The evidence
How much does a cool roof save in Florida?
Florida tests found big savings from white metal and white tile, and small savings from white shingles.
The Florida Solar Energy Center (FSEC) at the University of Central Florida tested several roofs on seven identical homes in Fort Myers. The homes were empty, and the test ran for July 8 to 31, 2000. The control home had a standard dark shingle roof. FSEC then estimated yearly savings for a typical home. Here is what it found.
The attic told the story. FSEC's paper at a national energy conference reported that at the hottest hour of the summer, the attic in the dark shingle home ran 40 degrees Fahrenheit above the outside air. With highly reflective roofs, the attic was no hotter than the outside air. Light shingles and terra cotta tile landed in between.
FSEC estimates of yearly cooling savings by roof type (Fort Myers test, normalized)
| Roof type | Cooling energy saved | Peak demand cut |
|---|
| White metal | About 1,610 kWh a year (23%) | 28% |
|---|
| White S-tile | About 1,380 kWh a year (20%) | 32% |
|---|
| White flat tile | About 1,200 kWh a year (17%) | 34% |
|---|
| White shingles | About 300 kWh a year (4%) | 17% |
|---|
| Terra cotta tile | About 180 kWh a year (3%) | 13% |
|---|
FSEC reported that tile and metal were available with solar reflectances in the 65 to 75 percent range, and that those gave the largest benefit. White shingles reflected much less, so the gain was small.
An earlier FSEC study (1995) painted the roofs white on nine homes that people lived in. Their air conditioning use dropped by 19 percent on average, with a range from 2 percent to 43 percent. FSEC said results depended on ceiling insulation, roof reflectance, where the air ducts ran, and how well the air conditioner was sized for the house.
These are old tests, and the savings figures are estimates for a typical home. Your house will land somewhere in the range. A home with ducts in a hot attic and thin insulation has more to gain.
