Wall footing detail — recommended depth (thickness) of lean concrete bed (PCC) For a wall footing with a lean concrete leveling bed at the bottom, what is the usual rule-of-thumb for the depth (thickness) of the PCC bed relative to its horizontal projection beyond the wall base on each side?

Introduction / Context:
Lean concrete (plain cement concrete, PCC) is commonly provided beneath masonry wall footings as a leveling course, to distribute loads uniformly, and to create a clean working surface. Designers and estimators often use simple proportioning rules for the PCC bed to ensure adequate stiffness without waste.

Given Data / Assumptions:

• Masonry wall footing with PCC leveling course underneath.
• Projection beyond wall base refers to overhang of PCC on either side.
• Rule-of-thumb practice as used in basic building construction.

Concept / Approach:

A practical proportion is to set the PCC depth approximately equal to its horizontal projection beyond the wall base. This produces a roughly triangular load spread through the PCC, aiding uniform bearing and minimizing edge breakage. Fixed minimal values (10–15 cm) may apply on small projections, but the proportional rule covers a wider range of cases more robustly.

Step-by-Step Solution:

Verification / Alternative check:

Elementary texts and schedules of rates often note t = p for simple wall footings; structural designs may refine these values using bearing checks and settlement criteria.

Why Other Options Are Wrong:

• Fixed 10 cm or 15 cm does not scale with projection and may be inadequate or wasteful.
• “Less than projection” provides less stiffness and edge protection than customary practice.

Common Pitfalls:

• Neglecting proper compaction of subgrade leading to differential settlement.
• Omitting DPC where required, allowing rising damp into masonry.

Final Answer:

Equal to its projection beyond the wall base.