| Primary value | 230 mm (300 mm preferred for G+3+) |
| Applies to | Tie beams between isolated column footings · Plinth band carrying the brick wall above · Seismic Zone III–V buildings (mandatory) |
| Exceptions | G+3 and above → 300 mm depth |
| Wide span (> 5 m between columns) → 300–450 mm depth | |
| Width to match wall above → 230 or 300 mm | |
| Minimum reinforcement → 4 × 12 mm bars (2 top + 2 bottom) | |
| Measured as | Overall depth of the plinth beam from soffit to top, sitting on top of pedestals or short columns at the plinth level. Width usually matches the brick wall above (230 or 300 mm). |
| Source | IS 13920 — Clause 5.5 (tie beams) 📚 Cross-referenced |
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Plinth beams tie the column footings together so they settle uniformly and resist seismic shear at the base. 230 mm depth is the absolute floor below which the beam can't develop the moment needed to engage adjacent footings. In Zone III–V, IS 1893 mandates ground beams between every column pair.
Indian residential builders default to 230 × 230 mm plinth beams for G+1 / G+2 and step up to 230 × 300 or 230 × 450 for G+3+. Skipping plinth beams entirely (still common in informal construction) is the most visible cause of differential settlement cracks at the plinth band.