Centre line method of estimating a building — key rules: Identify the correct statements about using the centre line method to compute quantities for walls and associated items in a building.

Introduction / Context:
The centre line method is a fast and reliable estimating technique for buildings with repetitive wall geometry. Instead of measuring each wall face separately (long-wall/short-wall), quantities are obtained using the total centre line length multiplied by item-specific cross-sections, with careful junction corrections.

Given Data / Assumptions:

• Rectangular/symmetric planning so that junction corrections are systematic.
• Different wall thicknesses (e.g., main wall vs. partition) may exist.
• Items measured include excavation, foundation concrete, brickwork, and DPC where applicable.

Concept / Approach:

For any layer having uniform cross-section, quantity = centre line length * cross-sectional area. When wall thickness changes or walls intersect, the centre line length requires adjustments (usually by half the meeting wall thickness at each junction) to avoid double counting.

Step-by-Step Solution:

Verification / Alternative check:

Cross-check with long-wall/short-wall method on a small bay; both should match within rounding if junction corrections are applied properly.

Why Other Options Are Wrong:

• Options (a)–(c) are individually correct; hence “All the above” is the right consolidated choice.

Common Pitfalls:

• Forgetting to recompute centre line for different wall thicknesses and offsets.
• Omitting half-thickness deductions at T-junctions and cross-junctions, causing quantity inflation.

Final Answer:

All the above.