a comparison of structural insulated panels

8/7/2019 a comparison of structural insulated panels

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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


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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 1930s. 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

has been proven by occupancy of the house and exposure to the severe Wisconsin climate for


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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

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


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(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 R-

value 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.

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 orformaldehyde. 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 thedemand for harvesting old-growth trees.


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For example, the referenced type of SIPs panel in the paragraph above utilizes an OSB surfacecladding and an interior core of rigid polyurethane or expanded polystyrene. (EPS) that ispressure 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. Acontrolled amount of one-part urethane structural adhesive is applied between the foam coreand 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 strengthbefore the panel is removed from the press. This insures the adhesion line is notcompromised from post-press handling, storage or temperature variations. The result is apermanent bond between the foam core and the skins, which is stronger than the materials itbonds together. After manufacture, the panels are edge routed and stored in a controlledatmosphere 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 goodstructural performance using significantly less dimensional lumber. The lumber used formanufacturing OSB comes from fast growing trees that can be planted and harvested in justa few years. Reduced energy use from the efficiency of SIPs insulation also translates to theconservation of resources, and manufacturers state that the foam products used for the corematerials are environmentally benign.

The problem with the fabrication system is that it creates a product that is difficult todisassemble into its component parts for recycling.

As an alternative to the foam core, SIPs are available with a core of agriculture fibers (suchas wheat straw) that provides similar thermal and structural performance. The result is anengineered panel that provides structural framing, insulation, and exterior sheathing in asolid, one-piece component.

An experimental panel designed by CUs Bio-SIPs contains soy-based, water-blownpolyurethane foam insulation produced by Bio-Based Systems between 3/4-inch layers ofSonoboard, a lightweight honeycomb fiber panel made from recovered paper products. Thepanels have an insulating factor of approximately R-7 per inch, twice that of fiberglassblankets 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 load-

bearing 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 steelmobile home chassis.

In order to improve the ability to disassemble product components at the end of the materials lifecycle, several changes in design are recommended. These are:


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Use of mechanical fasteners to hold components together rather than reliance onadhesives

Adhesives that are located at specific points in the panels to make separation of materialseasier.

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 productcan 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
http://www.agriboard.com/http://www.arxxbuild.com/http://www.castleblock.com/protec.htmlhttp://www.r-control.com/sips.asphttp://www.murus.com/http://www.murus.com/http://www.murus.com/t.technicalEPS.htmlhttp://www.toolbase.org/techinv/techDetails.aspx?technologyID=114http://www.agriboard.com/http://www.arxxbuild.com/http://www.castleblock.com/protec.htmlhttp://www.r-control.com/sips.asphttp://www.murus.com/http://www.murus.com/http://www.murus.com/t.technicalEPS.htmlhttp://www.toolbase.org/techinv/techDetails.aspx?technologyID=114


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Table 1

STRUCTURAL INSULATED PANELS COMPARISON MATRIX

PANELTYPE

COST

PANELWIDTH

RVALUE

FIRERESISTANCE

BENDING

STRENGTH

RECYCLABLE

Oriented

Strand

Board

$2.75/ft2 4.5 25 1 hr 1000 lb/ft Yes

OSB

Wheat

Straw

$0.90/ft2 4 8 25 2.5 hrs24 load

bearingYes

ConcreteConcrete

dependant4 8 22 3 hrs

Concrete

dependantYes

Smart

Wrap

a comparison of structural insulated panels

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