An article published in NW Builder magazine ~ by Chuck Dougherty
FASTER, BETTER, SIMPLER
Ever try to build a
building faster, with more quality, and a simpler system? These are some of the
basic qualities of Structural Insulated Panels (SIPs for short). So what are these things? SIPs are building components used for
exterior walls, roofs and floor assemblies, manufactured and precut to your
specifications. They are comprised of a foam core with structural OSB skins
laminated on 2 main faces. The basic
sizes vary from 4 x 8 to 8 x 24.
The foam core thicknesses vary from 3-1/2 up to 11-1/4 to yield
different R-values and strength capabilities.
[See NW Builder July 2000 for some further discussion]
As the skilled labor
pool decreases, we need to make up the quality in the product systems we
choose. A manufactured system like SIPs
can help in many ways. SIPs are
prepared in a controlled environment, which has better quality control and less
dependce on the schedule of the weather. They are not reliant on the diminishing
qualities of dimensional lumber for their fabrication. Their basic strength
characteristics are stronger than standard 2x wall framing. So even before they hit the job site, SIPs
offer a higher quality wall system than jobsite built.
The best way to utilized
SIPs is to have them precut, even though they are available as blanks. Being precut does require your advance
planning for layout, which can be done in the comfort of the office rather than
the job site.
Once on the job site
SIPs tend to be faster to erect than stick built walls, stand them up, foam the
joints, and attach them. But now in
that one trip around the building the structure is up, insulated, and sealed
for infiltration, all with one crew with some minimal training. SIPs tend to be straighter and flatter.
Because of the dimensional and structural stability there tends to be no
drywall seam cracking, leading to less call backs.
Since SIPs are a wood
and foam based system, any work that needs to be done to them can be done with
woodworking tools, and they can be modified in place (with some structural
caveats), if the customer ~ that is when ~ makes any changes. This is also a value in future additions to
the building.
The core of the system is the insulation. SIPs offer an efficient way to get a quality insulated system. In whole wall R-value testing by the Oak Ridge National Laboratory, a 3-1/2 core panel gave a slightly higher R-value than a 2x6 @24 wall. This means that either we can give back 2 of livable square footage (maybe 25sf or more per floor) to the owners, or we can increase the energy performance of the building and use a 5-1/2 core SIP wall and smaller HVAC equipment. Wall temperatures tend to be more uniform and infiltration rate are lower than standard framing systems, these make the indoor environment less drafty and with less heat stratification, all leading to more comfort for the occupant.
Well its such a
great system, there must be some catch.
Since they are pre manufactured at a location probably a ways away from
you job site, good design and planning will pay off, take the time to take a
good look at all the drawings, if you end up needing that one or two last
panels it could be a long truck ride.
We are all getting used to custom products for the building trade, the
SIPs are made just for you, and require lead-time. As a rule of thumb 3 weeks
to review a couple rounds of shop drawings from the manufacturer, and then 3
weeks for production and delivery. These guys can get heavy, over 400 lbs for
the bigger ones. Its best to plan on a crane or forklift to unload and stage, a
crane is almost mandatory for setting roof panels.
Structural Insulated Panels offer to the builder a high value product; a modern engineered component with design flexibility. As energy costs climb, demand for better functioning building will increase. SIPs established performance, strength and modest cost will be an asset in the designers and builders package.
Chuck Dougherty, CPBD
of Synergy Design Group in Vancouver, WA has been design and building with
SIPs and timber frames nationwide since 1984. Phone; 360.573.8082; e-mail
Cddsynergy@cs.com, www.timberframedesign.com. Come visit with him and some SIP manufacturers
at the Portland timber frame Expo 27-29 April 2001.For other information and
a listing of SIP manufacturers contact the Structral Insulated Panel Association
(SIPA) 253.858.SIPA; www.sips.org.