Black – or white? Dark roofs vs. cool roofs irrelevant for an energy-efficient roofing solution BY TERRY O’CONNOR, CANADIAN BUSINESS MANAGER, FIRESTONE BUILDING PRODUCTS
Light-coloured roofing systems that deliver high solar reflectance and high thermal emittance are categorized today as “cool roofs.” The growth in highly reflective roof systems in the last decade has been principally driven by EnergyStar, the Cool Roof Rating Council, U.S. and Canadian building councils and LEED® requirements. However, the misconception that reflective roofing is optimal for a building’s energy savings – regardless of the geographical position – can be costly. Reflective roof systems have grown consistently and rapidly in temperate areas, like the southern U.S., where overall building energy consumption is driven predominantly by air conditioning costs. In Canada, the growth in white roofs can be attributed to other reasons, including: 1. A mechanically-attached white roof may be the more cost-effective roof solution; 2. Specifications for U.S. owners that are simply transferred to Canadian operations;
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Ops Talk Fall 2009
Roof contractors laying out a cost-effective Firestone RubbersGard R.M.A EPDM System.
3. The need for LEED® points; and 4. The perception that white roofs are environmentally-friendly everywhere. Despite the perception that white reflective roofs are the most energy-efficient roofing solution, numerous professional studies have proven this to be incorrect. In cooler, northern climates, the energy required to heat a building is often a more significant factor in overall
energy usage. For example, Table 7.4 of the 2007 Buildings Energy Data Book, published by The Building Technologies Program within the U.S. Department of Energy’s (DOE) Office of Energy Efficiency and Renewable Energy, outlines energy use intensity in various commercial building types, comparing heating and cooling as a percentage of total energy consumed. The average results show that heating accounts for 29 per cent of the energy consumed within a building nationally, while cooling totals a mere six per cent. For educational facilities, the heating-to-cooling ratio is 33 per cent to five per cent, respectively. In Canada, where Heating Degree Days (HDD) largely outnumber Cooling Degree Days (CDD), black membranes like EPDM continue to outperform their light-coloured counterparts for energy efficiency. Dark-coloured roof membranes absorb solar radiation and transfer it into the building, where it heats the interior and places less demand on the heating system. This is especially beneficial in educational facilities that are usually closed during the peak cooling sea-
