Before contractors can begin a construction project, they first need to lay the building plans on the ground. This is the process of making the outline of the structure, to the exact dimensions, on the location of where it will be built. The building plan will show contractors where to dig and lay the foundations for the building.
The building plan is often marked by pegs and string, but some contractors like to use white paint on the ground. Pegs are hammered into the ground and attached by a string along the centreline of walls. Contractors need to make sure that the pegs and string follow the architect’s drawings perfectly.
Steps to laying a building plan on the ground
- Clear any long grass and rocks from the construction site where the building will stand. Remove any debris and skim off the topsoil. This will make the marking process easier and clearer.
- From the architect’s drawing, start by hammering a peg into the ground at one of the corners of the building (call it point A). Measure the distance of the wall, using the architectural plan as a reference, and place another peg in the ground where the next corner of the wall will be (point B).
- Place a peg two metres away from point A and point B and connect these two pegs with the string. These pegs (call them A1 and B1) will help contractors excavate the foundations later without having to move the string or corner pegs.
- Repeat this process of placing pegs at all the corners of the walls (points C and D) and placing additional pegs two metres away. Attach all the outer pegs with string. Each corner point should have two pegs (corner A will have peg A1 joining B1 and A2 joining D2). Where the strings cross will mark the exact corner of the walls.
- To make sure that the corners are 90°, the centre points of the rooms needs to be calculated. Measure the distance between opposite corners (point A and point C) on the architect’s drawings. Make sure that the real distance between the pegs at point A and point C match the distance on the drawing. You may have to move the pegs a bit to make these diagonal measurements are exact.
- Where the diagonal strings cross is the centre point of the room. The opposing walls (AB and CD or AD and BC) should be the same distance from this centre point.
- Once all the strings are laid, the contractors can start excavating the foundations. The extra two metres of string at each corner will allow the contractors to dig the foundations without having to excavate any corner pegs. The strings will be used as a guide for the centreline of the walls.
- Some contractors like to spray white spray paint on the ground or use lime to demarcate the path of the wall underneath the strings. This just helps to dig the foundation more accurately.
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