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Frequently Asked Questions About Structural Insulated Panels
Designing & Planning with SIPs
ACME Panel Company's structural insulated panels (SIPs) are high performance building panels used in floors, walls, and roofs for residential and light commercial buildings. The panels are typically made by sandwiching a core of rigid foam plastic insulation between two structural skins of oriented strand board (OSB). Other skin material can be used for specific purposes. SIPs are manufactured under factory controlled conditions and can be custom designed for each home. The result is a building system that is extremely strong, energy efficient, and cost effective that replaces traditional framing, insulation, and sheeting. Building with SIPs will save you time, money, and labor.
The structural characteristics of SIPs are similar to that of a steel I-Beam. The OSB skins act as the flange of the I-beam, while the rigid foam core provides the web. This design gives SIPs an advantage at handling in plane compressive loads. SIPs can be engineered for most applications.
Residential building code requires that foam insulation be separated from the interior of the building by a material that remains in place for at least 15 minutes of fire exposure. Structural insulated panels faced with 0.5” gypsum drywall meet this requirement.
An airtight SIP building envelope forms the basis of a successful mold control strategy. The extremely low levels of air infiltration in SIP buildings allow for incoming air to be provided in controlled amounts by air handling equipment. Proper dehumidification of incoming air following ASHRAE standards will create an environment where mold physically cannot grow. In addition to creating an airtight structure, SIPs are solid and free of any cavities in the wall where moisture can condense and cause unseen mold growth.
No more than traditional framing. Although termites do not feed on the foam panel cores, there have been instances in which panel cores have been hollowed out by these insects and used as a nesting ground. Termites may be deterred through the use of a specifically designed steel mesh. Both these treatments are highly effective, but they are not a substitute for careful termite prevention and maintenance, as with any other wood structures.
If panels are damaged, a structural engineer needs to assess the damage to determine what is cosmetic and what is structural. If the damage is only cosmetic, then the source of moisture must be determined and fixed, whether it is from inside or outside. If the damage is structural, then the source of the problem must be identified and a structural solution to the problem must be found. That can be done by either a site modification of the panels or replacement of the panels, depending on the extent of the damage. In the event that panels are damaged, the manufacturer and installer of the panels should be notified.
Energy efficient structural insulated panels are one of the most environmentally responsible building systems available. A SIP building envelope provides high levels of insulation and is extremely airtight, meaning the amount of energy used to heat and cool a home can be cut by up to 50%. The energy that powers homes and commercial buildings is responsible for a large portion of greenhouse gasses emitted into the atmosphere. By reducing the amount of energy used in buildings, architects, builders, and homeowners can contribute to a clean environment for the future.
The insulation used in SIPs is a lightweight rigid foam plastic composed of 98% air and requires only a small amount of petroleum to produce. The foam insulation used in panel cores is made using a non-CFC blowing agent that does not threaten the earth’s ozone layer.
Since SIPs are prefabricated in the factory, there is less jobsite waste that needs to be landfilled. Factory fabrication is done using optimization software and we recycle factory scrap to make other foam products.
The tightness of the SIP building envelope prevents air from gaining access to the interior of the home except in controlled amounts. A controlled indoor environment is both healthy and comfortable. Humidity can be controlled more easily in a SIP home resulting in a home that is more comfortable for occupants and less prone to mold growth and dust mites.
R-values for SIPs depend on the thickness of the SIP. See our R-value comparison for the minimum R-values by SIP size. Static R-values, like those included in the chart, rate the effectiveness of insulating material. However, they do not accurately describe how products perform in a real world setting. When fiberglass or other types of insulation are installed, they are installed around structural members made of wood or metal which have a very poor insulating value. Field-installed insulation materials are also prone to installation imperfections. The Department of Energy’s Oak Ridge National Laboratory has studied and tested the performance of entire wall assemblies in large sections. The resulting whole-wall R-value data reveals that a 4.5” SIP wall rated at R-14 outperformed a 2”x6” wall with R-19 fiberglass insulation.
We would be happy to answer any questions you have in the design phase. The construction of a SIP home or commercial building begins with the construction documents. Once the construction documents are in our hands, they are converted to SIP shop drawings that give the dimensions of each individual panel needed to complete the job. A work order and contract are generated and sent with the shop drawings to the builder, the building owner, and other involved parties for review. Once the work order and contract are finalized, the SIPs are fabricated and shipped to the jobsite for installation.
Builders can save money through decreased construction and labor costs. A recent study conducted by the R.S. Means unit of Reed Construction Data shows that building with SIPs can reduce framing labor needs by as much as 55% over conventional wood framing. The superior whole wall R-values and building tightness capable with SIPs allow HVAC equipment to be downsized and ductwork to be minimized. Builders can also significantly reduce jobsite waste disposal and temporary heat during construction. Homeowners that incorporate other energy efficient features with SIP construction can benefit from the energy efficiency of a SIP home with reductions in heating and cooling costs of 50% or more possible, may qualify for energy-efficient mortgages, and enjoy higher appraised values.
See our Products and Pricing page. When comparing prices, remember that the material price does not reflect the other things in labor, lifetime energy costs, HVAC systems. When all these factors are considered, building with SIPs is usually less expensive than other building systems.
For most applications, SIPs are structurally self-sufficient. The structural characteristics of SIPs are similar to that of a steel I-Beam. The OSB skins act as the flange of the I-beam, while the rigid foam core provides the web. This design is extremely strong and eliminates the need for additional framing. In cases where a point load from a beam or header requires additional support, a double dimensional lumber spline is field-installed at in-plane panel connections. SIPs are also used as curtain walls for steel frame or timber frame structures. In large commercial applications SIPs can minimize the amount of structural support needed and reduce material costs. In roof applications, SIPs can span long distances, allowing a minimal amount of structural supports to be used. Where needed, SIPs can rely on beams and purlins for support.
The majority of construction with SIPs is very similar to conventional framing. SIPs accept dimensional lumber and are fastened together using staples, nails, or screws. Proper sealing is especially crucial in a SIP structure. All joints need to be sealed with specially designed SIP sealing mastic or low expanding foam sealant, and/or SIP tape. Voids between panels and unused electrical chases need to be filled with low expanding foam. In addition to sealing, planning and consideration needs to be applied to material handling. Although smaller 4' × 8' panels can be set by hand, larger 8' × 24' panels require the use of equipment to unload and set.
The sound resistance of a SIP wall depends on the thickness of the gypsum drywall applied, the exterior finish applied, and the thickness of the insulating foam core that is used. SIPs are especially effective at blocking high frequency noise, and most homeowners notice the quiet comfort of a SIP home.
The high insulating properties of SIPs allow smaller HVAC equipment to be used. When working with an HVAC contractor, make sure their calculations take into account an accurate estimation of the typically low levels of air infiltration in a SIP home. Proper HVAC sizing is crucial because an oversized HVAC system will fail to reach the steady operating rate the equipment was designed for. Short cycling HVAC equipment will be less energy efficient and require more maintenance than properly sized HVAC equipment.
SIP buildings are extremely airtight and require mechanical ventilation. Ventilation systems bring fresh air into the building in controlled amounts and exhaust moisture-laden and stale air to the outside. By limiting air exchange to controlled ventilation systems, SIP homes allow for all incoming air to be filtered for allergens and dehumidified, amounting to better indoor air quality. Proper ventilation is important in all homes to preserve indoor air quality.
SIPs are compatible with other building systems. Wall panels can sit on a variety of foundation materials, including poured concrete, blocks, or insulated concrete forms. SIPs are sized to accept dimensional lumber and are seamlessly compatible with stick framing. Builders may choose to build with SIP walls and a conventional truss roof, or stick walls and a SIP roof with little difficulty. SIPs are also popular as a method of providing a well-insulated building envelope for timber frame structures.
SIP homes go up faster than traditionally framed buildings. A properly trained SIP installation crew can save a significant amount of time in a build cycle1. ACME Panels can be manufactured as big as 4' × 16', so walls can be assembled and put up quickly, reducing dry-in time. SIPs can be supplied as ready-to-install building components when they arrive at the jobsite, eliminating the time needed to perform the individual jobsite operations of framing, insulating, and sheathing stick-framed walls. Window openings may be precut in the panels, and depending on the size, a separate header may not need to be installed. Electrical chases are typically provided in the core of panels, so there is no need to drill through studs for wiring.
1 Edminster, Ann and Yassa, Sami. Efficient Wood Use in Residential Construction: A Practical Guild to Saving Wood, Money, and Forests. Natural Resource Defense Council, 1998.
Air barriers or vapor barriers are not required in SIP buildings because properly sealed SIPs create a code-compliant air barrier with a permeability rating of less than 1.0 perm. In addition, the foam core of SIPs is solid and continuous throughout the wall, eliminating the convection and condensation issues that can occur in cavity walls.
For construction professionals competent in standard wood framing techniques, the task of learning SIPs is not difficult. We offer onsite technical assistance for builders that are new to SIP construction who can talk to our SIP and construction experts.
On-site modification can easily be done using a few additional SIP-specific tools. Panels can be cut using a beam saw or a beam cutting attachment to a circular saw. The foam core can then be recessed for splines or dimensional lumber using a hot wire foam scoop or specialized angle grinder attachment.
Electrical wires are pulled through pre-cut channels inside the core of the panels called “chases.” We cut chases during the manufacturing process according to the electrical design of the home. Electricians can then use fish tape to feed wires through panel chases without compressing the insulation or having to drill through studs. Wiring can also be run through baseboard raceways and in the cavity behind the beveled spacer on SIP roof-to-wall connections.
As with conventional framing, plumbing should not be located in exterior SIP walls because of the possibility of condensation or supply lines freezing in cold climates. During the design phase of the project, all plumbing should be relocated to interior walls. If plumbing must be located on an exterior wall, it is recommended that a surface chase be installed on the interior of the wall to conceal plumbing. Plumbing penetrations such as DWV can be placed through SIPs if they are thoroughly sealed to prevent air infiltration.
Builders should consult the siding manufacturer's installation instructions for how to attach their product to SIPs. Because SIPs use very little solid lumber, an increased fastener schedule is often required when attaching exterior cladding. If the siding manufacturer does not offer recommendations for attaching their product to SIPs, a licensed architect or engineer can calculate the appropriate fastener frequency by obtaining fastener pullout capacities from us. It is also important that proper moisture management procedures be followed when applying any type of cladding to SIPs. The Builder's Guide to Structural Insulated Panels provides details for attaching various types of cladding materials. With the exception of metal and vinyl siding, the Builder's Guide recommends that all claddings be installed with a drainage gap between the cladding and the weather-resistant barrier in climates that average more than 20 inches of annual rainfall.
Recessed lights should never be embedded in structural insulated panels. To install recessed lights, an interior soffit must be constructed.
Cabinets are attached to SIPs all the time. It is, however, recommended that the cabinet manufacturer provide instructions on how to attach their product to SIPs. typically, an increased fastener schedule is required. Another option is to install plywood strips behind the cabinets to provide additional holding strength for fasteners. If the cabinet manufacturer does not offer recommendations for attaching their product to SIPs, a licensed architect or engineer can calculate the appropriate fastener frequency.
Some roofing manufacturers warranty asphalt shingles over unvented SIP roofs, while others void their warranty because of higher shingle temperatures. Research conducted by Building Science Corporation reveals that although asphalt shingle temperatures increase slightly (2° - 3° F) in an unvented roof assembly, the color of the shingles and the roof orientation have a much more profound impact on the durability of shingles. According to the Builder’s Guide to Structural Insulated Panels (SIPs) published by Building Science Corporation, the typical reduction of shingle life over an unvented SIP roof assembly is between one and two years. Builders seeking to comply with roofing manufacturer warranties can choose from a variety of more durable, non-asphalt roofing materials or provide a venting space between the SIP roof panels and the roofing material (known as a cold roof).
The area inside a SIP building envelope is considered conditioned space and will be ventilated by the building's HVAC system. There is no need to provide a vented attic beneath a SIP roof, and doing so would compromise the conditioned space of the building. Research conducted by Building Science Corporation on test homes in hot climates demonstrates that including the attic in the conditioned space allowed for more energy-efficient space conditioning and less probability of moisture-related issues (Rudd, Armin and Joseph Lstiburek, Vented and Sealed Attics in Hot Climates. Building Science Press, 1998). Some building science experts, such as Building Science Corporation Principal Joe Lstiburek, have advocated venting the roof by providing an air space between the SIP roof panels and the roofing material (known as a "cold roof"). This practice is not a requirement for SIP buildings, but an extra measure to improve the durability and moisture resistance of the building.