As a roofing contractor in the state of Wisconsin, I continually field requests for energy efficient roofing materials. Most of the requests I receive are 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 consumption. Correct? It seems logical, but it is a common mistake. Energy efficient roof design depends mostly on the outdoor climate and the insulation value of the building on which the roof will be built.
Most types of roofing material are manufactured 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 roofing, 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. In this case, the “Cool Series” brand of shingles are much more expensive.
Significant studies have been conducted to study the effect of roof color on energy consumption. Heat transfer will, in fact, readily occur from the roof into the interior of the building if the building has a poor insulation system 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 significant. 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 building’s energy consumption is to increase insulation levels.
Situations do exist, however, in which the building structure itself cannot be insulated more effectively and a low R-value cannot be avoided. In this situation, roof color will contribute to energy efficiency. So, what color is best in this situation? Answer: It depends on where you live and the exterior climate. Do you have more heating degree-days or cooling degree-days? In Wisconsin, we definitely have more heating degree-days overall. 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 (reflective) roofing material for a building in Southern Florida. Central regions of the United States are considered “color-neutral”. In “color-neutral” 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 facility 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 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 exterior climate zone and existing insulation value. With sufficient insulation, roof color becomes insignificant in the energy efficiency equation. Insulation is the best first step toward energy efficiency and cost effectiveness.
About the Author:
Pro Roofing, LLC is a Licensed and Insured Roofing Contractor Located in Madison, WI. Pro Roofing, LLC has been Wisconsin’s Premier Residential and Commercial Roofer Since 1999.