The media relations group for Oak Ridge National Laboratory just released more information about recent field tests by ORNL of a new roof and attic system that keeps homes cool in the summer and prevents heat loss in the winter. The system is explained in the graphic embedded above (click to expand). In addition, I’ve included some graphics below to illustrate more of what the system looks like and how it saves energy.
The system employs a passive ventilation strategy that is expected to cost about $2,000 for a retrofit situation with savings of roughly $100 per year, yielding a payback of about 20 years.
Foil covered polystyrene insulation (with the ventilation gap) is installed over and between rafters for new construction or on top of an existing shingle system in a retrofit. With the new roof assembly, air moves from the underbelly of the attic into an inclined air space above the roof, according to an ORNL statement, so that “heat that would have gone into the house is carried up and out,” said Bill Miller of ORNL’s Building Envelope Group.
In the summer, the temperature of the attic is reduced as a result of the roof detailing and, according to observations by ORNL, the thermal load of the home is thereby reduced. Further, ORNL found improved efficiencies even if the attic floor is insufficiently insulated.
The research and findings are discussed in more detail in a paper, “Prototype Roof Deck Designed to Self-Regulate Deck Temperature and Reduce Heat Transfer,” published by the National Roofing Contractors Association. A PowerPoint of the background research can be found here [PDF].