JLC Live
​New England 2016
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W01 - SIPs as the Backbone of an Integrated Systems Approach to Building, Part 1Wednesday, March 16 from 9:30 AM to 12:30 PM |

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W05 - SIPs as the Backbone of an Integrated Systems Approach to Building, Part 2Wednesday, March 16 from 1:30 PM to 4:30 PM
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March 16, 2016

Originally written:  May 2005

Let’s imagine that we are Martians coming down to earth and seeking to build ourselves a new home for our new life here on this jewel of a blue-green planet.  We are, as Martians of course, well connected to an extraordinary knowledge base and extremely rational in our behavior, but also passionate about the arts. We therefore approach this project almost like a science experiment, but want it to come out looking drop-dead gorgeous!  As well as being concerned about performance-under-fire, we are also extremely cognizant of and sensitive to energy usage and environmental footprint issues.

There have been many threads at the virtual conference table concerning the choice between trusses and SIPs for roofs, HVAC systems for SIPs and the use of an engineer and/or architect.  In my thinking these are all related and it is important for the prospective DIY homeowner to think about the final value of his project being a function of the process utilized to bring it into being.

Even if we choose not to think of the home as an integrated system, Mother Nature (the laws of physics) will have her way.  If the home is conceived of and built in the conventional way with individual components glommed onto a conventional structure we may characterize it as non-integrated, but Mother Nature will experience 

There are two structural characteristics of SIPs that are generally not accounted for in creating the usual “stick translations” that predominate in the residential dwelling market.  They are the fact that SIPs are exceptionally high performers when it comes to handling in-plane loads, and that SIP buildings actually behave as thin shell structures, dispersing point loads throughout the entire surface area. These properties may be exploited more consciously in doing the structural analysis of the project and eliminated members that one wouldn’t think of omitting in a conventional stick-frame structure.

1. The first “trick” is to look at dealing with the resolution of ridge or purlin bearing points usually at a gable end wall.  These point loads are usually in the 2,000 lb. – 8.000 lb. Range.  For an extreme case, consider the ridge beam hitting at the peak of a gable end wall.  My SIP load/span charts tell me that for a 6 ½”  thick SIP the per-linear-foot capacity runs from 2000 lbs (12 foot high-30psf wind load) to 8,000 lbs (8 foot high-30psf wind load).  If the design calls for an 8000 lbs  reaction set 20 feet off the floor then it looks like we’re in trouble, as the chart only allows for 5,898 lbs at that height ( all numbers will presume 30 psf wind loading for the rest of this paper).  If the ridge beam is 5” wide, the sill blocking in the bottom of the pocket will be 8” long (1 ½” each side ) which is 2/3 of a foot and therefore capable of only handling 5989 x 2/3 or about 3932 lbs – way under our requirement of 8,000 lbs. 

If we could distribute the load for 2 feet instead of 8 inches we could actually handle 5,898 x 2 or 11,796 lbs, more than adequate with a good safety factor built in. How can we do this?  .....

This question is often asked implying that SIP friendly designs can be built at a very competitive cost compared to stick-built, and that SIP unfriendly designs can be built, but at a premium compared to standard stick-built construction.

I have to say that at least for me this has proven itself to be half true.  We have built some extremely SIP friendly designs that have blown away stick framing schedules by orders of magnitude, but we have also completed some projects where the erection time was been bogged down considerably by some complex geometry.  Let’s review friendly ones first….