How Structural Insulated Panels Work

With so many pieces to be assembled, it's easy to see why stud frame houses can take lots of time and labor to build.
With so many pieces to be assembled, it's easy to see why stud frame houses can take lots of time and labor to build.
Pete Saloutos/UpperCut Images/Getty Images

­If you've ever seen a typical house being built, at one stage in the process you probably saw a wooden latticework of spindly 2x4s outlining a shape somewhat reminiscent of a whale's ribcage. But although this method is currently the standard, there are other ways to build a home -- and some of them can save you quite a bit of money in ­the long run.

One of these alternate techniques is to construct a house using SIPs, which stands for structural insulated panels. SIPs are prefabricated solid sheets of building material that are generally constructed of a foam core surrounded on each side by a layer of oriented strand board (OSB). They're most commonly used for walls and roofs, but can also serve as floors and foundations.

The idea behind structural insulated panels was first conceived of in the 1930s, but the invention really took shape in 1952 with the creation of the first foam-filled SIP [source: SIPA]. The advent of CAD/CAM technology and CNC machining further energized the process. Using CAD (computer aided design) and CAM (computer aided manufacturing) software means the blueprints for an SIP house can be converted into detailed instructions for a CNC (computerized numerical control) machine. Then it can quickly and accurately whip out the exact components needed. This made the process more efficient and streamlined, minimizing waste and reducing cost.

­You might be wondering at this point: If SIPs were such a hot new idea, how come stick frame houses are st­ill popping up like weeds? The answer, in a nutshell, is that building trends often shift at a glacial pace. SIPs met with success in the 1970s during the energy crisis, but as that faded away, so did much of the popularity of building energy-efficient homes. Since energy issues are just one of the many concerns touching today's markets, SIPs and similar building prospects are waiting in the wings, ready to make a big comeback.

We'll get into the hows and the whys in a second, but first we'll take a look at some of the different materials that can be used to make SIPs on the next page.

Making the Magic Happen: Inside a Structural Insulated Panel

Architectural blueprints can be digitally created to provide instructions for manufacturers to cut prefab SIPs.
Architectural blueprints can be digitally created to provide instructions for manufacturers to cut prefab SIPs.
Vasko Miokovic/iStockphoto

­Ready to crack a panel open and see what makes it tick? The core of an SIP panel is usually created out of foam (sort of like the creamy goodness inside an Oreo cookie) and is most frequently made of expanded polystyrene (EPS) foam board [source: U.S. Department of Energy]. Other common materials are polyurethane and polyisocyanurate, which tend to be mo­re expensive but offer greater insulation, provide a better moisture barrier and are more resistant to fire. The core can alternatively be comprised of other elements like compressed straw, which is more environmentally friendly and renewable but also heavier and less insulating.

If you've stopped to consider a home's electrical system, you might be scratching your head right about now. If the walls are solid panels, are the wires strung up around the house like Christmas lights? Not quite. During manufacturing, narrow channels typically known as chases or wirechases are either formed directly into the foam or tunneled out later. Wires can be strung through these conduits and along other inlaid niches.

As we read on the last page, oriented strand board made from fast-growing trees is commonly used as a structural skin, although plywood, fiberglass and cementboard are among the other options. Something else to note: During construction, siding and roofing aren't the only components that'll be flushing out the look of your SIPs. Gypsum board and other fire-rated materials are usually applied on the inside to help slow a blaze in the event of a house fire.

In the production process, the two sections of sheathing and the foam core are sandwiched together and cut to the proper size specifications. These can be standard dimensions or kits customized for a particular job. Manufacturers might cut window and door openings, or leave that to the construction crew. The panels are sometimes labeled for easy assembly -- sort of a paint-by-number setup -- and then they're ready to be shipped to the site.

Although there are industry standards, SIPs are highly customizable in shape, density, size, thickness and appearance. They can be used for residential homes as well as light commercial buildings. On the next page, we'll find out how SIP projects are assembled and some of the advantages they offer.

Raise the Roof: Building with SIPs

SIPs are fitted together like a jigsaw puzzle.
SIPs are fitted together like a jigsaw puzzle.
Bart Coenders/iStockphoto

­Unlike stud frame houses, which are usually constructed completely on-site, houses using SIPs tend to be mostly prefabricated. As we read about on the last page, structural insulated panels are made by manufacturers and shipped out to construction sites, where each wall goes up whole. This means that even though a new homeowner is likely to be shelling out some extra cash on materials, he or she ­will probably be saving money on labor costs and jobsite waste. One thing homeowners shouldn't skimp on is experience. While SIP houses aren't as perplexing to figure out as a Rubik's cube, they can present a challenge for someone attempting to build one for the first time -- maybe more along the lines of one of those monochromatic jigsaw puzzles. Having someone with a little know-how can make everything go much smoother.

The main goal while building an SIP house is to make it as airtight as possible, which helps the insulation work to its maximum capacity. As the panels are lifted into place -- often with the use of a crane or a forklift -- they're joined together carefully. This is typically accomplished with a variety of items like expanding foam, sealing tape, sealing mastic and good, old-fashioned nails. The important thing to remember is that if the house is going to come out right, the manufacturer's directions must be followed to the letter. Yet even despite that, it may be necessary to complete some small on-site modifications to the prefab sections (another reason having a pro can be an asset), but with the right tools, a quick fix can be done in a snap.

The other tricky elements to keep in mind are wind and water -- or ventilation and moisture to be more precise. Because the goal is to seal SIP homes into tight envelopes (not like drafty stick frame homes with constant gaps between insulation) they need to be built with care. For example, you'll need to select a ventilation system (typically one that can exchange heat between stale outgoing air and fresh new air) which is a suitable size for the building's needs. SIPs are more energy-efficient, so they don't need the heavy-duty HVACs of other buildings. Smaller units can run on less power for longer lengths of time -- and they dehumidify in the process, which is key to keeping mold worries off your mind. Another way this comes into play is between the siding, roof shingles and outer shell of the SIPs. Here too, ventilation and moisture can be a problem unless the panels are given adequate space to breathe and drain.

But once the house is finished and the moving van pulls to a stop at the curb, it's time for the kudos to start rolling in. On the next page, we'll examine what kind of return an owner can get from an SIP home and how the panels can be beneficial for people looking to take the plunge into prefab.

SIP Specifics

At this point you're probably dying with curiosity, eager to find out what all the fuss is about. Well, although SIP homes aren't foolproof pictures of perfection, there are a number of benefits to building this way.

  • Materials: EPS (the foam most commonly found inside our SIP ice cream sandwich) is cheap, available, tough, easy to produce and easy to work with. The oft-used OSB outer skins come from replenishable, quick-growing softwood trees, and­ SIP components are recyclable.
  • Efficiency: Buildings built with SIPs have greater thermal capabilities and less insulation breaks for heat to escape. They offer more uniform temperatures while decreasing the heating and cooling load. Plus, because they require smaller HVAC systems, they also decrease the amount of greenhouse gasses grabbing at your conscience.
  • Simple Perks: SIP homes tend to be quieter -- the panels provide a better sound barrier than stick-frame houses -- and they tend to be healthier. As long as proper ventilation and filtration are maintained, the house can preserve better indoor air quality, leaving dust, mold and allergens at the door. And this one may sound silly, but you'll appreciate it if you've ever tried to hang something heavy up on the wall -- only to end up watching your mistakes quickly morph it into the crime scene for a shootout. There's no need to locate studs; the whole wall can handle the load.
  • Strength: This brings us to the sturdiness of SIP-built buildings. Instead of having the weight of the structure centered on the frame studs, the entire shell is able to shoulder the load. These homes also tend to do better during natural disasters like hurricanes and earthquakes -- although this is in no way a guarantee that the house will weather the storm.
  • Industry: SIPs are starting to turn more heads in the building industry, although the demand for them is still largely consumer-based. But even reluctant builders have a few benefits waiting for them if only they'd sign on. SIPs can help deal with labor shortage issues and extend the building season. If the insulating shell can be whipped up in a few days, construction workers can spend the rest of the winter nice and warm while they work on the interior.
  • Bottom Line: Now let's get down to the brass tacks. SIP homes generally cost more to build than stud frame homes, but they work hard to earn their keep. Besides the money saved during construction (remember the prefab savings, the decreased labor cost, the lack of materials waste and the smaller HVAC), they also offer long-term savings. Besides reductions on utility bills, SIP homeowners may be eligible for tax breaks and energy-efficient mortgages (also known as EEMs), which come with a number of financial perks. Worried about moving and losing your investment? SIP homes tend to bring home the bacon as far as resale values are concerned.

So if you're looking to go prefab in your next dwelling, with good research and planning, a SIP home can be the coziest home sweet home you've ever had. It's important to ensure you have a trusted and experienced professional heading the work, and a little product support from the manufacturer is a plus. On the next page, you can get more information about home construction and how to jump into a project of your own.

Related HowStuffWorks Articles

More Great Links

Sources

  • "About Structural Insulated Panels." Cozy Living Homes. (12/11/2008) http://www.cozylivinghomes.com/sips/index.html
  • APA -- The Engineered Wood Association Web site. (12/10/2008) http://www.apawood.org/
  • CAD/CAM/CNC Glossary of Terms. MicroSystemsGeorgia. 5/8/2008. (12/11/2008) http://www.microsystemsgeorgia.com/cnc.htm
  • Structural Insulated Panel Association Web site. (12/10/2008) http://www.sips.org/
  • "Structural Insulated Panels." U.S. Department of Energy's Consumer Guide to Energy Efficiency and Renewable Energy. (12/10/2008) http://apps1.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic=11740
  • "Foam Board." U.S. Department of Energy's Consumer Guide to Energy Efficiency and Renewable Energy. (12/10/2008) http://apps1.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic=11620?print
  • McNair, Dave. "On Architecture - Retrofit: Are SIPs the New Way to Build?" The Hook. 3/30/2006. http://www.readthehook.com/Stories/2006/03/30/onarchretro.aspx
  • Miller, Stephanie. "Construction Products Review: Structural Insulated Panels." Architects Online. 8/24/2006. (12/10/2008) http://www.architectmagazine.com/industry-news.asp?articleID=353470&sectionID=1022&refresh=true
  • Ross, John. "SIPs: Are They Right for Your Next Project." Fine Homebuilding. 2007. (12/11/2008) http://www.pbssips.com/Newsroom/Fine%20Homebuilding%206-07.pdf
  • "Structural Insulated Panels." APA -- The Engineered Wood Association Web site. 12/2007. (12/10/2008) http://www.apawood.org/pdfs/managed/H650.pdf?CFID=9315615&CFTOKEN=34236811