Basic Setting Out of a Building

Well if you are a Civil engineer having a building plan in hand and not knowing what to do where to start this post will help you a bit.Yep i mean only a bit not much because i'm only discussing the very basics in this post.

Okie... first to begin with what is a setting out of a building?. We can simply answer to that question like this.Architects and other people who are dealing with the design of the structure gives us a plan.Its only a paper showing some lines , dimensions and levels etc.To add some value to that we can say them structural and architectural drawings.As a man responsible for the construction we need to give life to those plans in physical terms.In order to do that we need to locate the geometrical items of the building in correct places according to the drawings. This is the process known as the setting out of the building.

got it? .or confused??? ... alright here it is in old text book way..

Basic setting out of a building is the process of locating the positions of the structural parts of a building in geometrical construction.

Enough of introductions, back to the topic again.
So you have a plan in hand and a land to build.Where to start and how to start?

We need  a base line first.It is any geometrical boundary that we can find in the site.In some architectural drawings it is specially mentioned.If not contact your consultant and come to an agreement on what to chose as the base line.In simple two story or three story building construction we can simply choose a perimeter wall    or any permanent structure nearby.From that baseline we can start our work.We can start measuring distances from that .

Now choose a position as your 0.000 level.Most of the time it is mentioned in the drawings.If not discuss with your consultant and come to an agreement to avoid future disputes.Pay attention to flood level and natural water tables etc.. when selecting the level 0.000.

Now have a look at your drawings(plans).Select the biggest rectangle or the square that is on the drawing.

But why on earth do we need the biggest one? cant we start with the smallest one? NO. YOU NEED THE BIGGEST ONE .!!

Biggest Rectangle in Yellow 

The reason is that we do the setting out process in a method called "WHOLE TO PART". We start with the biggest and subdivide it to obtain the smaller ones.This method help us to eliminate the errors and introduce a way to crosscheck.

Remember the setting out work must always provide independent checks for better accuracy.

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.