What is a Green Roof?

Green roofs are far more than just a layer of soil and vegetation atop a building; they are living ecosystems that can support a diverse range of plant and animal species.

Green roofs are designed to provide both environmental and aesthetic benefits. Green roofs can reduce a building’s energy usage, extend the lifespan of HVAC systems, and reduce the heat island effect. Green roofs attract pollinators and provide a habitat for birds and insects. They also absorb sound rather than amplify it.

A green roof consists of several components, including a barrier to prevent water damage to the structure, a drainage system, filter cloth, a lightweight growing medium, and plants.

There are two basic types of green roof systems: extensive and intensive. The main differences between the two are soil depth, weight, cost, maintenance, plant selection, and function.

Extensive green roofs are simpler, utilizing hardy plants and a shallow growing medium; they require minimal structural support and little maintenance, and they are designed to be self-sustaining. Extensive green roofs place less of a load on the roof. They are typically less expensive to install and maintain than intensive green roof systems, usually needing only semi-annual inspections for weeds or damage.

Intensive green roofs are more complex and resemble a park setting with trees and shrubs, requiring structural support and ongoing maintenance, including irrigation, pruning, and replanting. The cost of annual maintenance will depend on the level of maintenance needed.

A conservative estimate for the life expectancy of a green roof is 40 years. The initial installation costs vary widely, depending on the type of green roof, the project’s size and scale, and your location.

There are several practical considerations to help you decide if a green roof is right for you.

• The slope of your roof
• Structural load capacity
• The existing materials on the roof
• Drainage systems, if any
• Waterproofing
• Access to electrical
• Wind and sun exposure

In some cases, the factors may align in a way that makes installing a green roof impractical.