Structural Insulated Panels - FAQs

SIPs or Structural Insulated Panels are high-performance building panels used for floors, walls, and roofs for residential, commercial, and agricultural projects. The panels are made by sandwiching a polystyrene foam core between two structural skins of oriented strand board (OSB), or plywood. The skin thickness may increase for larger buildings. EPS SIPs are manufactured under factory-controlled conditions and can be custom designed for each home. The result is a building system that is strong, energy-efficient, and cost-effective. Building with SIPs can save you time, money, and labor. 

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.

Energy efficiency
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 handling in plane compressive loads.

The high insulating properties of SIPs allow for 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. 

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, resulting in 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 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.

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.

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 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 a 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.

SIP buildings can go up significantly faster than traditionally framed structures when being erected by a properly trained SIP installation crew. This reduces dry-in time and allows interior and subcontractor work to begin earlier. EPS SIPs can be manufactured as large as 8' X 24'. SIPs can be supplied as ready-to-install building components when they arrive at the job site, eliminating the time needed to perform individual operations of framing, insulation, and sheathing. Window openings are pre-cut in the panels, and depending on the size, a separate header may or may not need to be installed. Electrical chases are provided in the core of the panels, so there is no need to drill through studs for wiring.