Setting out and levelling

Abstract

The position of the building on the site is obtained from the architect’s layout plan or block plan, and will be given relative to the boundaries of the property, roads, adjacent buildings etc. The first operation is to establish a base line, this usually being the frontage line. Stout pegs are driven at each end clear of the building position, the exact position of the frontage line being marked by nails or saw cuts in the tops of the pegs after which a line is strained (Fig. 9(A) and (B)). The flank walls are then set out using a large builders square having sides approximately 3 m (10 ft) long, and right angles checked by the 3 : 4 : 5 method (Fig. 9(B)). This is an application of the Theorem of Pythagoras, and makes use of the fact that any triangle having sides in the proportions 3 : 4 : 5 is a right angled triangle. Too small a triangle may give rise to inaccuracies and suitable lengths of side should be adopted as a basis, so as to give a triangle of adequate size. Thus if 3 ft is taken as a basis then the triangle will have sides 9 ft (3 × 3 ft), 12 ft (3 × 4 ft) and 15 ft (3 × 5 ft). If 1 m is used as a basis then the sides will be 3 m, 4 m and 5 m. When setting out large buildings, where wall lengths exceed 50 ft (15 m) it is advisable to use a theodolite. The main rectangle of the building should finally be checked for square by measuring opposite sides and the diagonals (Fig. 9(C)).