Energy Efficiency And Roof Design
As a roofing contractor in the state of Wisconsin, I continually field requests for light colored (reflective) roofing for the purpose of energy efficiency. A white or light colored roof will reflect sunlight, keep the building cooler, and reduce energy consumptionCorrect?
It depends on where you live and the insulation value of the building.
Most roofing material comes in a variety of colors. EPDM (rubber) membrane, for instance, is a very common low slope roofing material that comes in black or white. In the case of EPDM, the white color is much more expensive. Many consumers will justify spending more on white instead of black EPDM since they believe that there will be energy savings. Asphalt shingles come in a variety of different colors from light to dark. Some shingle manufacturers, such as GAF, have marketed Cool Series asphalt shingles that are designed to be more reflective of sunlight.
Significant studies have been conducted to study the effect of roof color on energy consumption. Heat transfer will occur from the roof into the interior of the building if there is a low level of insulation and resulting low R-Value (thermal resistance). As R-value and thermal resistance increases with better insulation systems, the type and color of roofing material becomes less and less important. In general, an R-value of 30 or more negates any energy efficiency gains from white or light colored roofing material in hot climates. It stands to reason the most effective way to decrease a buildings energy consumption is to increase insulation levels.
There are situations in which the building structure itself cannot be insulated more effectively and a low R-value cannot be avoided. What color of roofing material would be best in this situation? It depends on where you live and the climate. Do you have more heating degree days or cooling degree days? Here in Wisconsin, we definitely have more heating degree days. Therefore, a dark colored roof will help heat interior building spaces and decrease energy consumption over time. In colder climates, dark colored roofs are the most energy efficient. The opposite is true for hot climates. It would be well worth the extra investment in purchasing white roofing material in Southern Florida. Central regions of the United States are considered color-neutral. In these areas, studies have shown that energy efficiency is not impacted by roof color.
With the increase in roofing material choices, it has become increasingly important that roof designers, contractors, and facilities managers consider the right roofing material for the right situation. Reflective roofing has become a knee-jerk reaction for some designers and contractors who do not take climate zones or insulation levels into consideration. Focus should remain on insulation systems and improving insulation value when optimizing energy efficiency. Advances in insulation technology have created opportunities to increase insulation value in almost any circumstance. Spray-on foam insulation and plywood manufactured with imbedded rigid foam insulation have become popular and effective systems to increase R-value in tight spaces.
Every building and every roof system is different. Roof design for energy efficiency must take into consideration climate zone and insulation value. With sufficient insulation, roof color becomes insignificant in the energy efficiency equation.