Quantification, Estimation and Work Planning
This section tests taking off quantities, building rates, allowing waste, sequencing work, and planning labour and materials. You should be able to measure from drawings, use consistent units, and explain why an estimate differs from a final account.
Core rules
- Measure net quantities first from drawings, then add a realistic waste allowance for cutting, damage, and offcuts.
- Keep units consistent: metres, square metres, cubic metres, and numbers. Do not mix millimetres and metres in one calculation.
- Build unit rates from labour, material, plant, and overhead; separate supply from fixing where the bill requires it.
- Plan the sequence so that wet trades, services, and finishes do not damage completed work.
- Record variations and dayworks as they happen; verbal changes are difficult to recover later.
- Use a simple programme with dependencies; identify long-lead items such as special doors or roof sheets.
Worked example
Ten door frames each need two jambs 2.1 m long and one head 0.9 m long. Timber per frame = (2 × 2.1) + 0.9 = 5.1 m. For ten frames = 51 m. Add 10% waste = 5.1 m, giving 56.1 m; order 57 m. At LKR 1,200 per metre, material cost = 57 × 1,200 = LKR 68,400. The reasoning: calculate the true perimeter of one frame, multiply by the number, add waste, then price the ordered length.
Traps
- Forgetting waste and ordering exactly the net quantity.
- Measuring an opening instead of the timber member.
- Double-counting shared members such as a common head.
- Leaving variations undocumented until the final account.