The key to designing energy-efficient buildings can be found in your home’s kitchen. The next time you are thirsty for a cold drink or want to grab a leftover piece of pizza, open the refrigerator and consider what makes it effective.
With relatively little energy, the appliance maintains a consistent internal temperature well below that of the surrounding room. It’s no secret that proper insulation and sealing are critical to keeping warm air out and reducing the compressor’s operating time. In many buildings, by comparison, large amounts of heat are regularly lost or gained through air leakage or thermal bridging commonly found in traditional construction methods.
The same basic design approach used for refrigerators and freezers readily exists for buildings. Structural insulated panels (SIPs) are similar to a fridge’s top and sides in providing monolithic construction that integrates the insulation and structural elements and minimizes gaps needing seals. SIPs create a tight envelope, which reduces air leakage, plus they minimize thermal bridging more effectively than other building methods, including stick framing.
The following is a discussion of the energy-efficiency research conducted on SIP buildings, other “green” attributes of SIPs construction, and the range of structural applications in which design professionals can use the panels.
SIP construction is approximately 15 times more airtight than stick framing, according to research conducted at U.S. Department of Energy’s Oak Ridge National Laboratory (ORNL). The lab’s blower-door tests showed that a SIP room had a leakage rate of 8 cubic feet per minute at 50 pascals, compared to the 121 cubic feet per minute at 50 pascals of conventional wood framing.
Heat-flow resistance is significantly greater also (approximately 47 percent), with SIPs instead of stick construction for walls of comparable thickness. ORNL evaluated the overall thermal performance of wall assemblies constructed using the two building methods. Its tests took into account heat transfer through the structural members, at corners and other joints, and around windows to obtain a “whole wall” R-value. The results are shown in Table 1.
The SIPs outperformed both conventional stick framing using 2-inch-by-4-inch studs at 16 inches on center, as well as “advanced framing” using 2-inch-by-6-inch studs at 24 inches on center. To further boost energy performance, designers can specify thicker SIP panels with even higher R-values, as shown in Table 2.
SIPs work well in both hot and cold climates, helping reduce heating and cooling energy demands by up to 60 percent. Recent project examples in wide-ranging climate conditions include a large multi-family apartment complex and grade school in Las Vegas, high-altitude camp buildings in the Peninsular Range east of San Diego, and homes and government buildings in Alaska. The design teams for each of these projects chose SIPs because of their superior insulating capabilities and ability to meet structural requirements.
In addition to energy efficiency, SIPs provide other green building benefits and can help contribute up to 39 points in LEED for New Construction and up to 46 points in LEED for Homes (see “SIPs and green building” on page 30).
In many applications, SIPs are structurally self-sufficient and do not require additional structural framing. The oriented strand board (OSB) skins and foam core work together as an engineered system with high load-bearing capacity, including axial, transverse, racking, and diaphragm capacities. As such, they can accommodate a wide range of loads, including those from gravity, snow, high winds, and seismic activity.
Walls — As an example of SIPs’ load-bearing capacity, an 8-foot-tall, Type S panel with a 3-1/2-inch-thick foam core has an allowable axial load of 3,500 pounds per linear foot (plf), while the same height, Type S panel with a 7-1/4-inch-thick core has an allowable axial load of 4,917 plf. Higher allowable axial loads can be accommodated with SIP wall assemblies that use double 2-inch lumber splines versus standard OSB/foam splines.
The SIP manufacturer should be able to provide design load data for its specific panels based on full-scale destructive testing by accredited laboratories. This may include seismic testing and shear resistance design capacities. Depending on the manufacturer, engineers can use SIPs in seismic design categories D, E, and F to meet the most stringent earthquake requirements.
In addition to their strength, SIPs help provide a smooth and even assembly over long lengths of wall surface, since the panels come in lengths of up to 24 feet. Such walls provide a higher-quality finished appearance and a straight, solid surface for installing doors, windows, cabinets, millwork, and other finishes.
Roofs — Testing has been completed for SIPs in accordance with ASTM E 72 for transverse load capacity and deflection monitoring. The panel manufacturer can provide details on specific load capacities for roof applications with their specific SIPs.
One primary benefit of SIPs in roofs is their long clear-span capability. The large, single-piece panels can typically span up to 20 feet, reducing the need for interior columns or other intermediate structural supports. Design professionals also can use SIPs in roof structures without an engineered truss system. These capabilities work well for vaulted ceilings, large open spaces, and soaring rooflines, which are common in schools, lodging facilities, multi-housing, and other institutional and commercial building designs.
SIPs also work well in cantilevered roof eaves and gable-end overhangs extending up to 6 feet. The monolithic panels can help speed construction of such design features, compared to framing with individual components.
One application that has been growing in recent years is incorporating SIPs as part of living roofs. Because they can accommodate high loads from soil, plants, and water, and have fewer gaps than other roof-framing methods, SIPs can help meet the challenges of a green roof.
Floors — Although less common than wall and roof applications, designers can also use SIPs in floor structures where they are not supporting load-bearing walls. SIPs are most commonly used where an insulated floor system is required, such as over a crawlspace or other unheated area.
SIPs are accepted for use under the International Building Code, International Residential Code, and other model codes. The panel manufacturer can provide details on specific code evaluations, as well as supportive information, as needed, for local code officials. An example ICC-ES report is ESR-1882, referencing Premier Building Systems SIPs.
With increasing pressure being placed on design professionals to develop highly energy-efficient buildings — including ones that achieve net-zero energy use — advanced building techniques that create a tight, well-insulated envelope will become the norm. SIPs can help achieve this without sacrificing other structural and design needs.
A prime example is a school currently under construction in Zuni Pueblo, N.M. Hibbard Architecture and Planning, Chelan, Wash., designed a two-story, 18,000square-foot school with SIP walls and a roof from Fife, Wash.-based Premier Building Systems. The building will have classic adobe styling, yet the SIPs will help insulate against the daily and seasonal temperature swings in the high-elevation desert climate.
From a structural standpoint, SIPs also have been proven in a variety of demanding applications. For example, in 2008, Western Wyoming Community College opened a four-story SIP building — the tallest of its kind in North America. The 28,000-square-foot Wind River Hall uses 6-inch-thick Premier SIP walls to meet the high-gravity loads throughout the structure and protect the building from the large shear forces of the frequent Wyoming winds.
To learn more about SIP applications, contact a panel manufacturer or the Structural Insulated Panel Association at www.sips.org
Joe Pasma, P.E., is the technical manager for Premier Building Systems, a firm that develops and manufactures high-performance, energy-efficient structural insulated panels. A licensed structural engineer, Pasma has worked with SIPs for almost two decades. He can be reached at 800-275-7086 or via www.pbssips.com/bc