Are Structural Insulated Panels More Expensive?

Building with SIPs generally costs about the same as building with wood frame construction when you factor in the labor savings resulting from shorter construction time and less jobsite waste. Other savings are realized because smaller heating and cooling systems are required with SIP construction.
SIPs do an impressive job of slowing down the transfer of heat, air, and vapor through the assembly. They also dramatically reduce the drying potential of the enclosure, lessening its ability to recover from inadvertent water intrusion. Such an airtight assembly with great thermal resistance can result in a high-performance and durable enclosure if detailed and built correctly.

DESCRIPTION

Structural insulated panels are composed of an insulated foam core between two rigid board sheathing materials. The foam core is generally one of the following: expanded polystyrene (EPS), extruded polystyrene (XPS), and polyurethane foam (PUR). With EPS and XPS foam, the assembly is pressure laminated together. With PUR and PIR, the liquid foam is injected and cured under high pressure.
The most common sheathing boards are oriented strand boards (OSB). Other sheathing materials include: sheet metal, plywood, fiber-cement siding, magnesium-oxide board, fiberglass mat gypsum sheathing, and composite structural siding panels.
Each sheathing material and foam type has its benefits and drawbacks. The type of SIPs selected depends upon the building type and site conditions. The following tables outline the benefits and drawbacks of the most common sheathing and foam types.

Table 1: Sheathing Type Chart

SHEATHING TYPE	BENEFITS	DRAWBACKS
Oriented Strand Board (OSB)	Load bearing; readily available; tested; large panel size up to 8' x 24'	Subject to mold and a reduction in structural capacity if exposed to moisture; not fire resistant; must be treated for termites; difficult substrate for most common joint tapes
Sheet Metal	Reistant to mold; can be load-bearing; very light; unlimited lengths when made from coil stock	Must be galvanized or stainless steel; not load bearing
Plywood	Lateral strength	Availability; price; limited panel size; subject to mold and reduced structural capacity if exposed to moisture for a prolonged period of time; not fire resistant; must be treated for termites
Fiber Cement Siding	Resistant to mold, termites, and fire	Availability; weight; testing; limited panel size
Magnesium Board	Resistant to mold, termites, and fire	Availability; testing; limited panel size
Fiberglass Mat Gypsum Sheathing	Resistant to termites and fire	Not structural; limited panel size
Composite Structural Siding Panels	Resistant to mold and termites; pre-primed materials available	Not fire resistant

Table 2: Core Type Chart

FOAM CORE	BENEFITS	DRAWBACKS
Expanded Polystyrene (EPS)	Least expensive; thickness options are only limited by the foam manufacturer; availability; fastest to modify in field; most benign blowing agent	Produced with HBCD*
Extruded Polystyrene (XPS)	Strength; water resistant	Availability; produced with HBCD*
Polyurethane Foam (PUR)	Highest R-value/inch; strength, water resistant	Most expensive; harder to modify thickness limitations; creep; availability; produced with chlorinated phosphate flame retardants**

*HBCD: hexabromocyclododecane - a brominated fire retardant classified by the European Union (REACH program) as persistant, bioaccumulative, and toxic (PBT).
**Not as hazardous as most brominated flame retardants, but health and environmental concerns still exist.
Source: BuildingGreen Insulation Report

Table 3: Foam Technical Data

FOAM TYPE*	EPS FOAM	XPS FOAM	PUR FOAM
Density in Panel (lb/ft3)	0.90	1.5	2.3 – 2.5
Compressive Strength @ 10% deformation (psi)	10	20	35
R-value/in @ 75° F	3.6	5.0	6.54
Permeance per inch	5	1.1	2.00
Common Fire Retardant	HBCD	HBCD	TCPP
Common Fire Rating Class	1	1	1
Common Blowing Agent	Pentane	HFC—134a	HFC—245fa

* Most SIP manufacturers use a 0.95 minimum density.