Frequently Asked SIPs Questions

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 very important when assembling SIPs. All joints need to be sealed with specially designed SIP sealant or expanding foam sealant, and in some cases self-adhesive SIP tape. SIPs also require consideration of how panels will be staged and placed on the jobsite. Although smaller 8- by 4-foot panels can be set by hand, larger 8- by 24-foot panels require the use of equipment to unload and set.

SIPs are compatible with almost any building system. 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 enclosure for timber frame and steel structures. 

SIP construction is recognized by the International Code Council body of building codes, which are used by most jurisdictions in the U.S. SIPs are also approved by the State of Florida for High-Velocity Hurricane Zones (HVHZ). 

For residential buildings, specific construction practices for SIP wall systems are included in Section R610 of the 2018 International Residential Code. For applications beyond the scope of Section R610, the building inspector will typically require a licensed engineer or architect to approve the building plans prior to construction. An engineer’s approval is always required in high wind areas, high seismic zones, and commercial buildings. 

Onsite modification can easily be done using a few additional SIP-specific tools. Oversized 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. 

For most applications, SIPs are structurally self-sufficient. The structural characteristics of SIPs are similar to that of a steel I-beam. The OSB facers 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 or engineered wood 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 rely on beams and purlins for support. SIPs can span long distances, allowing a minimal amount of structural supports to be used. Embedding I-joists into the SIP roofs can also easily increase roof spans and loads. 

R-values for SIPs depend on the thickness of the SIP and the type of core material that is used. See SIPA’s R-value chart for the minimum R-values of commonly available SIPs.

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 that have 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-inch SIP wall rated at R-14 outperforms a 2 × 6 wall with R-19 fiberglass insulation.

A high-performance SIP building enclosure often allows smaller HVAC equipment to be specified. It is important to work with a qualified HVAC professional that can accurately estimate the low levels of air infiltration in a SIP home or commercial building. 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.

Electrical wires are pulled through pre-cut channels inside the core of the panels called “chases.” Chases are added during the manufacturing process according to the electrical design of the home. Electricians can feed wires through panel chases without compressing the insulation or drilling through studs.

SIP buildings are extremely airtight with air leakage rates well less than 3 air changes per hour at 50 Pascals of pressure (3.0 ACH50) 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, creating better indoor air quality. Proper ventilation is important in all homes to preserve indoor air quality.

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.

This should not be confused with the requirement for external water-resistant barriers that protect all external wood structures from bulk water. See the Builder's Guide to SIPs by Joseph Lstiburek for detailed recommendations on vapor barriers.

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 fastening 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 the SIP manufacturer.

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 (SIPs) 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.

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 degrees 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 or ventilated 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. 

Some building science experts recommend venting the roof by providing an air space between the SIP roof panels and the roofing material (known as a “cold roof”). Although this best practice is not a requirement for SIP buildings, it is a sensible extra measure to improve the durability and moisture resistance of the building. 

Recessed lights should never be embedded in structural insulated panels. To install recessed lights, an interior soffit must be constructed. Nowadays, more energy-efficient, modern, thin LED lights have replaced the need for recessed light fixtures.

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. Another option is to construct a small section of the wall using conventional wood framing that can be used to run plumbing. Plumbing penetrations such as drain water vents (DWV) can be placed through SIPs if they are thoroughly sealed to prevent air infiltration. 

It is 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. Due to the consistent, flat nature of SIP walls, cabinets typically hang easier with fewer fitting irregularities. 

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 by obtaining fastener pullout capacities from a SIP manufacturer.