I am in the planning stages of building a two unit townhouse and have some questions regarding the ability to construct with a SIP floor. Each unit will have a ground floor footprint of 30’ x 44’ with a second floor roughly 30’ x 22’. This will be constructed over a crawlspace with a cathedral roof/ceiling (8” SIP) supported via ridge beam and purlins spanning the 30’ length to beam pockets in the SIP exterior and common wall (6” at this point). I have attached a .pdf of a rough layout with a few interior walls shown (sorry, not a draftsperson).

My study of SIP construction (I am not an engineer either) leads me to believe that this sort of arrangement would transfer the roof load to the walls as well as a portion of the 2nd floor as I prefer to use the balloon/ledger SIP detail to support some of the 2nd floor.

In reviewing the span tables of a SIP manufacturer close to my locale (IB Panels in Jerome ID) I see that for a DL of 1/360 and a 40 psf live and 10 psf dead load they show a 6” SIP with 1 2x6 will span 11’ or a 8” SIP with no 2x would span 11.5’. This table doesn’t quite work as the 2nd floor changes the design loads (40 live & 20 dead ???) and a little stiffer floor would be preferable. With that in mind, I was thinking that pony walls at 10’ centers would decrease the span enough to use this load table for planning purposes.

I know that this will all require a structural engineer to evaluate but wanted to get a quick blush opinion from some experienced SIP folk as to whether they think this set-up is feasible and likely to pass structural muster. Is it overkill? Is the 10’ on center spacing inefficient for SIP panel manufacture or can a 30’ long panel be had? Also, I would prefer to use a SIP with an I-joist spline, what size SIP would be most likely in a configuration like that and could that lead to longer spans and maybe only 1 pony wall in the center (15’ span)?

Hope this is clear enough and thanks in advance for any insights that anyone can lend.

3cityblue,

Assuming that you want the SIP floor for an insulation factor between the living space and the crawl space, I think if the proper engineering is done, this could work. What I’m thinking is that you would want a dimensional lumber spline between the SIP panels at the point where the weight-bearing wall from the second story meets the first floor and the proper supporting structure in the crawl space. Although this may be possible, it may not be desirable. If you have sewer and water lines in the crawlspace, with no heat, it would expose them to freezing temperatures, resulting in frozen pipes. A better idea might be to use ICF’s in the construction of the foundation, conventional I-joists and insulate below the water and sewer pipes, or just insulate the crawlspace.

Steve
GrandCountySIPs.com

Thanks Steve,
I was planning on using ICF for the walls and keeping the crawl space unvented so freezing of sewer and a few PEX water lines shouldn't be a problem.  Rarely get sustained freezing spells in this area so should be ok.  Thanks again.

SIP Floor insulated crawlspace with 8" SIP and laminated with .42" fibercement underlayment on this balloon framed 2  story currently being built in New Orleans

Chris, What is the span and deflection on that floor?

Posted By GuyB on 31 Mar 2010 10:44 AM
Chris, What is the span and deflection on that floor?

Guy ................. 13 ft.   L/360    55#

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