Drawing, Estimation and Costing
Scope
This domain tests reading plumbing plans and isometrics, taking off quantities, rate analysis and preparing estimates. The exam expects correct units, wastage and labour content.
Core rules
- Read the scale, symbols, pipe sizes, levels and legend before measuring.
- Use centreline or measured take-off methods consistently; measure pipe in metres, fittings in numbers and fixtures in numbers.
- Add wastage, commonly 5–10% for pipes and fittings, and include labour, transport, overheads and profit.
- Keep the bill of quantities item-wise: description, unit, quantity, rate and amount.
- Show assumptions and exclude items clearly; add applicable GST separately.
Worked example
Estimate 18 m of 25 mm GI pipe. Pipe: 18 m × ₹200 = ₹3,600. Fittings: 8 elbows × ₹60 = ₹480; 4 sockets × ₹40 = ₹160; 2 unions × ₹150 = ₹300; fittings total ₹940. Wastage at 5% on ₹4,540 = ₹227. Labour: 18 m × ₹50 = ₹900. Total = ₹3,600 + ₹940 + ₹227 + ₹900 = ₹5,667, plus applicable GST. Reason: fittings and wastage are real costs, not extras.
Traps
Forgetting fittings; using the wrong unit; no wastage; mixing labour and material rates; not reading the scale; omitting taxes or assumptions.