The first step in building setting out is to identify a base line according to the site layout plan. We can establish the base line considering the permanent structures and the relevant distances to structural parts from them as given in the drawings.
Setting out is done based on the principle of “Whole to part”. According to this principle the largest possible rectangle of the building is found and set up first. Then it is further divided into small parts completing the major setting out for the building.
It is very important that setting out process is done in a horizontal plane. When the ground profile is not horizontal proper care must be paid to establish the setting out profiles in a one level. For simple applications a tube filled with water can be used to obtain the levels.
Main instruments involved in this process are Theodolite, Steel and Linen Tapes, Arrows, Wooden pegs, Wire nails and Nylon threads.
After establishing the base line, the main rectangle is set up using the pegs and theodolite. Arrows are used as temporary pegs and wooden pegs are driven for permanent pegs .90° angle is taken by the theodolite and Pythagoras rule is also commonly used for the process. When using the Pythagoras rule proper care must be paid to obtain the largest possible combination of triangles for higher accuracy. Steel tape must be used to measure long distances and it must be tightly stretched when taking the readings.
Wooden pegs atop by a wire nail are driven to establish the grid lines of the building. These pegs are driven at places such that they won’t be disturbed by field work etc. Usually they are driven with a distance of 1.5 meter from the grid line.
The diagonals of the main rectangle are checked to determine its accuracy. Accurately set up main rectangle is then subdivided to obtain the consisting gridlines. These are obtained by the using structural drawings, Theodolite and steel tape. Nylon threads are stretched between the pegs to obtain the gridlines when necessary.
Usually apart from the pegs depicting the main grid lines, pegs which show the 500mm off sets are also established during the setting out process to facilitate the construction that follows.