Measurement and Estimation
This domain tests the units, rules and arithmetic behind quantities, bills of quantities and costing, where a single unit slip costs a whole question.
Units and rules
Earthwork and concrete are measured in m3; brickwork in m3; plaster, painting, flooring and shuttering in m2; steel reinforcement in kg; pipes and mouldings in running metre; doors and windows in numbers or m2. Measure to the specified dimension, not a convenient one. Deduct openings above the stated threshold, commonly 0.1 m2 for plaster and painting and 0.5 m2 for brickwork, following the item measurement rule.
Methods
Long wall-short wall computes centre-line lengths and adjusts for junctions. Centre-line method multiplies total centre-line length by breadth and height, with corner deductions. For a symmetrical building the centre-line method is faster and less error-prone.
Worked example
A 230 mm brick wall 3 m long and 3 m high with a door 1.0 m by 2.1 m. Net area = 9.00 - 2.10 = 6.90 m2. Volume = 6.90 x 0.23 = 1.587 m3. At about 500 bricks per m3, bricks = 1.587 x 500 = 794, plus 5% wastage = 834 bricks. Mortar is the balance, roughly 0.25 to 0.30 m3 per m3 of brickwork.
Traps
Mixing millimetres and metres, deducting a door from one item but not another without checking the rule, forgetting wastage, charging plaster in m3 instead of m2, and using internal dimensions for external work.