Estimation, costing, material take-off and work measurement
Estimation and costing
This domain tests the quantity surveyor side of plumbing: correct units, a complete take-off, and a rate build-up that includes wastage, overheads and tax.
Measurement units
- Pipe and gutter: running metre.
- Fittings, fixtures, taps, traps: each (numbers).
- Excavation, concrete, sand bedding: cubic metre.
- Painting, waterproofing, tiling: square metre.
- Steel sections: kilogram or quintal.
Take-off rules
Measure along the centre line of the pipe, add for fittings by number, count clamps and supports at the specified spacing, list valves, tanks, pumps and fixtures separately, and note lead and lift for material carried far or lifted high.
Rate build-up
Material cost plus wastage (typically 5 per cent), plus labour at the specified constant, plus overheads and contractor profit (commonly 10 to 15 per cent), plus GST as applicable. Show every item; never quote one lump figure for a mixed job.
Worked example
30 m of 25 mm GI medium pipe at 210 per metre, 12 elbows at 45 each, 30 clamps at 12 each, labour 60 per metre. Reasoning: pipe 6300 + elbows 540 + clamps 360 = 7200 material; wastage 5 per cent = 360, so 7560; labour 1800, so 9360; overhead and profit 15 per cent = 1404, so 10764; GST 18 per cent = 1937.52, so about 12702.
Traps that cost marks
Forgetting fittings, clamps and valves; mixing running metre with each; omitting wastage or lift charges; quoting from a phone call without a site visit; leaving GST out and losing margin.