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Re: SIPS panels - Structural Insulated Panel System

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Scott gave you some great info. I've not done paid-for design work with SIPs, but investigated them thoroughly about five years ago for my own house.  At the time, I was convinced they were neck-and-neck with sliced bread.  In the end I was faced with the reality of no local installers, and I was looking at a 2x-5x cost premium, and opted for stick instead. (I was pretty sure that Insulspan was planning on chartering a 747 and putting the crew - paid at lawyer rates - up in a 5 star resort during the installation, as they managed a $110,000 quote on a 3000 SF plan)

One think Scott didn't mention (though this will be the Architect's problem) is roofing materials.  As of three or four years ago there was only one, possibly two, asphalt shingle manufacturers who would honor their warranty on products installed directly to the SIP OSB surface.  Additionally, I have some minor reservations about what is going to happen to the OSB during the (inevitable) roof tear-off for the second re-shingle.

Another supplier is FisherSIPS, out of Kentucky, iirc.  At least one of the manufacturers uses 3/8" OSB skins.  There is a whole class of product which uses steel skins with EPS or Urethane/Polyisocyanurate cores. I had a manufacturer in about two months ago who needed local engineering, but can't remember the name or find his card. 

Recently, I've been doing some work with a similar product - Thermasteel panels (www.thermasteelcorp.com). The panels look like light-gauge steel I studs with EPS between them, but are fabricated with 24ga Cs on each face, and EPS foamed-in-place to form a single unit:
 
     _____
[EPS]   ^
 EPS    |
 EPS    |
[EPS]   |
 EPS    4'
 EPS    |
[EPS]   |
 EPS    |
 EPS    |
[EPS]   v

The end channels can be changed out for CSJ/CSW shapes in heavier gauges.  The shapes have a heat-activated adhesive sprayed on the foam side, which bonds to the EPS during the foaming process.  The tensile bond is fairly strong, and the EPS - being continuous - provides a very good resistance to buckling. A 12' tall x 4' w x 7.5" thick test panel (run last Monday) with CSJ studs @ 16" o/c failed at over 40,000lbs, with the load applied at the 1/3 point of the top plate. The failure was a local buckling at the top of the stud, only about 2" at the top was affected.  All this was just to say - the foamed-in-place process really does prevent buckling of thin skins.  That's not to say they are perfect, and I've had several "discussions" with them about their racking shear performance. ICBO values (test/2.5FS) is about as good as drywall on studs if the panel doesn't get diagonal straps. The arguments come because the real life stiffness is deceptively large, as there's no "play" due to fastener/hole slop.

Sorry for rambling on...hope this gives you a little confidence that there are lots of these out in "the wild".  Each has it's own gotcha's, but once you know where the tricks are, the overall performance can be very good.

Jordan



At 04:47 PM 12/7/2004 -0600, you wrote:
I have a project that's a private high school dormitory.  The Architect is very interested in using products that can fulfill multiple tasks.  He has suggested using a SIPS panel as both the roof decking and the load bearing wall.  A SIPS panel is basically 2 pieces of plywood separated by insulation.  The panels are 48" wide and at each joint have actual studs or joist members.  The project is in central Alabama and is IBC Seismic Cat B.  Seismic will be relatively light for this project.  Wind will likely control.  The Architect wants this to be his structural deck (14' span or so), finish ceiling (yes, it's rough), insulation, and shingle nailer.  The walls would be the same except it would receive sheet rock on the interior and hardi-plank on the exterior.

My main concerns are:
1.  With a conventional plywood roof on H-clips there is movement available in the roof.  This product doesn't have this option.  How is this accommodated for this system so that temperature doesn't cause visible roof bulges?
2.  What issues are there with load bearing?  It appears that the plywood is actually taking the load.  It really doesn't give me a warm fuzzy feeling.  What happens if there is a leak that causes plywood failure?  It doesn't seem like it would take much termite infestation to cause a problem.  Bulkier studs are more resistant to both of these.
3.  Bolting a plate down and then installing the panel and then nailing through the panel into the pre bolted sill plate just seems like a crap shoot. 

Has anyone out there used this product and can offer advice?  My gut feel is that it's probably pretty good as a roof deck/insulation/ceiling, but I'm not as comfortable with it as my load bearing wall.  It just seems that you're relying on the insulation to do a whole lot of bracing of the two, thin load bearing wythes.

John C. Jones, PE
Barnett Associates
Pell City, AL
205-884-5334
205-884-0099 (fax)


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