Rebar refers to steel rods, which are put in footings and grade
beams in a concrete foundation. These could vary in size
depending on the structure and what size foundation is being
poured. Rebar used in residential construction is normally #4 or
#5 rods. Rods specified as #4 are ½ " in diameter. The soil type
is one of the major factors that determine the size, placement,
and quantity of rebar. Some will require the services of a
The following are some rules of thumb to remember in a
Footing rebar should be held up with rod chairs or supports at
least two to three inches from the bottom of the footing.
Rebar should be at least one and half inches from the side
of forms or side of footing.
The rebar should lap at least forty times the diameter. Example:
#4 rebar should lap at least (40 * 1/2 inch = 20 inches).
Rebar should be tied with tie wire at least twice at every lap and
Sometimes when conditions require it, a rebar grid is used
instead of wire mesh as shown in the upper right picture. The
grid size will be determined by the structural engineer or builder.
This rebar grid also needs to be held up from the bottom.
The footing rebar in the middle right picture is not placed
correctly. The rebar is resting on the bottom of the footing which
prevents any concrete from getting under the rebar. Concrete's
main strength is compressive. If the rebar is on the bottom of the
ditch, the footing will not be strengthened by the rebar. Also
rebar should be totally encased in concrete . Exposure to dirt,
moisture, and air will provide a path for corrosion into the footing
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Category Construction Glossary