Drawing, Estimation and Costing
Drawing, Estimation and Costing tests your ability to read plumbing layouts and convert them into quantities and a priced quotation. Expect plan, elevation and section views, symbols, scale, measurement and rate build-up.
Drawing
Read the floor plan for fixture positions, the riser diagram for vertical stacks, and the isometric for pipe routes. Know symbols for gate valve, check valve, floor trap, gully trap, water meter and vent. Use the stated scale; dimension lines override scaled measurements.
Estimation
Measure pipe in running metres, count fittings, and price material, labour, wastage, overheads and profit. Record quantities in a measurement book. Add wastage, typically 3–5% for pipe, and GST as applicable.
Worked example
20 m of 25 mm CPVC at ₹180/m = ₹3,600; fittings ₹900; material = ₹4,500. Add 5% wastage = ₹225, labour ₹1,200, overhead 8% on material = ₹360. Subtotal = ₹6,285; profit 10% = ₹628.50; quoted price before GST = ₹6,913.50.
Traps
Forgetting wastage and labour; pricing from a scaled drawing after the scale has changed; mixing running metres with numbers of fittings; and quoting a lump sum without a written scope.