What is a setting-out peg?

A setting-out peg is a slim timber or steel stake driven into the ground to fix a point on site. Together, pegs form the dimensional basis of a building: they mark corners, grid lines, service runs and levels before earthworks begin.

What they are for

• Corners and grid lines of a building, patio, shed or wall.
• Level. A nail or mark on the peg records a known level exactly: the finished floor level, for instance, or a round figure below it.
• Service runs for drainage, land drains, cables and foundations.
• Excavation limits of a pit or trench.

In practice

Pegs are by nature temporary and vulnerable: they sit exactly where the excavator needs to work. That is why builders use profile boards (also called batter boards): two posts with a horizontal board across them, set up clear of the excavation. The lines are marked on the board; a string line between two profiles puts the grid line back on the ground at any time, even after the pegs have been dug away.

Step by step on a small job

1. Establish one fixed reference — an existing wall, boundary or benchmark that will not move. Record that level and write down where it is.
2. Drive pegs at the corners, heads just above ground, with the exact position marked by a nail head.
3. Check square using the diagonals. On a rectangle both diagonals must be exactly equal. Otherwise use the 3-4-5 rule: three metres along one side, four along the other, and the diagonal must be exactly five.
4. Set profile boards clear of the work, roughly a metre back from the excavation, and transfer the lines onto them.
5. Record every dimension on paper or in a photo, measured from two fixed points, so a lost peg can be reinstated.

Common mistakes

• Driving pegs into loose ground or in the traffic route. They shift or vanish unnoticed — and a shifted peg only shows up once the foundation is out of line.
• Transferring levels by eye or with a spirit level on the ground. Use a level instrument or a water level over the full length; across ten metres a centimetre of error builds up fast.
• Relying on a single reference point. Without a second, independent check, an error in the first point is never caught.
• Setting out without knowing the boundary. When building near a boundary, check the registered position before driving a peg, not afterwards.

Related terms

• Setting out
• Profile board
• Spirit level
• Datum level
• Excavation

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