Almost the same as the direction the roof faces. 1.44 degrees for direction. 1.45 degree increase from white to black.
The following conclusions are based on data from our numerical model:
- The greatest influence on roof temperature is geographic location. The mean roof temperatures for Miami and Green Bay, Wis., for example, differ by 18 degrees Celsius.
- The direction a roof faces has the second greatest influence on average roof temperature (in excess of 1.44 degrees Celsius in the east through south-to-west range studied, but the real difference is greater because other directions, such as north, will be cooler).
- The color of roofing materials influences the mean temperature of a roof system slightly less than direction (1.45 degrees Celsius average for these parameters).
- Ventilating the area under a roof deck reduces the average temperature 0.5 degrees Celsius (about one-third the influence of the direction or color and one-thirty-sixth the influence of geographic location). Even with wind assistance, ventilation reduces average roof temperature about half as much as using white rather than black shingles.
- Within the ranges studied, slope has the least influence on average shingle temperature.
Many shingle manufacturers provide warranted products that are widely distributed and are of many colors and exclude from warranties those shingles installed on unventilated decks. This exclusion has no justification; the variations in geography, direction and shingle color have greater influences on average temperature than the degree of ventilation.
However, ventilation should be recommended to remove the small quantity of moisture in a roof system; it can prolong the life of a wood deck even if it does not extend the life of shingles.