Will someone please recommend a 6" long screw to attach real stucco wire mesh through 3" of Extruded Polystyrene (XPS) and 3/4" plywood to a 2x4 wood stud.  Thinking of using a 6" long screw because it will bite into the wood stud 2.25".  Since this screw will have quite a bit of leverage on it, good shear and tensile strength will be required to carry the weight of 1.5" of real stucco.  This screw should have reasonably coarse threads suitable for fast installation into the wood stud and also be weather resistant since it will be in contact with the stucco which will always contain some moisture.  Also could the recommendation include the type of washer or cap under the screw head to keep the wire mesh from slipping out.  Additional facts such as the diameter of the screw, and how far apart it should be installed (spacing) and the type of drive head (square, hex head, etc.) is also needed.  

In addition to having the 6" long screws through the EPS, would it be prudent to also use 3M Super 77 spray adhesive to attach the EPS to the 3/4 plywood?

Please make your recommendations for the above requirements based primarily on what it will take to permanetly assemble the composite wall.  Later we may get into discussions about whether the total amount of insulation is appropriate for the climatic conditions.

I think that previous discussion of this suggested a "brick ledge" to support the stucco. Or go with thinner fiber reinforced stucco and skip the mesh. If not, then I suspect that the weight should be supported through the glue and stucco/foam bond and not the screws/mesh. SCIPs have shown that a foam/concrete/mesh wall can support itself. Screws and wood expansion/contraction may just create concentrated tension points that lead to cracking.

Jonr,

Thank you.  Good suggestions.  I like the idea of eliminating the screws.  Moving the 1.5" stucco and 3" XPS over to be fully supported by the concrete slab should remove the need for screws especially if the wire mesh is eliminated.  Does anyone foresee any problems with this new scenario? 

What about the thermal break? Perhaps something like this (blue = foam, white = concrete/stucco):

Your drawing insulates well but being in heavily infested termite country I was trying to keep the foam at least 6" above grade on the walls.  I do not know if the code official will accept foam down into the earth even if it is covered with stucco.  They will probably allow foam under the slab although it may have to be borate treated.  If we go forward with any of the foam ideas, then I plan to find out what the code official will allow.

Perhaps between the two largest blocks of foam put a plastic plate - this will force them to go around it and be detected.

Jonr,

Do you think the attached drawing will meet code regarding termites by using borate treated EPS.

No idea about code but I see nothing in the drawing that they could eat. Concrete/foam/concrete - a typical SCIP wouldn't work?

Time is of the essence and we need to use something that can be done with local crews.

I believe that everything in my drawing agrees with the code but that does not matter.  What matters is how the Chief Code Official feels about it.  Since we now have Formosan termites in our area I believe drawings will get more scrutiny.