green roofs
ENGINEERING CONSIDERATIONS
When designing a green roof system it is important to consider the specific project’s requirements such as its function, location, the structure itself, roof accessibility, installation, and maintenance. Therefore, it is a process that involves coordination between the structural engineer, owner, architect, landscape architect, and the M&E. Some structural considerations when designing a green roof include:
Additional loads of green roof
Wind pressure:
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In reference to ASCE7-05, Chapter 6: Wind Loads, wind pressure is related to geographic location and terrain, and the building’s shape, size, and features. The green roof system must prove to be stable under the specific wind pressure of the building. |
Uplift:
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A pressure differential can be created when wind is redirected and accelerates, which can then in turn cause an uplift force on the rooftop. There is minimal information regarding uplift of specific green roofs, so green roofs are often treated as if they are pavers of similar mass, and special attention is given to negative wind pressure. |
| | When taking a large uplift force into account, it may be necessary to include additional applications such as: limiting the green roof to the center of the rooftop while using heavier ballast along the perimeter, overlaying the green roof with netting, or fully adhering the green roof.
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Parapet design:
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This relates to the positive and negative wind forces and depends on the building’s size and height. Depending on the parapet shape and design, it may help to moderate and reduce uplift pressures, especially for taller buildings.
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Roof slope:
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This depends on the friction present and the force exerted against the parapet. Buttresses may be necessary for long roofs and roofs with great slopes to distribute the load from the parapet. The North America’s Green Roofs for Healthy Cities determined that the maximum slope for a green roof should be 40 degrees based on containment challenges and soil moisture.
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The following website provides more detailed engineering considerations:
http://www.liveroof.com/architecture.php
