Alternatively, the room, room extension, deck or even a house can be built above concrete columns U.S. builders call piers some others call pilasters, another of many term misuses common to building trade parlance.
The floor joists are spaced at 12 in, 16 in, and 24 in on center, depending upon the live load needs of the design the closer the spacing and the wider the floor joist dimension, the less the floor will flex.