Two
Methods for Setting Out a Building on Site

Before a building can be constructed on site, it must be
first set out. In civil engineering, building plans are usually drawn on paper
before they can be transferred to ground as tangible physical bearing elements
known as structures, in this case, buildings.

Setting Out which
is also called Markings, is the
process of establishing centre lines for the transfer of foundation plans to
ground.

In this treatise, I will treat with you, two basic
approaches to set out a building on site for construction in civil engineering.

In setting out, the centre lines and foundation of the
building are marked out before excavation as per the layout plan. Setting out
could also be called Layout Marking, and
it involves driving the pegs into the ground, and construction of the pillars.

In the first approach to setting out, the center line of the
longest outer wall of the building is marked on the ground, by stretching a
string between the pegs embedded in the pillars. This centre line serves as
reference point for all other walls of the building.

To set out using this approach,

·       
Project the pegs above ground level, and drive
them at a distance of about 2m from the edge of excavation, in order to protect
them from disturbance during the excavation.

·       
Stretch a string joining the corresponding pegs
at the two edges of the line

·       
The boundary of the trench to be excavated can
be marked out with dry line-powder.

·       
The centerlines of other walls perpendicular to
the longer outer wall, are then set at right angles

·       
The right angles could be set by the 3-4-5
method, which entails setting triangles with 3, 4 and 5 units long sides.
Length increments are multiples of these values. The diagonals should also be
checked for ensuring right angles at all the corners.

·       
The top of the pillar is plastered, and is set
at the same level, preferably the building’s plinth level.

·       
Pegs are embedded in the pillars, and corresponding
lines are marked on the wet plastered surface, by pressing the stretched strings
by trowel on the surface.

·       
The outside lines of the foundation trench are
marked in the same way.

·       
Before excavation commences in earnest, the
strings are stretched between the outside lines of the excavation trench,
marked over the pillars, and the cutting lines are marked with line powder on
the ground.

The following should be noted while carrying out the setting
out;

·       
The diagonals should always be checked for right
angles.

·       
All necessary steps should be made to ensure
that the pillars around the pegs do not get disturbed during excavation.

The second approach to setting out of a building on site I
will highlight below, is similar to the first method given above.

Before carrying out the setting out, make sure you have the
required tools and instruments for setting out, such as hammers, lines, set
squares, spirit level, pegs, tape, etc.

·       
Also endeavor to locate the temporary benchmark on
site which could be a peg set to the DPC height, block, or any other such
material meant to serve as a datum.

·       
Locate the building corner mark drawn on the
curb on the site.

·       
Start by placing one edge of the building well
out of the building corner mark, at a considerable distance which may be
indicated in the building plan.

·       
Drive a peg into the ground at this distance.
Also drive a nail into the peg at the midpoint for the attachment of line.

·       
Make the length of the building line low enough
to clear the other corner of the building.

·       
Establish a building line parallel to the curb
at this defined distance using a line (string) extending from the nail driven
into the midpoint of the first peg to another peg on the same parallel line.

·       
Transfer the building corner mark from the curb
unto the building line.

·       
With a line attached to this peg, intersect it
with the building line. This intersection forms the first corner of the
building.

·       
From this intersection, measure the length of
the building along the building line, to locate the second corner of the
building.

·       
To establish a side of the building
perpendicular to the building line, use the 3-4-5 method, which could be
obtained using a 3, 4, 5 set square, or by a wise utilization of the tape such
that, an initial three meter is established, and the rest two sides being 9m,
is divided accordingly, to obtain a four and a five respectively, such that the
longer side of this arrangement forms the hypotenuse of the triangle.

·       
The four-meter position defines the line of the next
wall of the building. Measure along this line to establish the third corner of
the building.

·       
Repeat the 3, 4, 5 method to position the fourth
corner of the building.

·       
Check that the distance between the front
corners is the same with the distance between the rear corners.

·       
Check that both diagonals are the same in
length.

·       
Extend lines beyond each corner to position the
profile boards.

·       
Mark unto the profile board the position of the
first line of the outer brick.

·       
Measure the overall width of the cavity wall.

·       
Also mark on the profile board the width of the
foundation. Finally transfer the markings to the outside surface of the profile
boards.

·       
Transfer the height of the temporary bench mark
to a datum peg at each corner of the building and reverse the level.