Structural Insulated Panels

SIPs Provide Structure, Insulation, and Sheathing in One Package

Bird's-Eye View
Key Materials
Design Notes
Builder Tips
The Code

Bird's-Eye View

STRUCTURAL INSULATED PANELS (SIPS) ARE FAST TO ASSEMBLE. The use of a crane allows quick assembly of SIP homes. This Cape has tall wall panels, reducing heat loss at the second-floor rim joists.

Factory-made foam sandwich panels

Structural insulated panels (SIPs) consist of an insulating foam core sandwiched between an inner and outer face, typically made of oriented strand board (OSB). SIPs combine structural framing, insulation, and sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. in a single product, to be used for roofs, walls, or floors.

Panels are typically precut and delivered to the site ready for assembly with a crane. Standard thicknesses range from 4 ½ inches to 6 ½ inches, lengths up to 28 feet, and widths up to 9 feet. Some manufacturers also make custom sizes, although these cost more.

Interior faces can be made from drywall, sheet metal, or finish lumber. The foam core and exterior facings are typically glued together. One manufacturer, Winter Panel (www.winterpanel.com), produces its panels as a continuous lamination by injecting foam between the two skins and allowing the foam to expand.

An SIP roof automatically creates an unvented, conditioned attic, which can be used for living space or HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. equipment.

See below for:
TYPES OF INSULATING CORES
ADVANTAGES

Key Materials

CORNER AND SPLINE JOINTS ARE THE MOST COMMON. Electrocoated screws with broad TIN washers fasten the corner joints where dimensional lumber is installed. Midwall joints use splines that are slipped into channels routed in the foam. Splines are secured with 6d ring-shank nails; then expanding foam is inserted into the center channel to seal the joint.

Sealing the seams with caulk, adhesive, or spray foam

Manufacturer specifications for sealing SIP(SIP) Building panel usually made of oriented strand board (OSB) skins surrounding a core of expanded polystyrene (EPS) foam insulation. SIPs can be erected very quickly with a crane to create an energy-efficient, sturdy home. seams vary, but most systems require caulk, adhesive, or spray foam between panels.

In the wake of a cluster of SIP home failures in Juneau, Alaska, attributed to imperfect seam sealing, some SIP builders have decided to use redundant methods for sealing seams. In addition to spray foam between panels, some builders seal all seams from the interior with peel-and-stick butyl tape. One such tape is SIP sealing tape from R-Control (www.r-control.com).

If an SIP home is being built to meet Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. requirements, air sealing between panels must be verified using either a blower-door testTest used to determine a home’s airtightness: a powerful fan is mounted in an exterior door opening and used to pressurize or depressurize the house. By measuring the force needed to maintain a certain pressure difference, a measure of the home’s airtightness can be determined. Operating the blower door also exaggerates air leakage and permits a weatherization contractor to find and seal those leakage areas. or the completion of a visual inspection form, which requires that all interior and exterior seams be sealed with either expanding foam, manufacturer-approved sealing mastic or tape.

Design Notes

UNIQUE SHAPES DONE EFFICIENTLY. Curved edges and intricate window layouts can take a lot of extra time and material if conventionally framed. Alternatively, SIPs can be ordered right from the factory in just about any shape imaginable. The insulation in them is only interrupted at the relatively infrequent seams so thermal bridging is much lower than in a similarly shaped stud wall.

Remember, they're not sticks, they're slabs

Thicker panels are always better than thin ones. It never pays to cut corners when it comes to R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. .

Long roof spans require purlins. Some manufacturers claim that their panels can span up to 12 feet with no intermediate supports, although heavy snow loads could curtail that dimension. Longer spans require intermediate purlins, and panels require a structural ridge for support.

SIPs can create unique spaces. SIPs are often thought of as a simple replacement for wood framing. What this fails to account for, however, is that SIPs have specific properties that can and ideally should be considered in the building design. The most obvious is that they’re not sticks, they’re slabs. And they’re generally manufactured in modular panel sizes, from the conventional 4x8 on up to much larger (usually longer, not normally wider) sizes. Designing a structure to take advantage of these properties can yield a much more resource-efficient result.

Consider some other pros and cons. SIPs lend themselves to a tight envelope; demand a truly level surface to be built upon; often have predrilled cores for wiring; ideally dictate that plumbing be run in interior walls; and produce cut-offs that may be challenging to recycle. SIPs can sometimes be precut in a factory to produce a kit that can be assembled on-site, which leaves any waste with the manufacturer and not on-site.

Builder Tips

DEVIL IN THE DETAILS: Where walls meet floors an roofs is a leak potential in any type of construction. With SIPs, however, you can't bridge the connection with wall sheathing, so it's important to use gaskets and sealants.

Wrestling with unwieldy panels

Pulling panels tightly together — especially large roof panels — can be tricky. Some panels weigh as much as 800 pounds. Experienced installers resort to beater blocks, sledgehammers, nylon ratchet straps, large wrecking bars, and come-alongs to join panels tightly.

Pay attention to air-sealing details. To avoid air leakage that can lead to condensation and rot, SIP(SIP) Building panel usually made of oriented strand board (OSB) skins surrounding a core of expanded polystyrene (EPS) foam insulation. SIPs can be erected very quickly with a crane to create an energy-efficient, sturdy home. seams must be meticulously sealed, so manufacturer's sealing instructions must be followed diligently.

Running wires. Panels usually come with a preformed chase for electrical wiring, but boxes for switches and outlets must be routed into the surface and then sealed with foam. Careful wiring plans can reduce the need to gouge out installed panels, and including baseboard raceways for wiring just about eliminates the problem while making future upgrades and changes easier. Plumbing runs should be contained in conventionally framed interior partitions, not in exterior walls.

Can I cut the panels on-site? Minor field modifications to panels are possible, but extensive changes are not recommended because they could affect a panel's strength.

The Code

Be sure to check with your local code official

Currently, there are no prescriptive design guidelines in the IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code. for SIPs, so a local code official may require that an architect or engineer sign off on the design. Most panel producers provide engineering services and drawings to help facilitate the approval process.

OTHER CONSIDERATIONS

Timber frames and SIPs
SIPs work fine on their own, but they are often used to skin a timber-frame home. This may seem redundant because of the structural quality of SIPs, but pairing the two construction types can create open spaces that are unmatched by most other home styles. You could make the best of the situation with passive solar heating, natural lighting, and an adaptable floor plan. Reclaimed timber could also make the combination environmentally acceptable.

A COST COMPARISON

The cost of SIPs for a 1000-square-foot house built in West Virginia in 2005 was $13,500. That’s more than double the cost of framing lumber and insulation for a similarly sized house built using stud framing. However, the final project cost was $110,000, so after adjusting for a less-expensive HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. system, the homeowners paid only a 6% premium for SIPs. With tax breaks and reduced heating and cooling loads, the savings averaged $120 per month. After two years and eight months, the homeowners broke even on their investment. If they live in the home for 10 more years, they will have an overall savings of $14,400. If they put the money back into their mortgage, the 30-year term would be reduced to 20 years.
— from Fine Homebuilding

GREEN POINTS

LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. -H Wall system influences thermal performance, potentially affecting 3 to 5 points in EA1 (Energy & Atmosphere), EA2, and/or EA3; up to 3 points for SIPs in MR1 (Materials & Resources). MR2.2 offers points for environmentally preferable wall framing and insulation materials.

NGBSNational Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions. Under Chapter 7, "Energy Efficiency": SIPs can contribute to superior thermal performance, which could mean up to 36 points based on the NGBS prescriptive path (703), or up to 120 points based on the performance path (702). Under Chapter 6, "Resource Efficiency": 4 points for each major building assembly (floor, wall, roof) that is made from a premanufactured system (601.5).

ABOUT SIPs

A well-established building system
SIPs have a long history in the U.S. housing industry. Early versions were developed in the mid '30s at the Forest Products Laboratory, and the first foam-core panel was produced more than a half century ago. SIPs have never quite broken into the housing mainstream, but they offer a number of advantages over conventional stick framing.

SIP construction is more expensive than standard frame construction, but because the resulting building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. is tighter and insulation values potentially higher, using them may make it possible to downsize heating and cooling equipment. Lower operating costs over the life of the building should mean a net gain over conventional construction.

TYPES OF INSULATING CORES

Most panels have foam cores

Expanded polystyrene.
By far the most common type of foam used in panels, expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.) has an R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of 3.6 per inch. Its low melting point is an advantage to builders who need to make field alterations with heated cutting tools. It has a fairly high perm rating of 3. EPS is the least expensive option.

Polyurethane and polyisocyanurate.

Nearly identical chemically, these foams have an R-value of about 6 or 7 per inch. They are more expensive and somewhat less widely available than EPS. Their higher melting point means that recesses for wiring and boxes must be drilled or routed instead of cut with a heated tool. They have a perm rating of 1, making them effective vapor barriers.

Extruded polystyrene.
At least two manufacturers make extruded polystyrene (XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.) panels. The foam is more expensive than EPS but has an R-value of 5 per inch and a perm rating of 1. It also has a high melting point. The two companies are Foard Panel of New Hampshire and Murus of Pennsylavania.

Wheat and rice straw. At least one manufacturer now produces an SIP product that has a core of rice and wheat straw instead of petroleum-based foam. Insulating values are lower (roughly 3.2 per inch), so thicker panels will be needed to achieve a given wall R-value. Agriboard Industries says that panels make use of agricultural waste that would otherwise be burned.

MORE ABOUT SIPs

When compared to standard stick-framing, SIPs have a number of advantages

Speed of construction. Panels are made in a factory and trucked to the construction site ready for installation. With the help of a crane or a few strong backs, wall sections can be assembled quickly, reducing drying time from weeks or months to a matter of days.

Fewer air leaks. Unlike conventionally framed walls, SIPs have no wall cavities and therefore fewer opportunities for energy losses due to internal convection. Continuous insulation means that SIP houses have much less air infiltration than standard framed houses. However, supertight construction makes whole-house ventilation all the more important. Careful workmanship is key to eliminating potential air leaks at joints between panels — leaks that could cause condensation and structural damage, especially in roof panels.

Reduced thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. . Virtually the entire core is insulation. With dimensional lumber significantly reduced, energy losses due to thermal bridging are lower.

High R-values. Standard wall sections are made in thicknesses of up to 6 ½ inches. When the core is made from polyurethane foam, the wall’s R-value is roughly twice as high as a framed 2x6 wall insulated with fiberglass batts.

Great strength. Bonding the foam to the outer panels creates a strong assembly, not unlike that of an I-beam. Panels are highly resistant to racking and shear loads and can withstand high winds and seismic activity.