Termidor SC cannot be applied indoors or for flea control. We do carry an Indoor Flea Kit that will be great for this application. You will vacuum daily (discarding the bag or emptying the canister after each use) and spray once every two weeks. It is highly recommended to make a minimum of two applications indoors but may require additional applications depending on the level of fleas.
If the footer is right below the dirt level, within 6 inches, and it comes out 12 inches, then you should make your trench out where the footer ends. In other words, instead of digging a 6 inch trench directly against the structure, you will move the trench away from the house where you can dig down past the footer. You should still treat the soil in between the trench and the house (where the soil sits on top of the footer) by just drenching the soil if you can.