Estimation, Costing and Construction Management
Estimation, costing and construction management covers quantity take-off, rate analysis, approximate estimates, contracts, valuation and network scheduling. BTSC JE papers frequently ask for plaster, concrete or earthwork quantities and CPM floats.
Core rules
- Approximate estimates: plinth-area rate, cubical-content rate, unit-rate method and service-unit method.
- Centre-line method suits walls meeting at junctions; long-wall/short-wall method needs careful corner deduction.
- Earthwork volume uses mid-section, trapezoidal or prismoidal formula; prismoidal is most accurate.
- CPM: total float = LS − ES = LF − EF; critical path has zero float. PERT expected time = (to + 4tm + tp)/6 and variance = ((tp − to)/6)².
- Rate analysis adds material, labour, plant, overheads and contractor profit; wastage is added to material quantities.
Worked example
A wall 10 m long and 3 m high has a door 1 m × 2 m. Gross wall area = 30 m²; deduct the door = 2 m²; net = 28 m². Plastering both faces gives 28 × 2 = 56 m². At Rs 180/m², cost = 56 × 180 = Rs 10,080. For openings of 0.5 m² or less, standard practice is not to deduct.
Traps
Forgetting to double the area for two faces; deducting small openings that should be ignored; mixing centre-line and long-wall methods; treating free float as total float; adding profit before overheads in rate analysis.