Since its detached i would treat around the perimiter with Taurus SC( same agent as Termidor, only less expensive) a fipronil agent that is not detectable/slow kill and will be carried back to any nest( including termites). Then you could spray with a couple of times a summer with Demon wp( Cypermethrin 40%) as a preventative, which is way cheaper than Taurus/Termidor).
The way it works is you trench around your foundation (~ 6" deep x 4" wide) and pour in the pre-mixed Taurus SC around the foundation. Do not "spice it up" as it is a slow kill that is carried back to the nest. It is designed for them to not detect it as the go through.
The Demon, or my other favorite is Bifenthrin (Talstar, Bifen IT) is sprayed on active sites This they detect and will run from while dying.
Termites are persistent little suckers so if you treat around your house with a repellent insecticide they will systematically poke around and find a weak areas to go through. With the Taurus (Fipronil) they do not detect it and it rubs off on other termites as they pass each other. In a few days the whole colony is sick and dies.
Always use per the label instructions for concentration and rate so us DIYer bug sprayers don't get a bad reputation for killing all the bees.