Not all energy saving products and techniques are equal. In fact, not all of them are even widely known.
Recently, a study funded by the U.S. Department of Energy and conducted by the Oak Ridge National Laboratory (ORNL) found significant cost savings by creating air space under metal roofing systems.
The study compared the possible energy savings of metal vs. asphalt roofs by doing field testing on an asphalt shingle roof and a stone-coated metal shake roof, both with comparable solar reflectance and thermal emittance levels. The asphalt shingle was directly nailed to the roof deck, with no air space underneath, while the dark-gray metal shake was attached to a batten/counter-batten system that allowed for airflow underneath.
The scientists from ORNL discovered a 45% reduction in heat flow for the metal shake; about 15% of that reduction was attributed to solar reflectance and an additional 30% of the heat flow reduction was due to above-sheathing ventilation.
In cool or cold weather conditions, scientists confirmed that direct-nailed asphalt shingle roofs had significantly larger heat loss than attics with metal shakes and above-sheathing ventilation. The air gap appears to serve as an insulating layer, reducing heat transfer by 50% as compared to asphalt.
The study results have been corroborated by Florida Solar Energy Center and accepted by the ASHRAE SSPC 90.1 subcommittee, indicating that any type metal roof can save a home or building owner up to 25% in annual cooling energy costs compared to a dark-gray asphalt shingle.