Energy Efficiency and the Impact on the Atmosphere
Many of the rating systems encourage the construction industry to achieve increasing levels of energy performance above the prerequisite standard to reduce environmental impacts associated with excessive energy use. There are several ways the design team can help a building lower its energy consumption, allowing it to become less harmful to the environment (e.g. reduced air pollution, less contribution to global warming) and more economical for the owner (e.g. decreased operational costs). When considering products and systems that can positively affect the building’s energy load, it is important to consider a whole building approach and think holistically. As with other aspects of sustainable design, plastics can play a role when employed as insulation materials.
The use of polyisocyanurate (polyiso) insulation materials can directly contribute to strategies conserving energy and mitigating the effects of global warming, while also reducing dependence on foreign energy sources. Polyiso insulation used for roofing is very thermally efficient, as determined by using long-term thermal resistance (LTTR) values (i.e. a 15-year time-weighted R-value).
Polyiso manufacturers produce rigid foam board with third-generation, zero ozone-depleting blowing agents. All polyiso insulation products are chlorofluorocarbon (CFC)-free and have no global warming potential blowing agents.1 These qualities are critical as the impact of climate change is being studied as a worldwide environmental concern. The thermal efficiency of polyiso, due to its high R-value per inch, facilitates compliance with American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1-1999, Energy-efficient Design of New Buildings Except Low-Rise Residential Buildings, and many local energy codes.2
Expanded polystyrene (EPS) does not experience thermal drift, meaning its R-value remains constant throughout the life of the building. Whether in a sheathing, roofing or below-grade application, EPS can provide compliance with ASHRAE 90.1-1999. Additionally, this material’s use in insulating concrete forms (ICFs) and structural insulated panels (SIPs) can also contribute to this category with increased energy efficiency. Their tight construction enables designers to specify smaller HVAC units, which can contribute to reduced energy needs and costs. The air-tightness of expanded polystyrene also moderates internal temperature swings, which can increase comfort levels for occupants.
Extruded polystyrene (XPS) can help achieve high energy efficiencies by providing stable, long-term insulation value, as well as blocking thermal shorts that may occur in roof, wall, and below-grade assemblies.
Spray polyurethane foam
Building owners have used spray polyurethane foam (SPF) as a roofing, insulation, and sealing product for many years. For example, Texas A&M University has documented energy savings from the use of SPF roofing systems by calculating the energy use of their buildings before and after the application of those roofing systems. According to their studies of more than 743,224 m2 (8 million sf) of roofing, energy savings paid for the cost of the SPF applications in three to four years.3
The dark-colored membranes of black-surfaced roofs absorb radiant heat, raising the roof’s surface temperature. Thermal bridges such as fasteners and gaps in insulation boards transport the heat within the building, leading to the possibility of increased HVAC cooling needs.
SPF roofing systems are applied above the roof deck and eliminate thermal bridging by providing a continuous layer of insulation over existing thermal bridges in the roof deck and/or assembly. The plastic can have a high aged R-value of between six to seven per inch. Additionally, these SPF roofing systems are typically coated with light-colored, reflective coatings, which can further help reduce this urban ‘heat island’ effect.
As an efficient insulating material for heat and cold, vinyl allows windows and doors to maintain an even temperature, keeping them comfortable to the touch and decreasing condensation caused by indoor/outdoor temperature and humidity differentials. The design of vinyl window frames further enhances their energy efficiency by creating chambers in the frame that provide additional resistance to heat transfer and insulating air pockets. The frames and sash corners are fusion-welded for maximum strength and protection against air and water infiltration.
Many vinyl roofing membranes have also been recognized by the Energy Star® Roof Products Program of the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Energy (DoE). The energy savings realized by installing a vinyl membrane roof on the Donald Bren Hall at the University of California, Santa Barbara helped that building earn prestigious Platinum status under the U.S. Green Building Council’s (USGBC’s) Leadership in Energy and Environmental Design® (LEED®) rating program.
The light color of vinyl membrane roofing materials has also been shown to have a positive impact on air quality. Researchers at the National Aeronautics and Space Administration (NASA) found summertime urban air temperatures can be greatly reduced by using light roof surfaces instead of dark-colored industrial/commercial materials. Decreases in urban air temperature may help improve air quality, since smog is the result of photochemical reactions triggered by air temperature increases. When installed on multiple buildings in an urban setting, light-colored vinyl membrane roofing can help diffuse heat within a city and assist in lowering air-conditioning demands, thereby helping to lessen smog formation.
1 For more information, see “A Blowing Agent Update,” by Lorraine Ross in the February 2005 issue of Professional Roofing.
2 As insulation formulation may vary from manufacturer to manufacturer, design professionals should consult the suppliers’ specification sheets to understand the exact properties, including the actual R-values. Factors affecting the R-value include thickness of application (i.e. the thicker the foam, the better the aged R-value), the substrate, and the covering systems used (i.e. the lower the perm-rated covering and substrate, the higher the aged R-value).
3 This information comes from a Spray Foam ’94 presentation by Sam Cohen, PE, entitled “Texas A&M’s SPF Roofing Experience.”