As I've said before I'm looking at doing an icf basement and then sips walls my exterior finish will be brick.  The 3 1/2 inch panels i'm looking at use a single 2x4 spline to join the panels and I would like to use 24' panels.  I was thinking about possibly using 1 1/2 inch rigid foam board from the icfs up to the top of the wall that way the rim joist would be insulated, i wouldn't need house wrap (maybe???) and this would cover the thermal breaks of the 2x4 splines.  Also wouldn't this allow me to use windows with jambs for 2x6 walls?  I understand it will be some added cost about $800 and labor (although it would be my labor).  Anyway i was wondering if anyone saw any problems with this.  thanks

Not really. Styrofoam makes several 'sheathing' foam boards that could be used. You could always just increase the size of your panels, and have them over hang the exterior ICF foam also.

As far as the rim goes, you could always use a SIP rim for that(See an article in the Learning Center).

Good Luck!

PanelCrafters, I am a little surprised you didn't suggest some things that might use SIPS a bit more efficiently, (I think) such as:
Build the entire wall from a single panel (if accessible by truck/crane and if appropriatley sized wall);
Use wider panels to minimize the splined joints;
Land the SIPS panel on a plate directly on the ICF foundation and set/hang the floor within the panel space instead of under it.
Use the above system but spray or rigid foam foam the interior of the floor rim joists.

It seems like a lot of extra and redundant effort to clad the whole SIPS wall with another sheet of foam since given the effiiency of the whole wall system, are the 2x4 splines really that much of a thermal loss point? It also adds additional framing to accomodate the window nailing flanges, etc.

Also, use a house wrap for water control, so your sheathing doesn't rot. 15# is a good inexpensive method, tried and true. Simpler the better.

Well, BlackDog,
This person had a plan, and it wasn't really too bad. I did suggest a larger panel(thickness) and a SIP Rim.

Since there are many ways to accomplish what I call a 'Complete SIP Wrap', I wasn't going to tell him/her that they are an idiot for not doing it 'This Way'.

Splines: There are multiple systems(OSB, 2x, and Custom). Unless you need the support, I consider 2x to be the worst(but he/she had a solution for it). There is also the issue of sealing that connection. Most systems require skill & experience to do it correctly. 2x are fairly easy, OSB a bit more difficult. Custom have their own merits.

I do like Jumbo panels, however, they also have limitations. Large windows will require the manufacturer to build in a header, Doors? I've never seen a large panel span one(someone may do it, but I haven't seen it).

So, I guess the bottom line is that one system(solution) may not be the best system(solution) for all structures.