Which Green Roof Is Best for Your Facility?
If you’re installing a green roof on a commercial building, you’ve made a wise choice. Green roofs provide economic benefits by reducing energy costs, increasing HVAC efficiency, and extending roof life. Green roofs also enhance neighborhoods by cutting greenhouse gas emissions, improving air quality, and curbing the urban heat-island effect.
The green roof you select for your structure will be one of two basic types. These two types of roofs are called extensive and intensive roofs. Here’s more information to help you choose the best type of green roof for your commercial building.
Goals and Budget Matter With Green Roofs
The extensive green roof may be installed purely for environmental and economic reasons. The extensive type of green roof is not meant to impress, but to function as a heat sink and stormwater control system. Extensive green rooftops often lack walkways, benches, and other infrastructure.
Intensive green roofs, on the other hand, may double as social or recreational spaces for visitors, residents, and staff of buildings. Intensive green roofs used as human spaces will have safe access and other features for human comfort and accommodation. Exotic and diverse plants enhance the intensive rooftop’s allure and attractiveness.
Extensive green roofs are cheaper to install than intensive green roofs because of their limitations. On the other hand, intensive green roofs cost more to install because they require custom irrigation, more labor, and bigger plant lists.
Extensive green roofs are less costly to maintain over the lifetime of the roofs. The low-growing, shallow-rooted plants in an extensive roof installation don’t require pruning or other labor-dependent care.
Intensive green roofs must be monitored to ensure that plants are healthy and secure. Shrubs and trees must be trimmed and tidied in an intensive green-roof setting. Special irrigation, bracing, and feeding systems may be necessary to keep larger trees in good shape.
Weights of Green Roofs Make a Difference
Green roofs are engineered to work within the constraints of a building’s roof supports. Clear-span roofs may be limited in the weight they can hold, while more traditional roofs will need repairs and other adjustments before a green roof can be installed.
If your roof has weight restrictions, an extensive green roof is the best choice. Extensive green roofs weigh between 18 and 22 pounds per square foot.
Intensive green roofs weigh over 22 pounds per square foot. Some intensive roofs weigh over 30 pounds per square foot.
While the weight factor is important, the extra materials on an extensive or intensive roof offer enhanced thermal protection. Certain types of green roofs can insulate buildings from noise pollution as well.
Both extensive and intensive green roofs offer improved insulation to rooftops when combined with standard thermal insulation. Improved insulation from a green roof is best in buildings with high roof-to-wall ratios.
Depth of Growth Media Defines the Type of Roof
An extensive green roof only requires growing media that’s six inches deep or less. Low-growing plants, including ground covers and grasses, make up the majority of the extensive green roof’s vegetation.
Intensive green roofs have growth media depths of more than 6 inches. Plants on an intensive green roof may include perennial flowers, ornamental bushes, and trees.
The various layers below the growth media on an extensive or intensive green roof may include:
- Drainage layer
- Moisture management fabric
- Insulation layer (may be slotted)
- Additional drainage layer (if not slotted)
- Roof-barrier membrane
- Waterproofing membrane
- Roof deck
The precise arrangement of layers is dependent on the type of roof you have and the environmental conditions your building faces.
You can also choose between a modular or built-in-place green roof. The modular roof is built in stages using trays of growth medium and plants. The built-in-place green roof is installed as a continuous feature and is considered more permanent than the modular roof arrangement.
Customization Is the Key to Green Roof Satisfaction
Your green roof installer works with you to design a rooftop that meets your goals. Since each rooftop is different, each green roof will have its own design considerations and challenges. There are no hard and fast rules about the layout and flow of the green rooftop as long as you keep drainage and safety in mind.
Install an extensive green roof that has pathways and benches if you want a low-cost installation that also provides fresh air for your workers. Plant an intensive rooftop with fruit trees and thick shrubs, but keep people away from the rooftop so that birds feel safe to nest in the trees. The options and choices are yours.
Do remember to choose plants that thrive in their designated locations. Install sun-loving trees where they have plenty of rays, and protect shade-loving plants from direct sunlight. Choose plants that are hardy in your growing zone for the best plant success on your green roof.
Take the first step in designing your facility’s new green roof by contacting Berwald Roofing & Sheet Metal today. We use the top products in the industry to install green roofs on commercial buildings throughout Minnesota.