Black – or white? Dark Roofs vs. Cool Roofs

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 Energy Star, the Cool Roof Rating Council, U.S. and Canadian building councils and LEED® requirements. How ever, 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;

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 in correct. 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 Effi ciency 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-

sons, when reflective membranes perform best.

The colour of the membrane, however, plays a miniscule role when it comes to energy efficiency on a building insulated with at least two layers of staggered polyiso insulation. The numberone way to reduce greenhouse gas emissions is to increase the levels of insulation; this offers the greatest return on investment, regardless of the building’s physical location.

“COOL” BALLASTED EPDM ROOFS

When seeking cool roofing options, many building professionals do not realize that EPDM provides similar energy savings as its white counterparts. An extensive analysis of roofing system energy performance by the Single Ply Roofing Industry and Oak Ridge National Laboratory indicated ballasted and paver EPDM roofing systems can save as much energy as a reflective or cool roof in southern climates.

In the study, ballasted EPDM profiles delayed the temperature rise for up to three hours, effectively moving about 20 per cent of the cooling load into off-peak hours when energy costs are lowest. As such, the California Energy Commission (CEC) and the American Society of Heating, Refrigeration and Air-Con -

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(Langley by appointment only) First Nations University of Canada – the Saskatchewan Indian Federated College with a 45,000 sq. ft. Ballasted EPDM. dition ing Engineers (ASHRAE) have updated their cool roofing standards to recognize ballasted roof systems as an acceptable alternative.

Also, even though it has fewer HDDs than Toronto, Montreal, Calgary and most other Canadian cities, the City of Chicago added ballasted EPDM as a cool roof alternative in its municipal code earlier this year, as well. So, it is increasingly apparent that although reflective roofing materials have inherent value in the fight to gain energy efficiencies, the issue is not simply black versus white.

Energy-efficient roofing system de sign is ideally comprised of a quality vapour barrier, two layers of staggered insulation, and an optional high Rvalue coverboard where there is appreciable traffic on the roof.

The solution of choice above this may be any fully-adhered system, such as a multi-ply asphalt, 2-ply SBS Modified Bitumen or single-ply EPDM, TPO or PVC. If and when white roofs are mandated for a building, use of a properly designed insulation assembly will mitigate the overall energy consumption through the roof system, making the roof membrane colour irrelevant. ❏

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