by Paul Deffenbaugh | 30 April 2010 12:00 am
Two Converging Trends
One of the most significant industry building trends in recent years has been the coming together of government agencies, activist groups and the code community to press for new energy-efficiency standards. In response, standards organizations are producing new code requirements, such as the American Society of Heating, Refrigerating and Air-Conditioning Engineers’ ASHRAE 90.1-2007energy standard.
This version of the ASHRAE standard specifies a full 30 percent increase in required R-values over the 2004 standard. Other examples include the International Energy Conservation Code and state codes, such as California’s Title 24, all of which are calling for increases in energy savings.
Concurrent with this trend-and in some instances predating it-has been another trend: the ongoing development of new structural wall panel systems, which offer varying combinations of benefits and drawbacks.
Some of these systems-such as insulated concrete forms and structural insulated panels-offer energy savings but can require specialized crews and equipment. Others,such as insulated structural metal panels, can pose problems for electrical, plumbing, mechanical and interior finish trades.
But the newest system, Steel Thermal Efficient Panels from Accelerated Building Technologies, Moon Township, Pa., eliminate these drawbacks. S.T.E.P. system panels not only enable building contractors to respond to the emerging-and demanding-new energy performance requirements, they also enable them to achieve unprecedented on-site building efficiency by combining framing, batt insulation and continuous rigid insulation into a single system-which is installed in a single step.
S.T.E.P. Energy Efficiency
The goal of dramatically reducing energy consumption cannot be accomplished by simply adding more insulation to a wall cavity. Although doubling the thickness of insulation in a building envelope would-in theory-double its R-value, each new doubling of insulation thickness would produce only half as much gain as the previous step1.
Even more important, the effective R-value performance of a conventionally installed wall system can be significantly lower than the stated R-value of the insulating material itself due to installation gaps, settling and several other factors we will discuss momentarily.
Because the R-value of insulation alone is a severely limited measure of total building performance, ASHRAE 90.1 2007 and other standards rely on additional, more demanding metrics, such as the maximum assembly U-factor, a measure of total heat transfer through one square foot of wall assembly. Since the U-factor measures heat transfer, a lower number signifies better system performance; this is the opposite of the R-factor, which measures thermal resistance.
In the climate zones that make up the majority of the United States, the latest ASHRAE commercial thermal performance requirements for exterior above-grade walls with steel framing call for an R-13 product plus 7 1/2 inches (191 mm) of continuous insulation,producing a U-factor requirement of 0.064.
S.T.E.P. wall systems not only meet this new standard, they easily exceed it. For example, the accel-E S.T.E.P. system, which first defined the category, provides a product R-value of R-19, with a total wall assembly value of R-17-nearly three times greater than the total wall assembly performance of traditional systems2. The U-factor of 0.051also surpasses the ASHRAE 90.1-2007 standard for most U.S. locations.
Addressing the Causes of Thermal Inefficiency
Steel thermal efficient panels, such as the accel-E S.T.E.P. system, fuse cold-formed steel framing members and expanded polystyrene insulation into a single system, which generally is manufactured in 4-foot (1-m)panels with steel studs at 24 inches
(610 m) on center. Thermal slots in the stud optimize structural and thermal performance, and the panels themselves lock together to minimize air intrusion and eliminate insulation gaps.
Framing Factor
More than 25 percent of a traditional wall system may be composed of non-insulated framing members, which continue to transfer heat and cold by means of thermal conduction. In S.T.E.P. wall systems, the framing members are embedded within continuous foam insulation. Moreover,the inner and outer framing members are separated. This design eliminates the thermal bridging effect of traditional technologies.
Air Infiltration
Unwanted air infiltration can account for up to 30 percent of heating and cooling costs. A S.T.E.P. panel’s rigid continuous EPS insulation, coupled with tight, tongue-and-groove joints between panels, effectively seal off air infiltration.
Moisture
The closed cell, non-porous EPS insulation of the S.T.E.P. panel prevents air movement inside the wall cavity, there by reducing the opportunity for moisture formation through diffusion,convection or condensation. Moreover, if the EPS insulation somehow does get wet,it will dry with no degradation to the material, and no loss in energy performance.
Traditional Building System Strengths
The accel-E S.T.E.P. wall system features precut window and door openings, with an open cavity that simplify the installation of electrical, plumbing and mechanical systems. The system’s thermal performance also eliminates the need for a separate continuous insulation, thus making it easier to fasten any cladding while providing a stronger, more even surface.
Above all, by combining framing, batt insulation and continuous insulation into a single process, S.T.E.P. panels can reduce labor costs by up to 50 percent over conventional stick framing. Similarly, the construction cycle for wall construction can be reduced by a much as 66 percent over other systems, according to RS Means Construction Cost Data.
In many applications, the entire building envelope can be completed in a matter of days, with no on-site cutting, drilling or welding required. Since a 4- by 8-foot (1-by 2-m) S.T.E.P. panel weighs less than 50 pounds (23 kg), cranes and other specialized equipment generally are not needed for panels up to 30 to 40 feet (9 to 12 m).
Furthermore, because all components are factory fabricated to precise requirements, the amount of on-site waste is reduced dramatically. In addition, S.T.E.P. systems’ steel framing members are made of recycled steel, and are themselves recyclable. As a result, a S.T.E.P. wall system can contribute points to as many as four LEED categories.
Jeff Peskowitz is director of distribution sales & marketing for Accelerated Building Technologies, Moon Township, Pa.
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