Setting Out and Measurement
Domain 5 covers Setting Out and Measurement: transferring a drawing to the ground accurately and then recording site measurements correctly. Marks are lost for using the wrong reference line or the wrong unit.
Setting out a building
- Fix two reference pegs for the front line and mark the centre line of the outer wall.
- Use the 3-4-5 method to set a right angle: measure 3 m along one line, 4 m along the other, and adjust until the diagonal is exactly 5 m.
- Set the remaining corners, then check both diagonals; they must be equal for a true rectangle.
- Mark foundation trenches from the centre lines by adding half the wall thickness plus the offset for working space.
- Use batter boards and string lines outside the excavation so the lines survive digging; transfer levels with a level or a hose pipe.
Measurement on site
- Record in a field book: description, number, length, breadth and height, in metres to two decimals.
- Units: linear m, area m², volume m³. Brickwork and concrete in m³, plaster and painting in m², steel in kg or quintal.
- Measure brickwork between centre lines of walls and deduct openings above the specified size.
Worked example
A room is to be set out 6.00 m × 4.00 m. After fixing three corners with the 3-4-5 method, the diagonal is checked: √(6² + 4²) = √52 = 7.21 m. Reasoning: if the measured diagonal is 7.25 m, the corner is not 90°; shift the peg until both diagonals read 7.21 m within about 5 mm.
Traps
- Measuring the trench from the outer face instead of the centre line.
- Trusting one diagonal only.
- Mixing millimetres and metres in the same measurement sheet.