Where do you stand on vegetative roofs?

By Cyrus C. Butts, CBO, LEED, AP November 17, 2015

New green products and technologies are constantly becoming available to homeowners and businesses. One of the more intriguing innovations for city dwellers is vegetative roofs. They’re eco-friendly and appropriate for large and small properties, either residential or commercial. Quite simply, they’re building roofs covered in vegetation. They have a beneficial impact on storm runoff, air quality, and energy savings. And they look kind of cool.

Vegetative roofs clearly have their benefits:

  • Energy savings: Plant systems act as insulating barriers, reducing the fluctuation in a building’s temperature. That decreases the amount an owner spends annually on heating and cooling systems, and it reduces the stress on a building’s HVAC system.
  • Air quality: A healthy green roof increases the amount of oxygen in the air and reduces airborne impurities.
  • Storm water management: Green roofs retain water and release it slowly, which is particularly valuable during large storms that can produce water runoff leading to localized flooding.

Property owners also need to consider the disadvantages:

  • High maintenance costs: Maintaining a vegetative roof can require significantly more upkeep then a traditional roof. You have to perform periodic landscaping, weed removal, and removal of dry (flammable) debris.
  • Unwanted wildlife and insects: Any plant system provides a home for birds, insects, and other wildlife, which is often unwanted.
  • Lack of access: Vegetative roofs cover the membrane of a roof system and prevent visual inspection of a roof’s condition, and that may lead to uncorrected leaks.

In addition, firefighters and insurers have their own concerns. For fire departments, vegetation makes it more difficult to vent a fire, a common tactic with some structural fires where firefighters literally chop a hole through the roof. The vegetation can mask the condition of a roof under stress. Finally, the plantings and any related gardening equipment can make it more difficult for firefighters to maneuver on the roof.

Insurers share firefighters’ concerns because those disadvantages can put occupants and the property at risk. Also, the extra weight of a green roof can range from 35 to as much as 150 pounds per square foot, adding stress to a structure and its roofing. There may be supplies, furnishings, and other equipment on a green roof that can become projectiles in a windstorm or hurricane.

What do you think? Take our one-question survey, and let us know.

For more information on structural fire protection and building code enforcement, go to our ISO Community Hazard Mitigation website. You’ll find details on our Public Protection Classification (PPC™) and Building Code Effectiveness Grading Schedule (BCEGS®) programs.


Cyrus C. Butts

BCEGS Field Analyst, ISO Community Hazard Mitigation