If you’ve recently been in America's heartland and thought that it seems growingly more desolate, you’re not imagining things. You’ve witnessed something that is becoming a global trend: Populations are increasingly moving from rural to urban centers.

The United Nations estimates that three million people move to cities every week. And, whereas 30 percent of the world population lived in cities in 1950, that number has swelled to 55 percent today, with experts predicting the number to reach 68 percent in the next 15 to 30 years. (“68% of the world population projected to live in urban areas by 2050, says UN”)

Commensurate with this physical shift has been the forfeiture of natural landscapes. As the need for new buildings, roads, and various utilities increases, there are the natural landscapes and resources that are sacrificed to meet these demands.

There is hope for—and a path to—more sustainable practices in urban development.  In recent years, there has been increased focus in creating green spaces for some of the most densely populated environments across the U.S. One such method is the creation of green roofs to replace lost natural landscapes. These roofing systems provide a pleasing aesthetic alongside critical environmental benefits, including storm water management, thermal resistance, noise dampening, pollution control and increased biodiversity. By shielding green roof membranes from harmful UV rays and thermal shock, these vegetated roofing systems prolong the service life of the roofing and insulation systems.

 This “green” movement is also financially supported, with potential tax breaks offered for certain levels of LEED certification. These incentives offer one more potential benefit of green roofing, on top of the positive impacts on environment and emotional wellbeing.

Whatever your motivation may be to construct a green roof, you understand that a successful project requires deliberate planning, using the right products, and pinpoint assembly to ensure performance and system integrity. Here are some things to keep in mind when developing your green roof:

Design considerations

Not all green roofs are created equally. A roof system designed for maximum stormwater absorption can differ from one used as a daily recreational space. Therefore, deciding the intended use and purpose of your green roof are essential steps early in the process to save time and money. Considering that a green roof is a large planter, it is important to provide a sustainable environment for plant selection. This includes growing media type and depth, drainage or moisture retention, an initial and renewable organic content, and occasional maintenance.

Assembly types

There are several types of green roof assemblies, each designed for a specific roof application and selection of vegetation.

• Extensive: Designed to support a range of drought-tolerant plants that are self-sustaining and require minimal maintenance.
• Intensive: These are garden-like assemblies that may weigh up to several hundred pounds per square foot and are limited by the load-bearing capacity of the underlying structure.
• Semi-intensive: A cross between an extensive and intensive assembly, semi-intensive assemblies fall into a growing media depth range of six to twelve inches with plants that include ground covers, herbaceous plants, and select prairie plants, among others.
• Combination designs: These designs segment the roof area with localized and segmented combinations of the above types.
• Specialized designs: These are typically climate-specific designs that accommodate extreme climates, such as desert or tropical environments, that require specialized growing media and vegetation.

Components

It all starts with waterproofing. Choosing the appropriate waterproofing product is critical to maintaining a dry interior and a solid foundation for everything, up to the plants. From the deck up, assembly components may include: a waterproofing membrane, root barrier, insulation, filter fabric, drainage, or water retention course, growing media, erosion mats, and vegetation. Additional accessories may include edge metal, inspection chambers (for drains), pavers (for walkways), and ballast stone (for fire breaks between the vegetation and the building). The components are assembled to provide the intended space and to support the viability of the foliage.

Installation

Working with a qualified installer(s) is essential to ensure a successful green roof project. In some instances, such as an intensive green roof, it is common to use one installer for the membrane and another one for the vegetation. Depending on the intended use and complexity of the assembly type , a landscape architect may also be employed to choose the vegetation and design the layout of the plants. Every step following the waterproofing installation must be carefully monitored to preserve the watertight integrity of the waterproofing membrane.

Quality Assurance

The primary function of roofing is to prevent water ingress. Confirming that the waterproofing installation is sealed, then protecting the membrane from the installation process of all the assembly layers to follow, is crucial. Several methods may be employed to QA/QC the membrane's watertight integrity, including flood testing and Electronic Vector Mapping (EVM). Depending on the deck type, membrane type, and complete assembly, a 'leave behind system' will afford an opportunity to confirm the continued watertight integrity of the system after all the components and vegetation are placed.

Vegetation

Sedums (a perennial succulent) are the typical choice for an extensive green roof and are often used as a filler plant on these types of systems. They are well suited to the roof environment in a wide geographical area covering many hardiness zones. There are specific delivery, storage and handling considerations that you should observe to ensure the survival and successful growth of your roofing vegetation. Consult your installer to discuss favorable planting times, media placement, watering, installation, irrigation, and maintenance. It is not simply planting the desired vegetation but taking the necessary steps to ensure that it thrives in your unique environment.

Experience Counts

With so much invested in your green roof, choose a provider and applicator that understands the challenges and offers solutions with demonstrated successes. CETCO has been in the waterproofing industry for over 75 years, earning our first waterproofing patent in 1942. Our quality materials protect thousands of structures worldwide, including plaza decks, rooftop planters and earth-covered structures.

CETCO GREENSCAPES® Green Roof System is an all-in-one assembly that includes everything from waterproofing components to plants. It integrates cleanly with existing roofs—which is not commonly found with other providers—valuable time and money savings that look good on any bottom line. Incorporating COREFLEX® thermoplastic waterproofing membrane with its Active Polymer Core (APC) delivers durable waterproofing performance that establishes a critical foundation for any green roof project.

GREENSCAPES® and COREFLEX® are registered trademarks of Minerals Technologies Inc. or its subsidiaries.

Reference

“68% Of the World Population Projected to Live in Urban Areas by 2050, Says Un | UN Desa Department of Economic and Social Affairs.” United Nations, United Nations, 16 May 2018, https://www.un.org/development/desa/en/news/population/2018-revision-of-world-urbanization-prospects.html.