Question Foam board is to be applied to the exterior of a section of a Concrete Masonry Unit (CMU) wall from 6" below grade to within one foot of wood frame and siding. Along the top of the foam board there will be metal flashing, nailed to the CMU with caulking between the CMU and the flashing. The flashing will not extend to the wood. The idea is to not have any hidden space where termites could get to the wood. Will caukling be a barrier to termites? Any type of cauking? Or a better idea?
Pressure-treated wood or metal are the usual termite barriers between the foundation and sill plate. Keep in mind that termites can construct shelter tubes over virtually any kind of barrier (see http://www.livingwithbugs.com/termite.html and follow links to termite entry). The key to preventing termite damage is pre-construction treatment of the soil around the building and post-construction monitoring and/or baiting (see http://www.livingwithbugs.com/termite_baits.html) - there is no single treatment or construction technique that will prevent termites permanently. Post a follow up if you have questions.
I can answer questions about the control of pest insects, spiders, mites and related arthropods. These household pests include termites, carpenter ants, powderpost beetles, nuisance ants, bed bugs, cockroaches, fleas, wasps, and many others. I can also answer questions about using pesticides and other pest control tools such as baits and traps.
I am a retired university extension entomologist. I've taught and conducted research in urban and agricultural entomology. I've published over 70 extension publications, 20 research publications and several books about insects.