Sustainability Series: Green Roofs

With increased urbanization, green roofs are becoming a major trend. They offer many advantages to building owners and occupiers, the general public, and the environment: better insulation, reduced power consumption, stormwater retention, improved air quality, and a biodiverse environment offering aesthetic diversity. However, green roofs may introduce property considerations and concerns that owners and occupiers should be aware of when reviewing their property and business risks.

Green roofs comprise specific vegetation designed and installed on a series of components, including moisture retention material, a drainage system, a root barrier, and a protective layer for both the insulation and underlying roof surface.

Property Risk Considerations

Let's take a closer look at a few features that will likely be of interest to commercial property insurers when evaluating the building's overall risk profile.

1. Potential for water leakage damage

The irrigation pipework may be susceptible to freezing. Leaks in waterproofing membranes due to root growth or temperature fluctuations may expose the underlying roof structure to damage or corrosion. Drainage systems may become blocked by soil and vegetation. These risks are particularly relevant in the construction phase.

Loss Prevention Tips: Penetrations in the roof should be minimized. It is important to include leak detection systems below the waterproofing membrane. Size gutters to accommodate both rainfall and irrigation runoff and maintain them regularly, with specific inspection points included. Consider the impact of roof gradient on the density of growth media and its propensity to shift or slide during heavy rain events.

2. Fire load

Green roofs and their supporting components (e.g., vegetation and waterproofing membrane) typically add combustible loading to a roof and increase the potential for ignition from exposing fires or other ignition sources. In some cases, the design of a green roof may encompass space for recreational activities, introducing ignition sources such as lighting, electrical installations, barbecues/grills, and smoking.

Loss Prevention Tips: Limit the overall fire risk by maintaining adequate moisture content of vegetation, regular removal of dead vegetation, and careful design and placement of noncombustible fire breaks. Include manual firefighting equipment such as fire hydrants, fire hose reels, and portable fire extinguishers, along with access provisions for the fire brigade. Potential ignition from electrical equipment, smoking, or other sources should be identified and carefully managed.

3. Susceptibility to collapse

Green roofs introduce live loads associated with landscaping, precipitation, induced saturation due to irrigation, and periodic replacement of new soil and growth of vegetation.

Loss Prevention Tips: The load carrying ability of concrete roofs versus all other types (e.g., long span steel) should be considered over the roof lifecycle. Some roofs may be susceptible to deformation over time, affecting the operational efficiency of certain components that originally functioned properly. Future changes may affect the structural integrity and should undergo formal review. Concrete roofs are generally more resilient than other roofs to changes that increase live loading.

4. Damage from natural hazards

Green roofs are susceptible to natural hazard perils such as seismic forces and wind uplift pressures. Vegetation or potentially the entire roof system may be damaged, requiring replacement.

Loss Prevention Tip: The system, including any moisture/root barriers, should be properly secured to structural elements (growth media should not be relied upon). Green roofs should not generally be installed in areas with elevated wind exposures such as coastal areas subject to hurricanes.

Green Roofs provide many environmental benefits, especially in urban locations where vegetation may be scarce. However, if a green roof is to be installed, ensure that the considerations outlined above are incorporated in the design, installation, and future maintenance requirements to mitigate the potential for loss.

For more questions, contact Risk Engineering and download our Green Roofs guide.

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