Talking with my neighbor that is building a high-end earth home, he was complaining about how much termite-proofing cost. I said, "You don't have a single piece of wood in the entire stucture. Why are you worried?" He said the termites LOVE to burrow through foamboard. I gave him a deer-in-the-headlights-look followed by an "OH SH@#^@"
So how do you protect any ground contact structure from termites?
"You must be the change you want to see in the world." "First they ignore you, then they laugh at you, then they fight you, then you win." --Mahatma Gandhi
"Preach the Gospel always, and if necessary, use words." --Francis of Assisi.
"Family farms work when the whole family works the farm." -- Adam Klaus
Termites love moisture, and cardboard is their favorite candy. I think that Boron based termiticides are the safest and best way to treat wood. When I build my wofati, I will spray the outside of the structure with Timbor before I put down the plastic. It penetrates the wood 2", and will kill termites and carpenter ants.
Termites have to have a source of moisture to stay alive. That is the reason they build the mud tunnels is to bring the humidity with them when they are traveling back and forth between the nest and whatever they are eating, and the reason they will bore through foam board.
Terminix in Louisiana has gone to a bait system to battle the termites. The bait is more attractive than the building structure, so they go to it first and eat the poison. The poison is carried back to their nest. This is the only method I know of that will effectively battle the Formosan termite.
The Formosan termite comes from Japan and is a super termite. I used to call them kamikazi termites when I was a termite treater! They will eat through the mortar in brick to get to wood! They will eat till it kills them, then the next in line pulls them out of the way and does the same until they punch through to the wood. They will also eat through a telephone pole in the same manner! The very center of the pole has little or no treatment and they will eat their way through to it. I watched a time lapse video where the termites ate the telephone post and dropped the post to the ground, one by one, on a street in Hawaii.
A termite nest can be as much as 14' deep in the ground, just like ant nest. Termite's natural predator is fire ants, so remember that next time you get bit by one!