Building Plan Setting Out
What is setting out?
This is the process of transferring the information provided in working drawing (plan) by the designing engineer or architect to the ground. This task is carried out by either a civil engineer who can be referred to as site engineer. Or a builder (someone that study building).
Building plan setting out is very important and sensitive in the development of any building or structure due to the following objectives;
- It established the excavation size.
- Also, it established the width and position of the wall.
- It reduces concrete wastage during trench blinding (foundation blinding).
The most important step in the setting out process is obtaining angle 90 degrees at the corners of a square or rectangular shape building. This can be done using the following methods/instrument.
- Site square (2) Total station (3) Builders square (4) Theodolite (5) 3-4-5 Traditional method.
Of all the methods mentioned above, the most commonly used methods and instrument are;
- The builders square method/instrument and (2) the traditional 3-4-5 method/instrument.
This is due to their easy access, operation, handling, and availability. The builders square and the 3-4-5 traditional method are the same in procedures except that; in the builders square, the instrument called builders square is used to check the angle 90 degree which is the major aim of the setting out while in the 3-4-5 method, calculated figures and measurement are used to check the angle 90 degree.
Setting Out Of a Building Plan
For a building plan setting out to be carried out perfectly, two major things must be considered. These are:
- baseline (2) The building line
The baseline: This is a straight line of reference with respect to which the building corners are located on the ground. E.g.
- Outer boundary of a road or curb (2) Boundary of the plot on which development is to be carried out.
The building line: This is the line in front of the building from which development (building) start. From the baseline to this line, no development is permitted. This can be referred to as compound space.
Materials Needed For Setting out Using 3-4-5 Method or Builders Square
The following are the materials needed for setting out using the two methods /instrument mentioned above.
- Pegs (2 x 2 purlins of about 2 ft sharpen at one end )
- The working drawing ( the building plan)
- Profiles (2 x 2 purlin of length 12 ft or 16 ft)
- Steel tape and surveyor or fiberglass tape
- Builders square
Setting Out Of a Building Plan Using Builders Square
The following are the stages to be taken when using builders square for your setting out.
- Choose your baseline depending on the situation of the site (close to road or isolated) to which all the setting out will be related and measure the distance to the building line as indicated in the working drawing and establish the first corner of the building with a peg let’s call it peg A
- Measure the distance to which the second corner will be placed and measure the distance from the baseline to this point as done above to establish the second corner with peg B, and make AB a straight and horizontal by tying a line and re-measure the distance AB to confirm with the working drawing.
- Take an offset of 600 mm to 1 m outward from peg A and B and toward the baseline horizontally depending on the plot space to establish more four pegs, C and D at peg A, E, and F at peg B.
- Fixed nail on each of the pegs and connect a line from peg E through B to peg C, D through A so that the lines will intersect at peg A and measure the distance as stated in the working drawing from peg A and mark it with peg G to establish the third corner and connect the line to peg G.
- Take off peg A and place your builders square intersect of line CB and DG with a foreman at peg G to control it while you check for angle 90 degrees with the builders square at intersect of line CB and DG. Once angle 90 degrees is achieved ask the foreman the pin down the peg G.
- Connect a line from peg E to peg F and let it pass through peg B to peg H to establish the fourth corner such that line FH and CE will intersect at peg B and take off peg B and place your builders square at the intersect with a foreman controlling the line at peg H. Once 90 degree is achieved, asks the foreman to pin down the peg and measure the distance BH to confirm with the stated figure in the working drawing.
- Repeat step three above to establish peg I and J at peg G, K and L at peg H respectively and connect a line from peg G to peg I, from peg I to J and to peg K and L passing through peg G and H respectively and extend the line on peg H to peg L.
Confirmation of The Setting Out
- Confirm the square of all the corners with the builders square. Also, measure the diagonals BG and AH which must be equal in length if all corners are well squared.
- Once the four corners are confirmed, the building plan has been successfully squared.
- Thereafter, connect line DF, CJ, IL, and EK with lines and pin down pegs at an interval of 1.2m along each of the lines mentioned above at equal height.
- Establish your profile board of purlin on the pegs horizontally with the aid of the lines and take off the lines.
- Mark out the excavation width and all other dimensions on the profile board with the aid of nails and use lines to connect respective points for proper excavation excise. See fig 1, 2 and 3 for details.
fig 1 fig 2
Note: the broken lines in fig 1 shows the line where the other pegs will be established. Also, the marking out of wall width, other demarcations, and excavation width. While the continuous lines show the establishment of the four corners of the building.