Frequently Asked Questions Regarding Structural Insulated Panels (SIPs)
Structural insulated panels (SIPs) are high performance building panels used in floors, walls, and roofs for residential and light commercial buildings. The panels are made by sandwiching a core of rigid foam plastic insulation between two structural skins of oriented strand board (OSB), or plywood. Plywood thickness may increase with larger buildings. 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. Building with SIPs will save you time, money, and labor.
SIP buildings go up significantly faster than traditionally framed structures. A properly trained SIP installation crew can save a significant amount of time in a build cycle. Panels can be manufactured as big as 8’x24’, so entire walls can be put up quickly. SIPs can be supplied as ready to install building components when they arrive at the jobsite, eliminating the time needed to perform individual jobsite operations of framing, insulation, and sheathing as in stick-framed walls. Window openings are precut in the panels, and depending on the size, a separate header may not need to be installed. Electrical chases are provided in the core of panels, so there is no need to drill through studs for wiring. SIPs are capable of reducing dry-in time, meaning interior and subcontractor work can begin earlier.
Because SIPs are structurally sufficient, the amount of additional framing required is minimal. SIPs are always straight and true, there are far fewer callbacks, no culling studs, or need to straighten walls. SIPs also provide a uniform nailing surface for both interior and exterior finishing.
The superior whole wall R-values and building tightness of SIPs allow HVAC equipment to be downsized and ductwork to be minimized. When combined with other energy efficient technologies, SIPs can cut annual heating and cooling costs by 50 percent or more. Homeowners have the opportunity to apply for Energy Efficient Mortgages and enjoy the higher appraised value of an energy efficient building.
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 reduced. 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 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. Detailed information on the structural performance of SIPs is available.
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 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. Ventilation systems can be designed to incorporate heat recovery ventilators (HRV’s). These advanced systems harness heat being exhausted from the home and utilize it to heat the fresh air coming into the home for an even more efficient use of energy. Proper ventilation is important in all homes to preserve indoor air quality.
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. Ventilation systems can be used to filter potential allergens from entering the home. 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.
Residential building code typically requires building materials to have at least 15 minutes of fire resistance. Structural insulated panels faced with 0.5” gypsum drywall that have a system listing to NFPA 286 or ASTM E119 by a registered certification agency meet this requirement. Many SIPs carry this certification. Drywall must be attached per manufacturer specifications to meet this requirement. Commercial builders may need a one hour fire rated wall, which is achieved by testing and listing to ASTM E119 by a registered certification agency. Many SIPs carry this certification. Two hour rated systems are also available.
As a general rule, all panels need to be supported from below. SIP walls must have both OSB skins in contact with the foundation to be effective. Roof panels need to be supported from underneath via ridge beams, rafters, purlins, or load bearing walls. Point loads from beams or purlins need to rest on dimensional lumber splines at joints between panels. Panels are joined with manufactured splines, specially designed panel screws, and dimensional lumber. SIPs arrive at the jobsite with construction details showing these connections.
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 tremendously popular as a method of providing a well-insulated building envelope for timber frame structures.
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. Voids between panels and unused electrical chases need to be filled with low expanding foam. Roof joints can be sealed on the interior with specially made SIP tape. In addition to sealing, planning and consideration needs to be applied to material handling. Although smaller 8’x 4’ panels can be set by hand, larger 8’x 24’ panels weigh up to 700 lbs and require the use of a fork lift with 6’ forks to unload at the site. A boom truck or a crane is used to set large panels on the roof.
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.
Electrical wires are pulled through precut channels inside the core of the panels called “chases.” Manufacturers 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. Chases can easily be added to panel after installation if necessary by cutting access holes in the panels. Wiring can also be run through baseboard raceways and in the cavity behind the beveled spacer on SIP roof-to-wall connections.
EPS panels are treated with an effective, non-toxic additive that will deter insects. The additive is environmentally sound and contains no dyes, formaldehyde or ozone-depleting HCFC’s. The additive is inert, non-nutritive, highly stable and therefore will not decompose, decay or produce undesirable gases or leachates. The insect-resistant foam panels are recyclable and safe for waste-to-energy systems and landfills. The treatment is a process which uses a natural mineral formulated to resist normally occurring exposure to woodboring insects, specifically carpenter ants and termites. The non-toxic treatment is EPA Registered, meets the standards of ASTM D3345 and WPA EL 12-72, and lasts as long as the rigid insulation.
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.
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 because doing so would compromise the conditioned space of the building by allowing open ventilation with unconditioned space. Most roofing manufacturers specify how to attach their product to SIPs. Please contact roofing manufacturer for application instructions. As with any roof, a complete drainage plane needs to be installed between the SIP and the roofing material.