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Part 3: Daylighting, Energy Production Are Among Energy Possibilities Of Resilient Roofs
August 2014 -
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After a severe weather event when the power is out and lights are not working, rooftop daylighting systems can provide light for occupants. Daylighting devices on rooftops are "engineered skylights" that are sized, located, and appropriately reflective to provide enough light for occupants to function reasonably well. Some have PV-powered rotating reflective surfaces to provide as much light as possible when the sun is out, and no grid-based electricity is needed. It's important to note that any opening in a rooftop will decrease, to some extent, the overall R-value of the roof system. Owners should consider the trade off between daylighting and the loss of R-value, as well as the impact resistance of the daylighting components.
For longer-term building resiliency, energy production (from photovoltaic or wind power systems) can be included on a rooftop. Rooftop photovoltaic (also known as distributed generation) may not be able to provide electricity to operate an entire building, but rooftop energy production can operate key components of a building during a power failure. It's important to realize that grid-tied PV systems need battery back up (i.e., storage capacity) in order to provide electricity during a black out. A grid-tied PV system without storage capacity needs a functioning electrical grid in order to provide power. Consider the cost to a grocery store when loss of power means throwing away aisles of refrigerated and frozen food. A battery-backup PV system might well be worth the cost. Also, high winds can damage rooftop PV, and there is anecdotal evidence that ballasted-only PV systems may not stay in place during a high-wind event. A few, appropriately placed mechanical attachment points (e.g., at corners and perimeters) can provide significant resistance to high winds, ensuring long-term use of a rooftop PV system. It's cheap insurance and provides peace-of-mind.
Resiliency of roof systems is a focused subset of the overarching idea of durability and long-term performance. Drainage, traffic protection, wind and fire resistance, moisture management (e.g., vapor and air barriers), maintenance, and quality installation are just a few of the components and ideas that lead to long-term performance of roof systems.
Part 1: Go Beyond Minimum Requirements To Keep A Roof Resilent
Part 2: Resilient Roof Systems Can Be Designed To Handle Higher Wind Speeds Than Codes Require