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Understanding SIPs : International edition : Tuesday, 12 December 2017 10:18 DT : a service of The Public Press
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A Building System Comes of Age

     by Lisa Ford and Gary Dennis

 

For years, while consumers muddled over the necessity for energy-efficient building systems, there was a sleeping giant in the building industry.

 

Now, after years of skyrocketing heating fuel prices in the U.S. and associated movements to conserve the same, the giant is awake. Structural insulated panels – SIPs, as they’re known to builders – are coming into their own and causing some who knew nothing more than conventional stick-framing to give the alternative building method a look.

 

But it’s new. It’s different. And that makes the general building public – homeowners, general contractors and even large commercial contracting firms alike – skittish.


 

For years, while consumers muddled over the necessity for energy-efficient building systems, there was a sleeping giant in the building industry.

Now, after years of skyrocketing heating fuel prices in the U.S. and associated movements to conserve the same, the giant is awake. Structural insulated panels – SIPs, as they’re known to builders – are coming into their own and causing some who knew nothing more than conventional stick-framing to give the alternative building method a look.

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But it’s new. It’s different. And that makes the general building public – homeowners, general contractors and even large commercial contracting firms alike – skittish.

But ultra-tight homes and potential heating cost savings of up to 50 percent decrease the "skittish" factor significantly. And that’s helping the SIP industry keep its head above water, even in a time of rock-bottom housing starts and shaky consumer confidence.
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SIPs Explained

SIPs are wall and roof systems that provide an exterior & interior sheathing of oriented strand board (OSB), and an insulating foam core all in one product. The foam cores come in three flavors: polyisocyanurate (urethane); expanded polystyrene (EPS); and extruded polystyrene (XPS).

Choosing an insulation is based on the desired R-value for a building envelope. R-value is the measurement used to determine the building’s ability to impede heat flow; the greater the R-value, the higher the resistance.

As for the foam core choices, EPS holds a lower R- value per inch, but the best price for performance. While XPS and urethane both offer higher R-values per inch, urethane has shown to lose its R-value over time and in some cases its structural capacity as well. Traditionally, EPS has held it’s own as the go-to foam core for many SIP shoppers, but XPS is quickly gaining popularity for customers who prefer thinner wall and roof profiles. .

While most in the SIP industry would agree the "standard" SIP includes two SIP-grade 7/16" OSB skins, it’s also well known that some manufacturers can mix and match. Requests for 5/8" plywood skins or drywall skins on the interior are common in the SIP world.

 

Applications

SIPs have the flexibility of being used for both structural and non-structural applications. They can be used to enclose timber frame or steel frame buildings where loads are being carried by the timber or steel. Here the panels are simply a thermal envelope attached to the frame.

SIPS gained popularity with the resurgence of timber framing in the 1970s. But in more recent years, SIPs have taken on a life of their own – homeowners, architects and builders are now using the panels without the support of a frame structure beneath.

Take away the timber or steel and SIPs can be complemented by engineered lumber and 2x lumber to take on the loads. Referred to as "SIP structural" buildings, the panels are used in place of conventional stick frame construction, thus eliminating 16-inch-on-center studs.

 

Whole-Wall R-value vs. Center-of-Cavity

And with the elimination of studs, so goes the loss of heat from having wood – a poor insulator – every 16 inches. Some studies show the "thermal break" of wood studs can account for as much as 40 percent of a home’s heat loss.

Panels vary in thicknesses based on the insulation choices and the desired R-value. R-value is the measurement used to determine a product’s ability to impede heat flow; the greater the R-value, the higher the resistance.

When determining the R-value of a wall or roof section, all components should be taken into consideration. Studs only provide an insulating factor of R-5, or about R-1 per inch of depth. And insulations such as batt fiberglass will often settle or move within a wall cavity, creating passages for heat to leave a home.

In a SIP wall, the R-value is continuous across the entire plane of the wall with little-to-no breaks. In an R-value battle of between panels and stick frame, SIPs win.

"For improving the energy efficiency of our building enclosures, reducing air leakage and eliminating the common thermal bridges of our insulation are two important objectives," says Jeff Gephart, a state-certified energy rater. "Structural insulated panel construction, when properly executed, can result in lower air leakage rates than often seen in conventional frame construction."

 

 

The Benefits

Speed of install is a biggie. Less time on site for any trade is always less money.

Panel systems install twice as fast as stick framing, reducing labor costs. With SIP structural projects, much of the job can be pre-cut in the shop – openings for windows and doors can be cut out before panels get to the site – and wall sections up to 24 feet long can be pre-connected then craned into place. Those methods not only reduce assembly time but also greatly reduce job site waste.

SIPs also provide significant energy savings.

Researchers at Foard Panel Inc., a SIP manufacturer and installer in West Chesterfield, N.H., have seen real energy-performance results in many of their projects over the last 15 years.

For instance, a 12,000-square-foot warehouse building in New Hampshire, built with R-30 structural panel walls, spends $3,000 a year on heating fuel. A timber frame home enclosed with SIPs in Brattleboro VT received a Home Energy Rating of 46 – meaning the home performs 54-percent better than the energy standards set in 2006.

 

Green Building Certification

SIPs are a recommended building system for all green certification programs including ENERGY STAR®, LEED (Leadership in Energy & Environmental Design), and the NAHB (National Association of Home Builders) Model Green Home Program.

SIP buildings have been exceeding required thermal performance levels for all these certification programs. The testing includes certified energy raters and blower door tests, which measures the rates in which air leaves or enters a fully enclosed building. SIP panel buildings score well on such tests due to their low air infiltration rates.

Because SIPs create near air-tight buildings, special attention must be paid to choosing mechanical systems. Boilers and air conditioners can be sized smaller – meaning more money in the homeowner’s pocket. And the use of an energy recovery ventilation system (ERV) – a relatively low cost in relation to the full cost of a new home – will ensure healthy indoor air quality.

And homes proven to meet energy-performance requirements can qualify homeowners and builders for tax credits and rebates. In Vermont, ENERGY STAR® certification for new construction is free. Homeowners and builders can start the process by calling Efficiency Vermont.

Besides meeting energy performance requirements, SIPs also contribute to multiple LEED points for recycled content, waste reduction and low VOC materials. OSB is made from farmed lumber and free of urea-formaldehyde. None of the foam cores off-gas and the XPS foam core is made from recycled material. Because panels can be cut in the shop, there is little waste on the job site. A panel house uses substantially less lumber in the shell compared to stick frame construction.

 

Design & Construction

There’s no limitation in design between conventional stick framing and SIP building. Therefore, you can use any software to create your floor plan from traditional architecture programs to an iPad construction app in order to design your SIP building. Any floor plan figured for stick can be emulated in SIP design. And designing for SIPs from the very beginning can eliminate wasted materials and excess cost. Heard that wiring a SIP home is harder, more difficult, more expensive? Electricians who are familiar with wiring SIP homes say they actually do it for less money than a conventional stick frame building.

And some wiring solutions can even be done after the SIP frame is up and complete.

Most SIP installers have general stick-framing knowledge. And they’ll tell you – basic framing knowledge is all you need to learn how to install SIPs. It’s all the same tools – nail guns, hammers, saws and drills. A few specialized tools may be required to remove foam, like a router with a paddle bit or a "foam scoop" which burns out the foam using a heating element. Those tools can usually be rented out from the panel manufacturer.

Proper sealing of panel connections is essential for reducing air leakage and preventing moisture issues. Sealing is done with expanding foam and SIP-Tape – more detail is always available from the SIP manufacturer.

 

Finding SIPs

Builders can generally purchase SIPs directly through a manufacturer or distributor. To ensure high quality products, use a company that receives 3rd party quality control.

And make sure the company has a long and good reputation.

 

Lisa Ford is the Marketing Manager for Foard Panel Inc. in West Chesterfield, N.H. Gary Dennis is a Project Manager at Foard.


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