Cool Roofing Options/Regulations

There are two primary types of widely accepted cool roofing products on the market today – (1) protective paints and coatings; and (2) single-ply roofing systems. Related, but different, categories that contribute to energy efficiency include garden roof systems (GRS), sometimes called “green” roofs, and solar-integrated roofs.

Reflective paints and coatings can be an effective short-term solution for reducing energy costs, and can make any roof “cool” temporarily, but most facility owners looking for long-term, low-maintenance solutions opt for a complete single-ply roofing system.

Single-Ply Cool Roofing Systems:

Polyvinyl chloride (PVC) single-ply roofing systems have the longest track record of long-term performance among white single-ply cool roofing systems. The first white PVC systems were installed in Germany during the early 1960s, but it was overall performance and life-cycle cost benefits that made these early systems popular in Europe during the 1970s and ’80s. Introduced to the United States in the 1970s, in 1985 PVC roofing systems were the first single-ply roofing products to obtain a standard designation from the American Society for Testing and Materials (now ASTM International): ASTM D4434 – Standard Specification for Poly(vinyl chloride) Sheet Roofing.

More recent cool roofing single-ply developments include the introduction of co-polymer alloys (CPAs) during the 1980s and thermoplastic polyolefins (TPOs) in the 1990s. An ASTM International standard for TPO single-ply roofing was established in 2003.

Today, many single-ply roofing systems are available in white or light colors, including ethylene propylene diene terpolymer (EPDM) and modified bitumen with a white granular cap sheet. PVC and TPO thermoplastic single-ply systems are the most popular and best-performing in terms of long-term reflectance. The coolest among these systems typically range from 70 percent to 88 percent solar reflectance.

Garden roof systems go back as far as the Hanging Gardens of Babylon, but they are enjoying renewed interest primarily as a means of reducing the effects of UHIs while creating aesthetically appealing, environmentally friendly construction.

ASTM International standard, studies indicate that rooftop gardens moderate and lower the temperature fluctuations of the underlying roof membrane (usually a complete single-ply system), reduce indoor air temperatures in the spring and summer, and also delay and reduce water runoff. They may also extend service life since they shield the underlying roof membranes from ultraviolet radiation, hail, wind and foot traffic.

Intensive GRS systems have soil up to one foot deep, capable of maintaining trees and bushes. Widely publicized for their aesthetic appeal, intensive GRS systems require substantial roof deck structures to handle the additional weight. These roofs are relatively costly to build and maintain, but reduce rainwater runoff by up to 50 percent.

Extensive green roof systems are lighter, using just three to four inches of soil. Because they are lighter than intensive GRS systems, roof decks with less load-bearing capacity can support extensive roof gardens, making them more cost-efficient.

Solar-Integrated Roofing is a very recent development with a great deal of potential, especially when combined with a reflective cool roofing system. Photovoltaic cells convert sunlight into electricity without creating pollution or consuming energy. As the name implies, solar-integrated roofing is intended to generate power for the building it protects, and possibly return excess electricity to the local power utility for additional savings. Much more expensive to install, these roofing systems may prove to have the best life-cycle cost profile, provided they also prove to be reliable and long-lasting. These systems are so new that no testing has been completed to determine:
• Potential loss of reflectivity due to solar cells replacing reflective surface area
• Effects on indoor temperatures, with or without air conditioning
• Impact on power demand by HVAC systems
• Impact on mitigation of UHIs and air pollution, if any

The energy conservation and environmental benefits of cool roofing have resulted in many federal, state, and local government initiatives designed to encourage or mandate the use of reflective roofing materials and systems. The ENERGY STAR Roof Products Program led by the EPA is perhaps the most visible program, but there are several others.

In 1999, Executive Order 13123 was issued to provide guidance in roof selection for federal buildings. Now known as Federal Acquisition Regulation Case 1999-011, this regulation mandated that federal office buildings reduce energy usage 30 percent by 2005, with a further 35 percent reduction by 2010. It also required federal industrial buildings and laboratories to reduce energy consumption 20 percent by 2005, and another 25 percent by 2010. Federal agencies also must use ENERGY STAR products when available, and decisions must be based on energy and life cycle cost analyses.

In April of 2005, President Bush signed legislation offering tax deductions to owners of private commercial buildings that exceed the ASHRAE Standard 90.1.

All but a handful of the 50 states have established regulations and/or incentives to encourage cool roofing or energy efficiency in buildings. For instance, the Georgia White Roofing Amendment requires the use of additional insulation for roofing systems that do not have reflectance and emittance of 75 percent or higher.

An incentive-based rebate system was so successful in California that the legislature adopted mandatory cool roofing standards as part of Title 24, a wide-ranging “green” construction bill that became effective in October, 2005. Title 24 specifies that new and replacement commercial roofs – any low-slope roofing project that requires a construction permit – must have a minimum initial thermal emittance of 75 percent, and a minimum initial solar reflectance of 70 percent, as rated by the Cool Roof Rating Council.

In 2003, the Chicago Energy Code mandated that all new low-slope roofs have a minimum initial and weathered reflectance of 25 percent. After December 31, 2008, low slope roofs must meet or exceed ENERGY STAR criteria.

In cooperation with state and local governments, many utility companies offer rebates for using reflective roofing systems. These rebate programs are offered nationwide, not just in southern climates. For instance, Xcel Power, the fourth largest utility company in the U.S., has awarded rebates as far north as Minnesota.

For more information on Cool Roofing, visit www.duro-last.com