Estimating, Costing and Valuation
This domain tests the types of estimates, the two standard methods of working out quantities, correct measurement units, rate analysis, and the vocabulary of valuation such as depreciation and scrap value.
Types of estimates
- Approximate or preliminary estimate by plinth area rate or cubical content; detailed estimate from drawings and a bill of quantities; revised estimate when the sanctioned amount is exceeded; supplementary estimate for extra work.
- Plinth area rate method: cost = plinth area × rate per m². Cubical content method: volume = plinth area × height, then multiply by the rate per m³.
Methods of taking out quantities
- Centre-line method: total centre-line length × breadth × height, then deduct openings.
- Long wall–short wall method: long walls measured out-to-out, short walls in-to-in.
Units and valuation
- Earthwork, concrete and brickwork in m³; plaster, painting and DPC in m²; steel in kg or quintals (1 quintal = 100 kg); doors and windows by number.
- Valuation terms: depreciation, scrap or salvage value, sinking fund, book value, market value, and standard rent fixed under rent control.
Worked example
A room is 5 m × 4 m inside with 0.23 m walls and 3 m height. Centre-line length = 2(5 + 0.23) + 2(4 + 0.23) = 10.46 + 8.46 = 18.92 m. Brickwork = 18.92 × 0.23 × 3 = 13.05 m³. Deduct a door 0.9 × 2.1 × 0.23 = 0.43 m³ and a window 1.2 × 1.2 × 0.23 = 0.33 m³, leaving about 12.29 m³.
Marks-losing traps
- Forgetting to deduct openings, or deducting them without adding back the jambs and sill.
- Using plinth area when the question asks for carpet area.
- Mixing units: plaster is m², never m³.