Layout and Setting Out
This domain tests establishing building lines, datum levels, batter boards, square corners, offsets, and course marks. The exam focuses on transferring dimensions accurately, checking squareness before excavation, and protecting the marks until the work is complete.
Core rules
- Establish a stable datum from a fixed reference, and transfer levels with a level instrument or water level.
- Set batter boards clear of excavation and brace them so they cannot move.
- Use the 3-4-5 method to establish a right angle, then check both diagonals of the rectangle.
- Mark footing lines, wall lines, and column lines with durable nails or paint on the batter boards.
- Offset lines before excavation so the original marks are not lost.
- Check square and dimensions before digging, and recheck after the first course.
Worked example
Set out a 6 m by 8 m rectangular building. First establish one corner with a 3-4-5 triangle: measure 3 m along one line, 4 m along the other, and adjust until the diagonal is 5 m. Then measure the full sides and both diagonals. The diagonals should be equal: the square root of 6 squared plus 8 squared is 10 m. If both diagonals measure 10 m, the rectangle is square. The reasoning is that a single 3-4-5 check fixes one corner, but equal diagonals confirm all four.
Traps
- Checking only one diagonal and assuming the rectangle is square.
- Letting string sag or using elastic string.
- Moving batter boards after setting out without rechecking.
- Losing the original marks during excavation.
Key points
- Establish a stable datum and protected batter boards.
- Use 3-4-5 for the first right angle.
- Confirm squareness with equal diagonals.
- Offset lines before excavation.
- Recheck dimensions after the first course.