Subfloor construction
The subfloor provides the strength of a floor. Many floors have no separate floor covering on top. The subfloor may also provide services like underfloor heating or ducts for air conditioning.

A ground-level floor can be an earthen floor made of soil, or be solid ground floors made of concrete slab. Floors above may be built on beams or joists or use structures like hollow core slabs.

Ground floor construction
Ground-level slab floors are prepared for pouring by grading the base material so that it is flat, and then spreading a layer of sand and gravel. A grid of rebar is usually added to reinforce the concrete, especially if it will be used structurally, i.e. to support part of the building.

Upper floor construction
Floors in woodframe homes are usually constructed with joists that are centered no more than 16 inches or 40 centimeters apart, according to most building codes.[citation needed] Heavy floors, such as those made of stone, are more closely-spaced. If the span between load-bearing walls is too long for joists to safely support, then a heavy crossbeam (thick or laminated wood, or a metal I-beam or H-beam) may have to be used. A ‘subfloor’ of plywood or waferboard is then laid over the joists.