Column: Stick framing versus Structural Integrated Panel construction
Structural Integrated Panels are similar to ICF walls. They have a layer of foam insulation – usually closed-cell spray foam sandwiched between two layers of OSB (oriented strand board) or plywood sheathing. Bonding the foam to the outer panels creates a strong assembly, not unlike that of an I-beam. Panels are highly resistant to racking and shear loads and can withstand high winds and seismic activity. SIPs are typically known for good structural integrity, moisture and temperature control and higher insulating properties.
Building with SIPs presents several advantages over conventional framing methods, including increased energy efficiency, reduced possibilities of structural damage and deterioration over time, and reduced costs. SIPs save energy by reducing the heat loss characteristic of conventional wood framing, as well as by reducing air leaks. According to the Department of Energy, homes and commercial buildings constructed with SIP walls save 25 percent in energy loss, and when floors and roofs are constructed using SIPs, savings increase exponentially.
Despite these advantages, sticker shock may be a deterrent to using SIPs. However, according to a study by Reed Construction, while the initial cost of SIP is typically 2 percent to 5 percent higher than conventional building materials, when combined with waste reduction, increased site productivity, and reduced framing costs the overall cost is considered virtually the same.
However, as with ICFs, it is wise to use contractors who have measurable experience in the use of these products. Too many builders find SIPs to be unfamiliar and refuse to work with them because special tools and often cranes are required for installation. Careful project planning and sufficient lead time is also required to accommodate special engineering, code approvals, manufacturing and shipping of the product. However, most panel producers provide engineering services and drawings to help facilitate the approval process.
Panels are made in a factory and trucked to the construction site ready for installation. With the help of a crane, wall sections can be assembled quickly. The insulation in them is only interrupted at the relatively infrequent seams so thermal bridging is much lower than in a similarly shaped stud wall Key Materials.
Unlike conventionally framed walls, SIPs have no wall cavities and therefore fewer opportunities for energy losses due to internal convection. Continuous insulation means that SIP houses have much less air infiltration than standard framed houses, as air infiltration, is responsible for as much as 40 percent of heat or cooling loss in the average home.
Manufacturer specifications for sealing SIP seams vary, but most systems require caulk, adhesive or spray foam between panels. In addition to spray foam, some builders seal all seams from the interior with peel-and-stick butyl tape. If a SIP home is being built to meet Energy Star requirements, air sealing between panels must be sealed with expanding foam, and manufacturer-approved sealing mastic or tape.
As an example, in a comparative test conducted by Oak Ridge National Laboratories researchers built two identical 2,600 sq. ft. homes, one made of SIPs and one with conventional wood framing and fiberglass insulation. The SIP research home was five times more airtight than the wood-frame home when measured by a blower door test.
The lifespan of SIPs is 50 years or more and the air-tight construction of SIPs virtually eliminates the possibility of mold. SIPs also eliminate the need to find studs prior to the installation of siding or drywall. You shouldn’t leave SIPs exposed to the elements for long periods, especially if they’re made from OSB or plywood. If moisture gets in them, the entire structure can be compromised. Once the panels are up and in place, house wrap should go up quickly to prevent moisture from getting in.
As with any building, those constructed using SIPs can become susceptible to rodents and insects. The DOE suggests applying insecticides to panels, maintaining indoor humidity levels below 50 percent, and treating the surrounding ground with insecticides before and after construction to help reduce the risk of an insect or rodent invasion. As with all wooden framing fire is a concern; however, covering SIPs with an internal material such as gypsum and applying concrete siding externally reduces the risk of fire for homes in wooded areas.
SIP construction is more expensive than standard frame construction, but because the resulting building envelope is tighter and insulation values higher, using them makes it possible to downsize heating and cooling equipment, and lower operating costs over the life of the building.
In my LEED gold home, I used ICFs for the basement and crawl space and SIPs for the main walls. The result was a very well insulated home with a good price performance combination between the two technologies.
For more information, contact Paul Scrivens at www.greenhomeenergyadvisors.