Setting Out and Site Preparation
What the domain tests
Setting Out and Site Preparation tests transferring building position and levels from drawings to the ground: site clearance, datum, profiles, grid lines, squaring, levelling and excavation.
Core rules
- Establish a datum and transfer levels with a dumpy level or laser level; record readings in the site diary.
- Set out from the building line or grid, not from a boundary unless the drawing says so.
- Square corners with the 3-4-5 method or by checking diagonals. A true rectangle has equal diagonals.
- Profiles or batter boards carry lines at the wall face; string lines should be taut and protected from disturbance.
- Verify dimensions, right angles and diagonals before excavation.
- Strip topsoil and stockpile it; provide temporary drainage and protect services.
Worked example
Set out a 12 m x 8 m rectangle. Mark A, B, C, D with AB = 12 m and AD = 8 m. The diagonal should be the square root of 12 squared plus 8 squared, which equals 14.422 m. If AC measures 14.47 m, the rectangle is out of square by about 48 mm and must be adjusted. Reasoning: equal diagonals prove a rectangle; 3-4-5 gives an initial right angle.
Traps
- Measuring along the boundary instead of the building line.
- Skipping the diagonal check.
- Disturbing pegs or string lines without rechecking.
- Mixing datum levels between drawings and site.
- Excavating before services are located.