In the long-and-short-wall method of estimation, the length of a long wall is taken as the centre-to-centre distance between walls plus which allowance?

Introduction / Context:
The long-and-short-wall method is a classic approach to estimate quantities of masonry. It distinguishes between external (long) and internal (short) walls and prescribes how to compute their lengths for volume or area calculations.

Given Data / Assumptions:

• Long walls are measured out-to-out; short walls in-to-in.
• Centre-to-centre spacing and wall thickness B are known.
• We seek the correct allowance for long-wall length.

Concept / Approach:
For long walls, out-to-out length = centre-to-centre length + half breadth at each end (total +B). For short walls, in-to-in length = centre-to-centre length − half breadth at each end (total −B). This ensures joints and overlaps are correctly accounted when summing item quantities.

Step-by-Step Solution:
Long wall out-to-out = L_c/c + 0.5B (left) + 0.5B (right) = L_c/c + B.Therefore the rule is “add half breadth on each side”.Select option that states this explicitly.

Verification / Alternative check:
Worked examples in estimation textbooks consistently apply +B for long walls and −B for short walls when moving from centre lines.

Why Other Options Are Wrong:

• A overstates the rule (adds full breadth at one end only).
• C is an arbitrary fraction not used.
• D ignores necessary out-to-out allowance.
• E reverses the correct adjustment.

Common Pitfalls:
Applying the same sign for both long and short walls; forgetting to adjust at junctions and for openings.

Final Answer:
Half breadth of the wall on each side (i.e., add 0.5B at both ends).