Posted By Dennis Nelson on 09/27/2007 6:54 PM
Only a problem if the snow load is 200lb/ft and the span between supports exceeds that of the manufacturers testing data.
Before you spec a product for your application, research it and understand its capabilities.
If a SIP manufacturer's testing data shows that an 8" roof panel with panel spline connections mathematically will work for a roof load of 40psf and the span is borderline for that value, don’t roll with it to save a couple of bucks. Understand, you are choosing a premium product for your application and use something that wont deflect over a duration.
Personally, I even frown on double lumber connections. If you cant use I-joists, or have to use (2)2x's as a spline, maybe substitute for an alternate engineered lumber. This will not only provide for an easier installation (as engineered lumber dimensions are typically more true) it will also eliminate any seams. I’ve heard stories of 'being able to view light' through double lumber splines, even when following manufacturer guidelines for mastic application.
Where are you building?
What is the engineering data for your site?
Spans? Loads?
Gotcha. I actually already built the house (southwest lower Michigan). I trusted the panel manufacturer to "do the math" and design it appropriately. Additionally, my building inspector required the detailed plans and sign-offs. I ended up for various reasons to go with a traditional 2' O.C. roof truss package that the 8.5" panels sat on top of. The panels are 8' x 17'. I am pretty confident the panels are very solidly put together. The splines cause an overlap of 2-3 inches and are foamed-glued and nailed in place.
In any event, the house is done, so I guess I will see over time.