SIPs, Getting to the Core

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sip-panel_schematic.jpgStructural Insulated Panels (SIPS) are great energy savers in new construction, saving significant amounts in home energy use. Providing structure for walls, floors, ceilings and roofs, they go up quickly, saving labor costs, and provide a strong structure. Manufacturing of SIPs uses significantly less dimensional lumber and conserves timber resources. They create an airtight dwelling that is more comfortable and quieter than some other conventional forms of construction.

They are typically comprised of 2 sheets of OSB (oriented strand board) or plywood that sandwich a foam core, usually made of expanded polystyrene (EPS) or polyurethane. So, what’s the difference between the two types of foam?

  • R-Value: Polyurethane has far better R-Value
  • Density: Polyurethane is more dense and therefore is inherently stronger.
  • Bonding agent to outer skin: Polyurethane acts as the bonding agent, so no additional glue is needed as in use with polystyrene. Typically glue contains harmful VOCs that outgas.
  • Fire resistance: polystyrene (the disposable, white “coffee cup” material) is thermoplastic. When heated to high temperatures, as in a fire, thermoplastic materials will soften and melt (although polystyrene SIPs are more fire resistant than stick-frame construction). Polyurethane, on the other hand, will not ignite or melt.
  • The manufacturing of polyurethane produces HCFCs which harm the ozone layer, while polystyrene manufacture does not. Also, less energy is required to manufacture polystyrene than polyurethane. Polystyrene is also more recyclable.
  • Moisture resistance: because polyurethane has one of the lowest moisture permeability ratings, it is preferred over EPS in high humidity climates. EPS panels would warrant an extra moisture barrier.
  • Chemical resistance: polyurethane is resistant to most chemicals, where as polystyrene will react with chemicals like petroleum-based products.

Another, more environmentally-friendly option for SIP core is waste agricultural straw. Being a renewable resource and recyclable, it has its advantages. However, straw-core SIPs have a lower R-Value and are heavier than the other options, making the increased embodied energy a consideration.

Sources: and Ecology Action

Tag(s): Energy, Green Building


3 Responses to “SIPs, Getting to the Core”

  1. SP on March 6th, 2008 2:49 pm

    I agree in that SIPs are better then conventional building, but we need to figure out that core material. I love the idea of using straw, but I worry about pests (what better place for a mouse to live), fire resistance, and mold resistance.

    However, new foams are entering the market using bio based components instead of petroleum. I believe these products will be the future of SIP cores.

  2. joyceb on March 13th, 2008 11:56 am

    Pests are a problem with any house. Check out the U.S. Department of Energy’s “Areas of Concern” (near the end of the page)regarding SIPs here:

  3. Meredith on March 24th, 2008 9:30 am

    I agree with using a non-petroleum based core. Because this is a commodity it is hard to maintain a stable price structure. Also we would prefer bio-based such as soy, but the price is still too high for this to be affordable to the majority of the building industry and again, we’d be tied to the commodity pricing scale.

    We are continuiously working in R&D to perfect our SIP system and are actually interested in looking at new and improved products out there that would not be based on the commodities market such as petroleum, lumber, etc.

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