IMPORTANT INFORMATION:
in areas that are prone to termite problems use foam insulation that  is termite resistant.   

http://www.energycodes.gov/support/slab_faq.stm

Dura-R10 Foundation and slab Insulation

DODGE THE TUBING DOWN AND UNDER EXPANSION JOINTS

EXPANSION JOIST

To use 6" or 8" spacing you  can use this method to control the size of the end loops.