Building Drawing and Estimating
Building Drawing and Estimating tests your ability to read and produce plans, elevations and sections, and to measure and price work from those drawings. You must know drawing scales, line types, symbols and dimensioning, plus estimating methods, rate analysis, bills of quantities and IS 1200 measurement rules.
Drawing conventions
Use a suitable scale such as 1:100 for a building plan and 1:20 or 1:10 for details. Walls are shown by two parallel lines; doors by a leaf and swing arc; windows by glazing lines. Dimension lines should be continuous, with numerals above the line and units stated once. Section drawings show cut surfaces with hatching and levels in metres.
Estimating methods
- Approximate methods: plinth area, cubic content and service unit rates for early cost checks.
- Detailed estimate: measure each item, apply IS 1200 rules, then multiply by rates.
- Centre-line method: find the total centre-line length and multiply by breadth and height; suitable for walls with similar sections.
- Long-wall and short-wall method: long walls are measured out-to-out and short walls between them; suitable for regular rooms.
Worked example
A room has internal dimensions 4.0 m × 3.0 m, wall thickness 0.23 m and height 3.0 m. Long-wall length = 4.0 + 2 × 0.23 = 4.46 m; short-wall length = 3.0 m. Brickwork volume = 2 × 4.46 × 0.23 × 3.0 + 2 × 3.0 × 0.23 × 3.0 = 6.155 + 4.140 = 10.295 m³. Deduct openings separately if any.
Traps
Do not mix centre-line and long-wall/short-wall assumptions in one calculation; do not forget to deduct doors and windows; keep units consistent; and do not price an item without checking the measurement rule and rate basis.