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 structural engineer.
The following are some rules of thumb to remember
in a foundation:
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 corners.
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 rebar.
Category Construction Glossary