Insulated Panels 1
A Comparison of Structural Insulated Panels
Linda Stevenson, Marc McIntee, Craig Roberts
University of Florida
In partial fulfillment of the requirements for BCN 6586
Dr. Charles J. Kibert
February 21, 2006
Insulated Panels 2
History
As an alternative to traditional methods of construction, Structural Insulated Paneling has
become more popular in recent years. With so much emphasis on energy saving, SIPs appeal to
the consumer that is conscious of heat transfer. Structural insulated panels have been proven to
be appropriate in all geographic areas. They are particularly effective in extreme thermal climate
zones such as high mountain, snow country and deserts. The high thermal insulative value and
minimum thermal bridging composition of panels make them extremely energy efficient. Panels
have also withstood severe structural loading conditions such as the Kobe earthquake in Japan
and Hurricane Andrew in Florida. The unique double shear configuration of structural insulated
panel technology, which is the basis of most structural insulated panels, makes them unusually
strong in extreme structural loading conditions.
The timeline of SIPs starts about 60 years ago with the conception of an idea to use
stressed-skin panels in building construction. Much of the engineering and durability testing
over the 60-year period was conducted at the Forest Products Laboratory (FPL) in Madison,
Wisconsin. The concept of using skins to carry a portion of structural loads in a building was
first implemented in the 1930’s. The main reason for the research was to reduce the amount of
lumber needed in construction. The idea is, that if skins were rigidly glued to a thick core, they
would take most of the structural loads. With this in mind, a building panel with smaller than
usual framing members glued to interior and exterior skins was planned and designated as
“stressed-skin” construction. FPL tested the concept and proceeded to build a small house in
1937. This stressed-skin house attracted a great deal of attention and First Lady Eleanor
Roosevelt personally dedicated the house on FPL grounds. Durability of the stressed-skin panels
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has been proven by occupancy of the house and exposure to the severe Wisconsin climate for
nearly 60 years. A second house was built in 1947 to test the concept of having the skins take all
of the loads and thus eliminate framing completely. This test structure was heated, humidified,
exposed to Wisconsin weather, and underwent a series of changes of insulating material over the
next 31 years. In 1978, the FPL stressed-skin structure was totally disassembled and all panels
were destructively tested by loading to failure. Most of the panels retained both their stiffness
and strength as compared to panels of identical composition tested at the time of fabrication. At
the time of its inception, the method was acclaimed as the building technique of the future. That
future has finally arrived as can be seen in the rapidly growing structural insulated panel industry.
Since the current panel industry is using rigid foam cores that have outstanding insulating
characteristics, the industry has chosen to call them “structural insulated panels.
A Comparison of Structural Insulated Panels
Structural insulated paneling has several benefits, which include fast installation, increased
R-value, increased strength and more ease in deconstruction and reuse. There are several
different structural insulated panels on the market and no comparison between them as which
will be the best to use depending on application. Four different types of structural insulated
panels will be compared which are oriented strand board (OSB), concrete insulated panels (CIP),
OSB insulated panels with wheat straw as the core and smart wrap which is a brand name for a
type of structural insulated panel. Agriboard is a new OSB structural insulated panel, which uses
a core that is, not form but is wheat straw. The agriboard panel can be provided in thickness of
four to eight inches with a panel weight of nine to fourteen pounds per square foot. The R-value
of the panels range from thirteen to twenty five and has a load bearing of eight to twenty four
Insulated Panels 4
feet. The panels have a fire resistance of two and one half hours. Standard OSB structural
insulated panel uses a core that is foam which depending on the type of foam used could have
ozone-depleting chemicals associated with its production and use. Molded expanded polystyrene
(MEPS) is a particular foam insulation that has no ozone depleting chemicals associated with its
production and use. It is four to eight inches thick with a panel weight of 3.75 ponds per square
foot with a bending strength of 1000 ft/lb. The cost of this panel is $2.75 per square foot.
Insulated concrete wall panels (CIP) are constructed with two flame resistance panels of
expanded polystyrene (EPS) connected by high-density foam webs that are molded in place and
can receive reinforcing steel bars. The concrete is poured between the panels to form the
insulated panels. The load bearing strength is dependant on the strength of the concrete. The Rvalue of the insulated panels is rated at R-22. The fire resistance rating is here hours with a
thickness of four to eight inches. SmartWrap is made of several layers including a substrate,
printed and laminated layers, all of which are roll-coated into a single composite film. A
polyester film substrate protects from rain and wind. To moderate temperature, SmartWrap
contains microcapsules of phase change materials that are embedded into a polymer resin and
then extruded into a film. They provide latent heat storage for thermal moderation by absorbing,
storing, or releasing heat as they change state. For lighting and information display, SmartWrap
uses Organic Light Emitting Diode (OLED) technology that is based on organic molecules that
emit light when an electric current is applied. And for power, SmartWrap relies on solar energy
that is collected in thin film silicon solar cells. This energy is then used to power the OLED
technology. Table 1 has the comparison stats of the structural insulated panels discussed above.
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Sustainable design and dematerialization
While many structural insulated panel (SIP) products claim to be “environmentally responsible”,
a closer study of the assembly methods reveals the difficulty in recycling these materials.
Environmentally Responsible: Murus EPS foam contains no CFCs, HCFCs, HFCs or
formaldehyde. The EPS core is recyclable, relieving the drain on our petroleum reserves. Use
of Murus EPS panels reduces the use of dimensional lumber, thereby reducing the demand
for harvesting old-growth trees.
For example, the referenced type of SIPs panel in the paragraph above utilizes an OSB surface
cladding and an interior core of rigid polyurethane or expanded polystyrene. (EPS) that is
pressure laminated to the skin materials with a one –part polyurethane adhesive.
Expanded Polystyrene (EPS) Panels
The Murus EPS panel is manufactured using the "Pressure Laminating method" or PLM. A
controlled amount of one-part urethane structural adhesive is applied between the foam core
and the skins and is then placed under pressure in a press while the adhesive reacts and cures.
While the panels are under pressure, the adhesive reaches about 90% of its total strength
before the panel is removed from the press. This insures the adhesion line is not
compromised from post-press handling, storage or temperature variations. The result is a
permanent bond between the foam core and the skins, which is stronger than the materials it
bonds together. After manufacture, the panels are edge routed and stored in a controlled
atmosphere for a 24-hour period. The panels are then ready for shipment to the building site.
The claim of environmentally friendliness of this type of technology is described below:
Use of SIPs panels can help conserve scarce timber resources, since they provide good
structural performance using significantly less dimensional lumber. The lumber used for
manufacturing OSB comes from fast growing trees that can be planted and harvested in just a
few years. Reduced energy use from the efficiency of SIPs insulation also translates to the
conservation of resources, and manufacturers state that the foam products used for the core
materials are environmentally benign.
The problem with the fabrication system is that it creates a product that is difficult to disassemble
into its component parts for recycling.
As an alternative to the foam core, SIPs are available with a core of agriculture fibers (such as
wheat straw) that provides similar thermal and structural performance. The result is an
engineered panel that provides structural framing, insulation, and exterior sheathing in a
solid, one-piece component.
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An experimental panel designed by CU’s Bio-SIPs contains soy-based, water-blown
polyurethane foam insulation produced by Bio-Based Systems between 3/4-inch layers of
Sonoboard, a lightweight honeycomb fiber panel made from recovered paper products. The
panels have an insulating factor of approximately R-7 per inch, twice that of fiberglass
blankets or batts or loose-fill cellulose (R-value is a measure of resistance to heat transfer,
with higher numbers connoting better insulation). Full-scale versions of the panels
(measuring 8 feet tall, 4 feet wide, and 7 inches thick) were strong enough to use as loadbearing walls in the solar house, where they provide insulation values of approximately R-36.
The soy foam was also used in the house ceilings and as insulation beneath its steel mobile
home chassis.
In order to improve the ability to disassemble product components at the end of the materials life
cycle, several changes in design are recommended. These are:



Use of mechanical fasteners to hold components together rather than reliance on
adhesives
Adhesives that are located at specific points in the panels to make separation of materials
easier.
Use of agricultural products for the panel layers that can be more easily recycled.
Similar disassembly problems exist for concrete – foam panel systems. The resulting product
can be crushed and perhaps used for aggregate in making new concrete.
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References
Agriboard Industries (2006). Environmental Engineered Structural Insulated Panel. Retrieved
February 06, 2006 from http://www.agriboard.com
Arxx (2006). Walls and Foundations. Retrieved February 10, 2006 from
http://www.arxxbuild.com
Protech (2006). Concrete Structural Insulated Panel System. Retrieved February 09, 2006 from
http://www.castleblock.com/protec.html
Structural Insulated Panels (2006). http://www.r-control.com/sips.asp
Product Literature for Murus SIP (Sweets Catalog 2006) section 061200. http://www.murus.com/
http://www.murus.com/
http://www.murus.com/t.technicalEPS.html
http://www.toolbase.org/techinv/techDetails.aspx?technologyID=114
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Table 1
$0.90/ft2
4 – 8”
25
2.5 hrs
RECYCLABLE
1 hr
STRENGTH
25
BENDING
R VALUE
4.5”
RESISTANCE
PANEL WIDTH
$2.75/ft2
FIRE
COST
PANEL TYPE
STRUCTURAL INSULATED PANELS COMPARISON MATRIX
Oriented
Strand
1000 lb/ft
Yes
Board
OSB
24’ load
Wheat
Yes
bearing
Straw
Concrete
dependant
Smart
Wrap
Concrete
4 – 8”
Concrete
22
3 hrs
Yes
dependant