| FREQUENTLY ASKED QUESTIONS ABOUT STRUCTURAL INSULATED PANELS (SIP) |
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What are Structural Insulated Panels?
Structural Insulated Panels are building panels which integrate structure and rigid foam insulation for the construction of walls and roofs of residential and light commercial buildings. The panels are typically made by sandwiching a core of rigid foam insulation between two structural skins of oriented strand board (OSB). 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. |
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How does the SIP panel design and fabrication process work?
The construction of a SIP home or commercial building begins with the construction documents. Once the construction documents are in the hands of a SIP manufacturer, dealer/distributor, or design professional, they are converted to SIP shop drawings that give the dimensions of each individual panel. |
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What are the R-value of SIPs?
R-value can vary depending on type and thickness of rigid foam insulation. Two types of foam commonly used are expanded polystyrene (R-4/inch) and polyurethane (R-7/inch). Common thicknesses range from 4 1/2” - 12 1/4”. |
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Does the insulation lose R-value over time?
Rigid foams used in SIPs are factory installed and have a stable R-value that will not deteriorate. Whereas blown in or batt insulation can settle or move over time decreasing the overall R-value. |
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What is a thermal barrier?
A thermal barrier occurs wherever there is a layer of insulating material separating the interior space of a building from the outside. In a SIP building the entire building envelop is a thermal barrier. Whereas with conventional stick framing 20% of the envelop has no thermal barrier due to structural components like studs and trusses. |
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How much faster can I build with SIPs?
Panels can be manufactured as big as 8- by 24-ft., so entire walls can be 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 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. |
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How sustainable are SIPs?
A SIP building envelope provides high levels of insulation and is extremely airtight, meaning the amount of natural resources used to heat and cool the home are drastically reduced.
Resource Use: 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.
Waste Minimization: Since SIPs are prefabricated in the factory, there is less jobsite waste that needs to be landfilled. Factory fabrication is often done using optimization software and many manufacturers recycle factory scrap to make other foam products.
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How strong are SIPs?
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. |
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How important is ventilation?
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. HRV (Heat Recovery Ventilators) are ideally suited to SIP building by providing fresh air that is within 80% of interior air. |
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How do structural insulated panels react to fire?
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 1/2” gypsum drywall meet this requirement. |
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What is the learning curve for structural insulated panel installation?
For construction professionals competent in standard wood framing techniques, the task of learning SIPs is not difficult. Many SIP manufacturers and dealer/distributors offer onsite technical assistance for builders that are new to SIP construction. |
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What considerations do you need to take into account when building with structural insulated panels vs. conventional framing?
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 8- by 4-ft. panels can be set by hand, larger 8- by 24-ft. panels require the use of equipment to unload and set. |
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Can structural insulated panels be modified on site?
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 to recess the core. |
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How are electrical wiring and fixtures installed?
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. Wiring can also be run through baseboard raceways and in the cavity behind the beveled spacer on SIP roof-to-wall connections. |
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Can recessed lights be used in structural insulated panels?
Recessed lights should never be embedded in structural insulated panels. To install recessed lights, an interior soffit must be constructed. |
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Are structural insulated panels susceptible to mold and mildew?
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. |
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Does a building with a structural insulated panel roof need to be ventilated?
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. Most roofing manufacturers specify how to attach their product to SIPs. |
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What style of houses can be built with SIPs?
SIPs structural flexibility far surpasses conventional framing. Which allows many styles of homes to be built in many environments. |
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Are SIPs suitable to build a Passivhaus?
Yes. The insulating and air sealing capabilities of SIPs makes it the best choice for walls and roofs of a Passivhaus. |
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