The setting out of a building simply means the marking out of walls, columns, foundation widths and other important elements of a building about to be constructed. Since accuracy is the key, setting out must be undertaking by competent persons.
Examples of persons that can set out a building are civil engineers and land surveyours.
All setting out work should be thoroughly checked by a different personel using different methods.
It is usually the responsibility of the contractor to set out buildings using information provided in the architectural and structural drawings.
How buildings are set out
The first task in setting out of a building is to establish a base line upon which all setting out will be related. The base line often coincides with the building line.
The building line is a line in front of which no construction is permitted by the building/ town planning authorities. For example, the building line for a small estate road can be at a specified distance of say, 3m, from the road way;
After the building line is established, a perimeter of profile boards is then set out to surround the actual building area at an offset of about 2m or more. This is to allow adequate room for marking out and excavation of trenches.
The top of the profile boards should be at the same level .
The corners must be at 90 angles with the use of builders square or theodolite. Diagonal checks must be carried out to confirm accuracy of the setting out work.
The next step is to mark out on the profile boards; wall, column and trench positions. Ropes tied on the marked positions of profile boards and transferred to the corresponding opposite directions ( of marked positions on the opposite profile boards) will show the width of trenches to be dug out.
The width positions can be marked on ground by use of dry lime or similar powder.
Another method is to mark out the exact building outline using corner posts firmly driven into the ground (see 2nd figure).
With nail driven into the center of the corner posts, cord is tied from one corner to another, connecting all corners. The outline can then be transferred/ marked on ground using dry lime or similar powder. Using the building outline, profile boards can then be erected for excavation of trenches and construction of walls and columns
For larger structures such as large framed buildings, setting out is best carried out by a theodolite or total station equipment. These types of buildings are usually related to a grid system, the intersection of the grid being the center point of an isolated pad footing. The total station can be used to accurately establish the grid system on ground, marking the intersections of grids with stout pegs.
Once grid has been set out, offset pegs or profiles can be fixed clear of subsequent excavation work.