What does it mean to have a green roof? A green roof is any roof with a layer of vegetation over it. Green roofs can be extensive or intensive. Extensive green roofs usually focus on low growing plants and a thin layer of soil and are lower maintenance. Intensive green roof plants focus on deep plantings with a diverse ecosystem and increased maintenance. There are many considerations to look at before you install a green roof, here are a few of them.  

What to Plant 

Weather, irrigation accessibility, and maintenance play a major role in choosing what plants will thrive best on a green roof. In extensive green roofs, spread and hardiness are the most important qualities for a plant. Vegetation on an extensive green roof is built to be self-sustaining and requires less supervision than plants on an intensive green roof.  

Plants on extensive green roofs have low height and spread rapidly, such as succulents. Grasses are also often used on extensive green roofs but may need more maintenance. Because extensive green roofs have a thin layer of soil, they cannot accommodate larger and more diverse plants with more varied needs. Plants on intensive green roofs can be more varied because they have fewer limitations than extensive green roofs. An intensive green roof allows for deeper growth with more variety because they can accommodate more diverse species. However, intensive green roofs can come with some weight challenges because the building must be able to handle the additional weight of deeper plantings. 

Benefits and Cost of a Green Roof 

There are many environmental advantages of green roofs, specifically their ability to block solar heat and reduce the energy costs associated with building cooling. Green roofs can reflect and absorb solar energy, creating a more energy efficient building. According to the EPA, Green Roofs reduce building energy use by 0.7 percent on average which results in a reduction of cost by 23 cents per square foot of the surface of the roof annually.  

In addition to the energy benefits of green roofs, they can facilitate improved air quality and reduce greenhouse gas emissions due to additional vegetation. Green roofs also aid in stormwater runoff management by reducing runoff and increasing water quality through filtration techniques.  

Green roofs also provide aesthetically pleasing vegetation and can help reintroduce nature into urban landscapes and attract tenants.  However, while Green Roofs can reduce energy costs, installation and maintenance can be expensive.  

“Installing a green roof could cost you anywhere from three to five times more than the cost to put a new roof on,” states Michael Bare, VP and Head of Production with Roof Partners.

Bare explains that the cost is much higher than a traditional roof because you have to install a traditional roofing system and then the green roof system on top of it with an irrigation system of some kind as well. With commercial roofs, property owners have to put some type of maintenance plan in place. Traditional roofing systems only require maintenance around twice a year with a small crew, but green roofs require landscaping and roof maintenance with a much larger crew around twice per month. The associated maintenance cost of green roofs certainly adds up over time.  

Rooftop Garden Alternative 

A rooftop garden is a system of plants in containers or beds instead of directly on the surface of a roof. Both rooftop gardens and green roofs are environmentally beneficial, however, rooftop gardens have much lower installation costs. Additionally, green roofs can provide benefits that rooftop gardens cannot. For example, green roofs reduce energy costs by blocking solar rays and providing an extra layer of insulation.  

Rooftop gardens also provide more tenant engagement possibilities like allowing tenants to use beds for personal gardening activities or creating educational events.  

Potential Applications 

Aesthetically pleasing and environmentally conscious buildings are attractive to tenants concerned with environmental sustainability. Green roofs provide energy saving benefits, insulation, better air quality, and more. However, while green roofs can provide energy efficiency and additional green space, they can be costly to install and maintain. Green roofs and rooftop gardens can potentially benefit other populations like bees. If pollinator friendly plants are intentionally placed in these designated green areas, bees and other pollinators can benefit from urban landscaping.  

Different types of green roofs like extensive or intensive green roofs can provide ecological benefits like filtering stormwater runoff. Green roofs can filter stormwater through natural vegetation and can aid in stormwater management and maintenance. Roof top gardens might be the alternative for you if you’re looking for added green space for tenants with the aesthetics and functionality of a green roof without the added costs.  

To stay up to date on news and resources such as this and other topics of importance to the real estate industry, subscribe to the free CRE Insight Journal Newsletter using this link. 

Sources:  

• Michael Bare, VP and Head of Production, Roofing Partners LLC
• Using Green Roofs to Reduce Heat Islands | US EPA 
• Plants for Green Roofs—Technical Preservation Services, National Park Service (nps.gov)