Yes. While there are some floor heating systems that can be installed beneath floor joists, most electric radiant floor heating systems will need to be installed beneath the floor itself. This is why the best time to install electric floor heating is during a remodel or as a part of a new construction, when a floor is being installed anyways.
If you're interested in alternative radiant heating methods, check out our Radiant Panels, which are wall-mounted and use infrared technology to provide supplemental heating.