For continuous footings the thumb rule is to provide minimum longitudinal reinforcement near the bottom to resist bending and shrinkage.

Use one or two number four deformed steel bars laid longitudinally near the bottom of the footing as a general minimum for typical residential continuous footings, placed with concrete cover of approximately one and a half inches to two inches so the bars do not corrode prematurely. Tie the longitudinal bars with closed stirrups or U-shaped ties spaced at roughly twelve inches on center to hold their position during concrete placement and to provide shear continuity; if the footing is wide or carries large loads increase stirrup size or reduce spacing per engineer guidance. Where the footing transitions into a stem wall extend the longitudinal bars into the stem wall by a development length appropriate for the concrete strength and bar size usually on the order of thirty to forty bar diameters which for a number four bar is about five to six inches times the diameter factor, and lap splices only where detailed on the drawings. Use concrete chairs or steel supports to lift bars off the soil so they sit at the intended cover height during pouring; do not let bars rest on the subgrade. For sites in seismic or liquefaction-prone zones follow the structural engineer for additional bars, larger stirrups and confinement details because the general thumb rule does not replace project specific seismic design. Always clean rust that is loose and remove mud or oil from bars before placing concrete so bond is not compromised.

Common mistakes include placing bars directly on the soil which reduces cover and bond and can lead to corrosion and weakening of the section, fix this by using chairs or concrete dobies to maintain the specified cover. Another frequent issue is insufficient development or lap length at stem wall connections causing bars to pull out under load, so verify required development lengths with the project drawings or a structural engineer and extend bars accordingly. A third problem is undersized or too widely spaced stirrups allowing longitudinal bars to shift during placement and increasing shear failures, remedy this by tying stirrups at the recommended spacing and checking reinforcement layout before concrete placement.

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