damaging effects of thermal stress on building materials.

The extended lifetime helps commercial properties save money on replacement materials, lowers the building’s overall embodied carbon, and minimizes construction waste.

Improved Occupant Health

Sustainable building practices and materials have been shown to have positive effects on the physical and mental health of the occupants of a building. Unfortunately, urban areas have a relatively low percentage of green space, mainly due to poor planning and overdevelopment. Implementing a green roof in an urban commercial setting provide a convenient means to increase a city’s overall square footage of green space.

Humans are drawn to the natural environment, a phenomenon known as biophilia, suggesting that humans have a genetically-determined affinity to interact with the natural world. Having access to green space in urban areas feeds this need, and by including it in your building’s design you can help increase health and happiness, and in turn increase worker productivity of building residents as well as nearby building occupants.

Including a green roof may also provide opportunities for a restful, relaxing environment that allows occupants to go outside for some fresh air and sunlight during breaks.

Urban Agriculture

Agriculture doesn’t have to be limited to open, rural farmland. Local, farm-to-table choices have become something people look for when they choose produce and meat at the grocery store. Knowing your food came from within a few miles of home means its fresher, and likely grown more sustainably and with fewer (or none at all) chemicals that enhance or preserve freshness for shipping longer distances.

But urban areas may still suffer. Green roofs on urban commercial buildings offer a chance for residents to reap the rewards of the farm-to table concept. By installing an “intensive” green roof, you make way for the ability to grow fruits and vegetables and offer access to local, healthy options. Some businesses may choose to use the crop internally, supplying break rooms and kitchen spaces with healthy options, while others may choose to sell or donate to the community. No matter which option you choose, your produce will benefit your building by the above reasons, as well as offering offering fresh food options for those that may not typically have access.

Increased Property Value & Marketability

A well-maintained, aesthetically-pleasing green roof will undoubtedly increase the overall value of urban commercial properties, as well as improve their marketability. Tenants and customers looking for sustainability will likely choose a building or business with sustainability at the forefront – like the inclusion of a green roof – will patronize that building before one that does not include such sustainable features.

This especially applies to urban buildings in spaces were green space is otherwise unavailable or limited, since it provides a valuable amenity and asset the community is lacking.

Maintenance of Your Green Roof

In the beginning, we spoke about what a green roof is, the types of green roofs, and their maintenance needs. There’s more to just installing a green roof and checking on it now and then (depending on the type you choose).

In the Beginning

Water the green roof’s soil and vegetation during the first 18 months, as well as during extreme drought conditions. Even your drought-tolerant, native plants can suffer in extreme conditions.

Sparingly fertilize the plants of your green roof only during the establishment period. Keep in mind your green roof is a stormwater management tool, and you don’t want excess nutrients leaving the roof!

Seasonal Maintenance

When you first install your green roof, you’ll want to regularly check for weeds and invasive plants within the first 18 months of growth. After plants are established and maintaining healthy growth, you want to check in at least every 6 months, or when a significant seasonal weather change occurs.

Make sure to inspect drains and remove any blockages. If water isn’t draining properly, the benefits discussed above are not maximized to their full potential. Additionally, standing water can attract insects and other pests.

Annual Maintenance

Just as you may annually inspect systems like HVAC, electrical, and the like inside your building, your green roof needs annual maintenance as well. Your annual maintenance checklist is, of course, the entire system. Make sure to take extra care with the following:

– Irrigation system (if present)

– Plants: add or replace as necessary for at least 80% coverage on commercial rooftops

– Take a soil sample and send it out for testing

Not all green roofs have an irrigation system, and rely on landscape companies to service them. Irrigation systems designed specifically for commercial green roofs are available and a good investment over time.

Final Thoughts

Take the next step in spreading goodwill around your urban commercial building. Whether you plan to make a green roof part of your design plans from the beginning, or are interested in installing a green roof on your existing building, the staff at Structr Group can help.

We’ll help you determine which type of roof is best for you and your needs and help you implement it in the best, easiest way possible.

Contact us today!