Condo Media - January 2010 - 24

MAINE N e w s by Jack Carr, P.E., LEED-AP R e g i o n a l Cool Roof A New Green Technology o, this is not the name of a new Maine rap band, rather “Cool Roof” is a term being used to describe the hot, new green technology for flat (low slope) roof design. Condominium board members and property managers of urban midand high-rise buildings often face flat roof maintenance issues, and now a new wrinkle in the roofing decision process has arisen: black or white. In the recent past, most flat roofs were made with a rubber-like elastomeric membrane called EPDM. Though black EPDM still accounts for the majority of flat membrane roofs for condo, commercial and industrial buildings in the northern states, things are changing. Cool roofs are designed to reduce energy consumption as well as what is commonly called the urban heat island effect. Cool roofs are categorized into three basic types: white, reflective-coated or green (vegetated) roofs. White roofs are the most common, with TPO (thermoplastic polyolefin) and PVC (polyvinyl chloride) being the typical choices. PVC and TPO roofs have the same wear and cost factors. However, PVC materials have some negative characteristics, such as high toxicity and unrecyclability. So, for ease of comparing black to white we will consider EPDM vs. TPO in our comparison discussions. TPO roof membranes have longer lives, on average lasting 25 years compared to EPDM lasting 20 years. This is partially due to TPO’s resistance to UV and thermal expansion damage. Some TPO products developed bad reputations due to their inability to handle severe cold, which in some cases caused the membrane to shatter. These problems are reported to have been fixed with today’s TPO roofing materials. C A I N The initial cost favors EPDM roofs. However, when lifecycle and energy cost issues are considered, the black and white roofs become competitive. Installation methods differ in that EPDM seams are taped or adhesively sealed while TPO seams are welded by a thermal process. There are strong forces pushing the general acceptance of white roofs. States, such as California, passed laws in 2005 requiring the use of reflective roofing materials. And, individual cities, such as Chicago, have established building codes to favor its use. There is evidence developing that shows the heat island’s effect of black surfaces, including not just roofs but also parking lots, paved roads and building facades, can impact local weather characteristics. Energy Efficient The nation’s largest green building advocates also are influencing architects and building owners by favorably rating buildings with cool roofs. Under the joint program of the U.S. Environmental Protection Agency (EPA) and Department of Energy (DOE), to receive an Energy Star label under its Roof Product Program, it must have a solar reflectivity of at least .65 and weathered reflectance of at least .50, according to EPA testing procedures. The Cool Roof Rating Council (CRRC) created a rating system for measuring the solar reflectance and thermal emittance of 850 roofing products. The Green Building Initiative has instituted its Green Globe system in the United States and Canada to develop benchmark criteria for a building’s likely energy consumption as a result of roofing material’s solar reflectance and thermal emittance. The U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) rating system is now widely used for most publicly funded building projects and many high-profile, non-government buildings. Architects seeking a LEED certification for their project will receive credit for white, cool roofing meeting LEED solar reflective index guidelines. So with all of this horsepower pushing for cool roofs, it seems like an easy black or white decision for the condo board facing a roof replacement project. Maybe not. For northern condos the problem is a little complicated. CRRC admits to a “winter penalty” when cool roofs are installed in northern climates. DOE building modeling data reveals that, in the north, heating is a much more significant factor in energy use than cooling. In fact, heating accounts for 29 percent of energy used compared to only 6 percent for cooling. Insulation is a more important element for energy efficiency than cool roofs here in New England. It has to do with the amount of heating degree days (HDD) and cooling degree days (CDD). For example, Boston has 5,841 HDD and 646 CDD as compared to Albuquerque’s 4,361 HDD and 1,211 CDD. Therefore, using DOE’s cool roof calculator, Boston’s high number of HDD’s and positive winter heat gain results in lower energy usage and fewer carbon emissions with an EPDM roof. So, talk with your roof consultant and remain cool. CM Jack Carr, P.E., LEED-AP, is general manager of Criterium-Mooney Engineering in Portland, Maine, and is a member of the Condo Media board. He is a frequent author and speaker. CONDO MEDIA • JANUARY 2010

Condo Media - January 2010

Table of Contents for the Digital Edition of Condo Media - January 2010