Structural insulated panel
Encyclopedia
Structural insulated panels (or structural insulating panels), SIPs, are a composite building material
. They consist of an insulating layer of rigid polymer foam sandwiched between two layers of structural board. The board can be sheet metal, plywood, cement or oriented strand board
(OSB) and the foam either expanded polystyrene foam
(EPS), extruded polystyrene foam (XPS) or polyurethane foam.
SIPs share the same structural properties as an I-beam or I-column. The rigid insulation core of the SIP acts as a web, while the OSB sheathing exhibits the same properties as the flanges. SIPs combine several components of conventional building, such as studs and joists, insulation, vapor barrier and air barrier. They can be used for many different applications, such as exterior wall, roof, floor and foundation systems.
(FPL) in Madison, Wisconsin
as part of an U.S. Forest Service attempt to conserve forest resources. In 1937, a small stressed-skin house was constructed and garnered enough attention to bring in First Lady
Eleanor Roosevelt
to dedicate the house. In a testament to the durability of such panel structures, it has endured the severe Wisconsin climate and was used by University of Wisconsin–Madison
as a day care center up until 1998 when it was removed to make way for a new Pharmacy School building. With the success of the stress skinned panels, it was suggested stronger skins could take all of the structural load and eliminate the frame altogether.
Thus in 1947, structural insulated panel development began with corrugated paperboard cores were tested with various skin materials of plywood, tempered hardboard and treated paperboard. The building was dismantled in 1978 and most of the panels retained their original strength with the exception of paperboard which is unsuited to outdoor exposure. Panels consisting of polystyrene core and paper overlaid with plywood skins were used in a building in 1967 and the panels have performed well to the present day.
SIP panel systems were used by Woods Constructors of Santa Paula, California in their homes and apartments from 1965 until 1984. This work was the basis for John Thomas Woods, Paul Flather Woods, John David Woods, and Frederick Thomas Woods when they used a similar concept to patent the Footing Form for Modular homes (US Patent #4817353) issued on April 4, 1989. Numerous homes in Santa Paula, Fillmore, Palm Springs, and surrounding areas use SIP panels as the primary method of construction. The design was awarded approval from (then) ICBO and SBCCI, now ICC.
such as Hardibacker, and even exotic materials like stainless steel, fiber-reinforced plastic, and magnesium oxide. Some SIPs use fiber-cement
or plywood sheets for the panels, and agricultural fiber, such as wheat straw, for the core.
The third component in SIPs is the spline or connector piece between SIP panels. Dimensional lumber is commonly used but creates thermal bridging and lowers insulation values. To maintain higher insulation values through the spline manufacturers use Insulated Lumber, Composite Splines, Mechanical Locks, Overlapping OSB Panels, or other creative methods. Depending on the method selected other advantages such as full nailing surfaces or increased structural strength may become available.
The cost of SIPs are higher than the materials for a comparable framed building in the United States, however this may not be true elsewhere. A well-built home using SIPs will have a tighter building envelope and the walls will have higher insulating properties, which leads to fewer drafts and a decrease in operating costs. Also, due to the standardized and all-in-one nature of SIPs, construction time can be less than a frame home, as well as requiring fewer tradesmen. The panels can be used as floor, wall, and roof, with the use of the panels as floors being of particular benefit when used above an uninsulated space below. As a result, the total life-cycle cost of a SIP-constructed building will, in general, be lower than a conventional framed one, some even get up to 40% lifetime savings. Whether this benefit is realized on total construction cost alone (materials and labor) appears to depend on the circumstances, including local labor conditions and the degree to which the building design is optimized for one or the other technology.
An OSB skinned system structurally outperforms conventional stick framed construction in some cases; primarily in axial load strength. SIPs maintain similar versatility to stick framed houses when incorporating custom designs. Also, since SIPs work as framing, insulation, and exterior sheathing, and can come precut from the factory for the specific job, the exterior building envelope can be built quite quickly.
When tested under laboratory conditions, the SIP, included in a wall, foundation, floor, or roof system, is installed in a steady-state (no air infiltration) environment; systems incorporating fiberglass insulation are not installed in steady-state environments as they require ventilation to remove moisture.
With the exception of structural metals, such as steel, all structural materials creep
over time. In the case of SIPs, the creep potential of OSB faced SIPs with EPS or polyurethane foam cores has been studied and creep design recommendations exist. The long-term effects of using unconventional facing and core materials require material specific testing to quantify creep design values.
EPS is the most common of the foams used and has an R-value
(thermal resistance) of about 4 K·m2/W per 25 mm thickness, which would give the 3.5 inches (88.9 mm) of foam in a 4.5 inches (114.3 mm) panel an R value of 13.8 (caution: extrapolating R-values over thickness may be imprecise due to non-linear thermal properties of most materials). This at face value appears to be comparable to an R-13 batt of fiberglass, but because in a standard stick frame house there is significantly more wall containing low R value wood that acts as a cold bridge, the thermal performance of the R-13.8 SIP wall will be considerably better.
The air sealing features of SIP homes resulted in the Environmental Protection Agency's Energy Star program to establish an inspection protocol in lieu of the typically required blower door test to assess the home's air leakage. This serves to speed the process and save the builder/homeowner money.
Aside from these non-proprietary standards, the SIP industry has relied heavily on proprietary code evaluation reports. ICC-ES issues numerous evaluation reports, most commonly to major manufacturers such as R-Control. In early 2009, SIPA partnered with NTA Inc
, a product certification agency, to produce the first industry wide code report which is available to all SIPA members who qualify. Unlike previous code reports, the prescriptive provisions provided in the SIPA code report are derived from an engineering design methodology which permits the design professional to consider loading conditions not addressed in the code report.
While the use of SIPs has many potential benefits, caution must be used to ensure that the lack of consideration for such effects does not lead to the creation of ill-designed structures. Use of an experienced architect or designer will minimize this potential issue.
Building material
Building material is any material which is used for a construction purpose. Many naturally occurring substances, such as clay, sand, wood and rocks, even twigs and leaves have been used to construct buildings. Apart from naturally occurring materials, many man-made products are in use, some more...
. They consist of an insulating layer of rigid polymer foam sandwiched between two layers of structural board. The board can be sheet metal, plywood, cement or oriented strand board
Oriented strand board
Oriented strand board, also known as OSB and SmartPly , is an engineered wood product formed by layering strands of wood in specific orientations. In appearance, it may have a rough and variegated surface with the individual strips Oriented strand board, also known as OSB (UK) and SmartPly (UK &...
(OSB) and the foam either expanded polystyrene foam
Polystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
(EPS), extruded polystyrene foam (XPS) or polyurethane foam.
SIPs share the same structural properties as an I-beam or I-column. The rigid insulation core of the SIP acts as a web, while the OSB sheathing exhibits the same properties as the flanges. SIPs combine several components of conventional building, such as studs and joists, insulation, vapor barrier and air barrier. They can be used for many different applications, such as exterior wall, roof, floor and foundation systems.
History
Although foam-core panels gained attention in the 1970s, the idea of using stress skinned panels for construction began in the 1930s. Research and testing of the technology was done primarily by Forest Products LaboratoryForest Products Laboratory
The Forest Products Laboratory is the national research laboratory of the United States Forest Service, which is part of USDA. Since its opening in 1910, the FPL has provided scientific research on wood, wood products and their commercial uses in partnership with academia, industry, tribal, state,...
(FPL) in Madison, Wisconsin
Madison, Wisconsin
Madison is the capital of the U.S. state of Wisconsin and the county seat of Dane County. It is also home to the University of Wisconsin–Madison....
as part of an U.S. Forest Service attempt to conserve forest resources. In 1937, a small stressed-skin house was constructed and garnered enough attention to bring in First Lady
First Lady
First Lady or First Gentlemanis the unofficial title used in some countries for the spouse of an elected head of state.It is not normally used to refer to the spouse or partner of a prime minister; the husband or wife of the British Prime Minister is usually informally referred to as prime...
Eleanor Roosevelt
Eleanor Roosevelt
Anna Eleanor Roosevelt was the First Lady of the United States from 1933 to 1945. She supported the New Deal policies of her husband, distant cousin Franklin Delano Roosevelt, and became an advocate for civil rights. After her husband's death in 1945, Roosevelt continued to be an international...
to dedicate the house. In a testament to the durability of such panel structures, it has endured the severe Wisconsin climate and was used by University of Wisconsin–Madison
University of Wisconsin–Madison
The University of Wisconsin–Madison is a public research university located in Madison, Wisconsin, United States. Founded in 1848, UW–Madison is the flagship campus of the University of Wisconsin System. It became a land-grant institution in 1866...
as a day care center up until 1998 when it was removed to make way for a new Pharmacy School building. With the success of the stress skinned panels, it was suggested stronger skins could take all of the structural load and eliminate the frame altogether.
Thus in 1947, structural insulated panel development began with corrugated paperboard cores were tested with various skin materials of plywood, tempered hardboard and treated paperboard. The building was dismantled in 1978 and most of the panels retained their original strength with the exception of paperboard which is unsuited to outdoor exposure. Panels consisting of polystyrene core and paper overlaid with plywood skins were used in a building in 1967 and the panels have performed well to the present day.
SIP panel systems were used by Woods Constructors of Santa Paula, California in their homes and apartments from 1965 until 1984. This work was the basis for John Thomas Woods, Paul Flather Woods, John David Woods, and Frederick Thomas Woods when they used a similar concept to patent the Footing Form for Modular homes (US Patent #4817353) issued on April 4, 1989. Numerous homes in Santa Paula, Fillmore, Palm Springs, and surrounding areas use SIP panels as the primary method of construction. The design was awarded approval from (then) ICBO and SBCCI, now ICC.
Materials
SIPs are most commonly made of OSB panels sandwiched around a foam core made of expanded polystyrene (EPS), extruded polystyrene (XPS) or rigid polyurethane foam, but other materials can be used, such as plywood, pressure-treated plywood for below-grade foundation walls, steel, aluminum, cement boardCement board
A cement board is a combination of cement and reinforcing fibers formed into 4 foot by 8 foot sheets , 1/4 to 1/2 inch thick that are typically used as a tile backing board...
such as Hardibacker, and even exotic materials like stainless steel, fiber-reinforced plastic, and magnesium oxide. Some SIPs use fiber-cement
Fiber cement siding
Fiber cement siding is a building material used to cover the exterior of a building in both commercial and domestic applications.-Usage:...
or plywood sheets for the panels, and agricultural fiber, such as wheat straw, for the core.
The third component in SIPs is the spline or connector piece between SIP panels. Dimensional lumber is commonly used but creates thermal bridging and lowers insulation values. To maintain higher insulation values through the spline manufacturers use Insulated Lumber, Composite Splines, Mechanical Locks, Overlapping OSB Panels, or other creative methods. Depending on the method selected other advantages such as full nailing surfaces or increased structural strength may become available.
Benefits and drawbacks
The use of SIPs brings many benefits and some drawbacks compared to a conventional framed building.The cost of SIPs are higher than the materials for a comparable framed building in the United States, however this may not be true elsewhere. A well-built home using SIPs will have a tighter building envelope and the walls will have higher insulating properties, which leads to fewer drafts and a decrease in operating costs. Also, due to the standardized and all-in-one nature of SIPs, construction time can be less than a frame home, as well as requiring fewer tradesmen. The panels can be used as floor, wall, and roof, with the use of the panels as floors being of particular benefit when used above an uninsulated space below. As a result, the total life-cycle cost of a SIP-constructed building will, in general, be lower than a conventional framed one, some even get up to 40% lifetime savings. Whether this benefit is realized on total construction cost alone (materials and labor) appears to depend on the circumstances, including local labor conditions and the degree to which the building design is optimized for one or the other technology.
An OSB skinned system structurally outperforms conventional stick framed construction in some cases; primarily in axial load strength. SIPs maintain similar versatility to stick framed houses when incorporating custom designs. Also, since SIPs work as framing, insulation, and exterior sheathing, and can come precut from the factory for the specific job, the exterior building envelope can be built quite quickly.
When tested under laboratory conditions, the SIP, included in a wall, foundation, floor, or roof system, is installed in a steady-state (no air infiltration) environment; systems incorporating fiberglass insulation are not installed in steady-state environments as they require ventilation to remove moisture.
With the exception of structural metals, such as steel, all structural materials creep
Creep (deformation)
In materials science, creep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses. It occurs as a result of long term exposure to high levels of stress that are below the yield strength of the material....
over time. In the case of SIPs, the creep potential of OSB faced SIPs with EPS or polyurethane foam cores has been studied and creep design recommendations exist. The long-term effects of using unconventional facing and core materials require material specific testing to quantify creep design values.
Dimensions and characteristics
In the United States, SIPs tend to come in sizes from 4 feet (1.22 m) to 24 feet (7.32 m) in width. Elsewhere, typical product dimensions are 300, 600, or 1,200 mm wide and 2.4, 2.7, and 3 m long, with roof SIPs up to 6 m long. Smaller sections ease transportation and handling, but the use of the largest panel possible will create the best insulated building. At 15−20 kg/m², longer panels can become difficult to handle without the use of a crane to position them, and this is a consideration that must be taken into account due to cost and site limitations. Also of note is that when needed for special circumstances longer spans can often be requested, such as for a long roof span. Typical U.S. height for panels is eight or nine feet (2.44 to 2.75 m). Panels come in widths ranging from 4 to 12 inches thick and a rough cost is $4–$6/ft2 in the U.S. In 4Q 2010, new methods of forming radius, sine curve, arches and tubular SIPs were commercialized. Due to the custom nature and technical difficulty of forming and curing specialty shapes, pricing is typically three or four times that of standard panels per foot.EPS is the most common of the foams used and has an R-value
R-value (insulation)
The R-value is a measure of thermal resistance used in the building and construction industry. Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux through it or R = \Delta T/\dot Q_A.The R-value being discussed is the unit thermal resistance...
(thermal resistance) of about 4 K·m2/W per 25 mm thickness, which would give the 3.5 inches (88.9 mm) of foam in a 4.5 inches (114.3 mm) panel an R value of 13.8 (caution: extrapolating R-values over thickness may be imprecise due to non-linear thermal properties of most materials). This at face value appears to be comparable to an R-13 batt of fiberglass, but because in a standard stick frame house there is significantly more wall containing low R value wood that acts as a cold bridge, the thermal performance of the R-13.8 SIP wall will be considerably better.
The air sealing features of SIP homes resulted in the Environmental Protection Agency's Energy Star program to establish an inspection protocol in lieu of the typically required blower door test to assess the home's air leakage. This serves to speed the process and save the builder/homeowner money.
Standardization and design
The International Building Code references APA, Plywood Design Specification 4—Design & Fabrication of Plywood Sandwich Panels for the design of SIPs. This document addressed the basic engineering mechanics of SIP panels but does not provide design properties for the panels provided by any specific manufacturer. In 2007, prescriptive design provisions for OSB faced SIPs were first introduced in the 2006 International Residential Code. These provisions provide guidance on the use of SIPs as walls panels only.Aside from these non-proprietary standards, the SIP industry has relied heavily on proprietary code evaluation reports. ICC-ES issues numerous evaluation reports, most commonly to major manufacturers such as R-Control. In early 2009, SIPA partnered with NTA Inc
NTA Inc
NTA Inc is a nationally recognized testing laboratory and third party certification agency headquartered in Nappanee, Indiana, USA.- About NTA :NTA evaluates and certifies products for the residential and commercial building industry....
, a product certification agency, to produce the first industry wide code report which is available to all SIPA members who qualify. Unlike previous code reports, the prescriptive provisions provided in the SIPA code report are derived from an engineering design methodology which permits the design professional to consider loading conditions not addressed in the code report.
While the use of SIPs has many potential benefits, caution must be used to ensure that the lack of consideration for such effects does not lead to the creation of ill-designed structures. Use of an experienced architect or designer will minimize this potential issue.
See also
- Nano HouseNano HouseThe Nano House was named to be the worlds smallest sustainable house.The Nano Living System is a Swiss made "green" pre-engineered concept for residential use that presents an innovative and sustainable architectural proposition...
- NTA IncNTA IncNTA Inc is a nationally recognized testing laboratory and third party certification agency headquartered in Nappanee, Indiana, USA.- About NTA :NTA evaluates and certifies products for the residential and commercial building industry....
— Third Party Testing Laboratory and Certification Agency for the SIP Industry