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Frequently Asked Questions
MAIN PAGE
WHAT ARE SIPS?
EXPERIENCE
WITH SIP PANEL HOMES
WHY
SHOULD MY NEW HOME BE A SIP PANEL HOME?
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Q: What is a SIP?
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SIP stands for Structural
Insulated Panel. Most SIPs consist of two layers of wood sheathing
laminated to a foam core. Some SIPs come with other facing materials:
metal, drywall, fiberboard, even plastic. When installed in a home,
the SIP provides both structure and insulation. While most commonly
used in walls, SIPs can also serve as load-bearing floor, ceiling and
even foundation components. Most SIPS are designed carry the entire
range of structural loads in a building; however, SIPs with one
drywall facing are just used as cladding panels around timberframe
structures. (Note: A related category of SIPs doesn’t use facing
materials; they use either wood or steel framing members placed
between or within tall blocks of foam.)
Q: What gives a SIP its
strength?
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The resulting sandwich panel
product acts like an engineered I-beam, resisting both compressive
forces from above and buckling forces from the side. Engineering
tests show that, depending on the type of structural test being
administered, SIPs range between two and seven times stronger than
traditional framing. In some SIPs, integral studs used as splines for
joining panels together also help carry the structural load.
Q: Are the high
efficiency claims valid?
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Four key factors make the
average SIP home very energy efficient. First, foam provides higher
insulating value per inch than traditional fiberglass insulation.
Second, there is much less wood framing within the typical panel,
which again increases total R-value. Third, the foam is continuous
and is not susceptible to the commonplace flaws found in average batt
installations. Fourth, foam doesn’t allow air infiltration around it;
with reasonable attention to detail, panel joints can be sealed to
provide house tightness that averages between 20% and 40% (for house
with wall and ceiling panels).
Q: Does the foam
lose R-value over time?
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Urethane foam stabilizes at a
relatively high R-value (about R-7 per inch) once it is placed in a
home’s wall and ceiling system; at that point, the R-value of a fully
cured urethane panel is about twice that of a fiberglass wall.
Expanded polystyrene insulation (EPS) used in most panels offers lower
R-value (about R-4 per inch) but maintains its R-value once the panel
arrives at the job site.
Q: Are
SIP homes too tight for good indoor health?
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No. Research indicates that
the best way to provide a home with good indoor air quality requires
two essential steps. First, the home has to be built as tightly as
practical; it is easier to control air movements in a tight home than
in a leaky one. Second, you need some upgraded mechanical ventilation
features that can provide a steady flow of fresh air.
Q: Can SIPs be
used in a passive solar home?
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The National Renewable Energy
Laboratory (NREL) designed a number of passive solar homes that were
eventually built in the sunny but cold climate at the South Rim of the
Grand Canyon. Researchers found that the SIP building shells
actually performed better than expected. SIPs and solar can work well
together, as long as heavy heat storage materials, such as a concrete
slab, are included within the building shell. But to be comfortable,
solar homes—built with SIPs or traditionally framed—should incorporate
high-performance, low-e coated window products.
Q: Are building codes a
problem?
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Most panel manufacturers have
listed their products with regional code bodies, which facilitates
acceptance of their products by local code officials. Yet while SIPs
have been around for several decades, some code officials still aren’t
familiar with them, so check with your local building department.
Q: How do you wire SIP
houses?
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Wiring a SIP house takes a
little extra planning prior to construction. Nearly all panels come
with some type of pre-cored chases in the foam. You simply fish the
wire through those chases to where the wire is needed. While panels
are being placed, some minor cuts are normally made to accommodate
switch boxes beside exterior doors.
Q: What about SIPs in fires?
Q: Are ants
and termites a problem in panels?
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No more than in conventional
construction. In climates where either termites or ants can cause
problems, panel manufacturers recommend that all homeowners use the
same preventive treatments (topical sprays around foundations, termite
shields, etc.) they would use in a stick framed home. Note, however,
that foam within panels does not provide food value for insects.
Q: Is a SIP a
“green building product?”
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SIP homes require considerably
less framing lumber than a conventionally framed home. Note too that
95% of a tree can be used when it is cut into wood chips to make OSB
for SIP facings, vs. 63% of a tree when it’s sawn into solid lumber.
SIP homes pre-cut in the factory mean less job-site waste is shipped
to the landfill and more of it is recycled at the factory. While it
takes several times more energy to make foam than fiberglass, and the foam
itself is a petroleum product, lifetime savings in heating and cooling
requirements will offset this difference in favor of the SIP home.
Q: Do SIPs
walls cost more than frame walls?
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Generally speaking, a little
more. The materials definitely cost more, but labor savings should
partially offset any increase. But SIPs can be competitive if the
design is optimized to incorporate them. That means doing things like
designing house dimensions at two-foot and four-foot increments,
pitching roof SIPs up at steeper angles to include loft square
footage, and similar adjustments. A number of builders scattered
around the country use SIPs for their entry-level housing products.
Builders who repeatedly use SIPs have figured out ways to minimize any
cost difference.
Q: Are panels a
nearly foolproof product?
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No. Like anything else,
panel manufacturing requires considerable quality control in the
factory. Make it a point to ask any manufacturer about their QC
process. Additionally, a knowledgeable designer or engineer needs to
review plans to make certain that the panels selected for a particular
plan are capable of meeting the structural loads involved. And later
at the job site, assembling panels into a strong, airtight and
watertight shell requires someone in the lead with some SIP
experience.
Q: Bottom line, are
SIP houses better?
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Assuming the SIPS are properly
designed, manufactured and installed, a SIP house will be stronger,
more energy-efficient, and more comfortable.
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