Performs site preparation and layout
This domain covers establishing control on the site: bringing a known elevation and a known line onto the property, transferring them to stakes and strings, and proving the layout is square and at the right grade before excavation begins.
Control and datum
A benchmark is a fixed point of known elevation; a datum is the reference elevation from which the building is set. Elevations are transferred with an automatic level, a transit or a laser, and recorded so they can be re-established after excavation. Batter boards are set back about 1.5–2 m from the excavation so lines can be restrung, and are levelled to the same elevation before any line is run.
Squaring and setbacks
The 3-4-5 method (or 6-8-10) sets a right angle: from a corner, measure 3 units along one line and 4 along the other; when the diagonal between the marks is 5, the corner is square. The stronger check is diagonal comparison - the two diagonals of a rectangle must be equal, measured between matching points. Zoning setbacks, easements and utility locates are confirmed before the first cut; locates are a legal requirement in every province.
Grade and excavation
Grade stakes and a laser show cut and fill. The excavation is taken to bearing soil at the footing width and depth from the drawings; foundation drains lead away from the building, and final grade slopes away from the wall so water does not pond at the footing. Disturbed fill cannot be assumed to carry a footing without an engineer's direction, and deep excavations require shoring or sloping as the regulations require.
Worked example
A 9.0 m × 12.0 m building is being squared. The theoretical diagonal is √(9.0² + 12.0²) = √(81 + 144) = √225 = 15.0 m. Even after a 3-4-5 check at one corner, both diagonal measurements must read 15.0 m; if one reads 15.1 m the rectangle is a parallelogram, and the short corner is moved half the difference until the diagonals match.
Traps
Measuring diagonals from different reference points; ignoring string-line sag on long spans; trusting a level that has not been checked; and excavating before the locate ticket is closed.