SIPs Structural Insulated Panels FAQ

Q: What is a SIP?

A: SIPs (Structural Insulated Panels) are a type of composite building material that are used to define the structure of a building, much like an I-beam or I-column. Most SIPs are made of a layer of a foam core (which provides insulation) that is laminated between two layers of wood sheathing (which provide the structure). The panels can be made from metal, drywall, plastic, cement or, most commonly, OSB (orient strand board). Although they are most commonly used in walls, SIPs can also be used in floors, ceilings and foundations.

Q: Are SIPs strong? How do they compare to traditional structural elements?

A: The way that materials inside a SIP are sandwiched make it quite strong. In fact, SIPs act like I-beams in how they resist both vertical compressive forces and horizontal buckling forces, and some tests have shown that SIPs can range from 2 to 7 times stronger than traditional framing. Some SIPs may also use integral studs as splines to help carry structural load.

Q: How valid are claims of SIP energy efficiency?

A: In general, claims about the high efficiency of SIPs are reliable, and homes made with SIPs tend to be very energy efficient. This is because:

  • Foam provides better insulation than traditional fiberglass insulation.
  • Less wood framing in SIPs generally results in higher R-values.
  • The continuous foam in SIPs typically has fewer flaws than traditional batt installations.
  • Foam doesn’t allow air infiltration.

Q: Does foam lose R-value as it ages?

A: The aged R-value of a SIP is its long-term R-value. The most common type of foam used in SIPs is expanded polystyrene insulation (EPS). EPS typically has a lower aged R-value (about R-4 per inch), and it maintains its R-value once it is in place. Urethane foam, on the other hand, stabilizes at a higher R-value (about R-7 per inch), and once it is fully cured it has an R-value that is about twice that of a fiberglass wall.

Q: Are SIPs bad for indoor health?

A: No. While some people may worry that a home built with SIPs will be too “tight,” (meaning that it is too insulated and the house does not have enough natural ventilation or room to “breathe”), that’s not the case. In general, it’s smarter to build a tight home that allows you to  intentionally control air movement and ventilation, instead of building a leaky home and then trying to control airflow after the fact.

Q: Can SIPs be used to build passive solar homes?

A: Yes. With the right geographic location and complementary architectural elements, SIPS can be used in passive solar home designs. In fact, some studies show that with the right conditions, SIP building shells and solar work very well together.

Q: Do SIPs meet building codes?

A: Because building codes differ from place to place, many SIP manufacturers list their panels and products with regional code authorities. This makes it easier for their products to be accepted for use by local code officials. Not all building officials are familiar with SIPs, but many are becoming so with wider use of the product. To see if SIPs are authorized for use in your community, you or your builder should check with your local building department.

Q: Is wiring a problem in SIP homes?

A: Typically, no. Although wiring a home with SIP panels takes extra planning during the pre-construction phase, panels often come with pre-cored channels (called “chases”) that allow wire to be inserted through the cores without damaging the structural integrity of the panels. Then, when panels are placed, minor cuts and adjustments are made to accommodate switch boxes and other electrical elements (as necessary).

Q: Are there performance problems with SIPs in fires?

A: SIPs are flammable, but not any more so than a typical stick-framed dwelling.  According to the Structural Insulated Panel Association, SIPs present a “manageable” risk of fire. Since residential and commercial building codes will typically require an application of a fire-resistant thermal barrier, properly treated SIPs can provide a surprising level of fire resistance.

Q: Are insect infestations from ants and termites a problem with SIPs?

A: Unfortunately, termites and ants can infiltrate SIPs. Although they are no more likely to infest a SIP home than they are a traditional stick-framed home (especially since insects do not eat the foam for food), pests have been known to tunnel out foam and nest inside panels. Preventative treatments (such as borate-treated foams, topical sprays, and physical barriers) are available to deter infestation.

Q: Are SIPs green?

A: There are several environmental benefits to using SIPs. For instance, SIP homes do not need nearly as much framing, they offer considerable heating and cooling savings, and there is less “tree waste” when using SIPs than using solid lumber. The beads used to make the polystyrene foam are a natural by-product of the refinery process that would otherwise go to waste.  The beads expand to over 100 times their size with heat and moisture to create the foam blocks. Also, because SIPs are pre-cut at the factory, there is less waste produced at job sites (which means less landfill waste).

Q: Do SIPs cost more than frame walls?

A: Typically, SIP walls cost a little more than frame walls because the materials cost quite a bit more. This, however, can be offset by lower labor costs if builders plan and design to optimize their SIP usage. For instance, designing homes with two-foot and four-foot increments, pitching roof SIPs in particular ways, and other adjustments can all reduce SIP costs.

Q: Are SIPs perfect and foolproof?

A: No, and nothing is. As with any manufactured product, SIP manufacturing requires stringent quality control methods at the factory to ensure a quality product. If you’re a homeowner considering using SIPs for your home, be sure to ask about the manufacturer’s QC (“quality control”) process. In addition, you will want to make sure that you work with an architectural designer and builder with on-site personnel who know how to properly use SIPs to meet structural loads and how to properly assemble panels so that they seal out air and water.

Q: Should I use SIPs for my home? Are SIP houses better?

A: That depends on your needs and budget. Assuming the SIPs used in your house are properly designed, properly manufactured and properly installed, a SIP house will typically be more energy-efficient and stronger than a traditionally framed home. The key is to make sure that you are working with high-quality products and experienced professionals who truly know how to best utilize the product.

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