Building Estimation By Center Line Method
In this method, sum total length of center lines of walls, long and short has to be found out. Find the total length of center lines of walls of the same type. Long and short have the same type of foundation and footing and they find the quantities by multi-plying the total center length by the respective breadth and height.
In this method, the length will remain the same for excavation in the foundation for concrete in the foundation. For all footings and for the superstructure. (With slight difference when there are cross walls or the number of junctions). This method is quick but requires special attention and consideration at the junction, meeting points of cross walls, etc.
Read More: Residential Building Estimation Excel Sheet
How to Calculate Center Line In Plan
Center line length of one wall = inner dimension of room + Wall thickness
= Inner dimension of room + ½ x Wall thickness of one side + ½ x wall thickness of other.
- Centre line length of horizontal wall
= 4 + 0.45 + 0.45
= 4.90 m
- Centre line length of vertical wall
= 3 + 0.45 + 0.45
= 3.90 m
Total Length of excavation for foundation
= 2(4.90 + 3.90)
= 17.6 m
Quantity of excavation for foundation
= Total length of centre line of walls x breath of trench x Depth of trench
= 17.6 x 0.9 x 1.2
= 19.01 m3
For rectangular, circular or polygonal buildings having no inter or cross walls, this method is quite simple but for buildings having a cross or partition walls, for every junction of partition or cross walls with main walls, a half breath of the respective item or footing is to be deducted from the total center length.
Net Centre line length – (½ x breath of wall x number of the junction)
Following Points in relation to the center line method should be noted.
- The term junction is used to indicate the meeting points of cross walls or partition walls with main walls.
- For instance, if there is one cross wall there will be two junctions. At the corner of a building, no junction is formed.
- For rectangular building with no cross wall there will not be any junction and hence no deduction from the centre line length will be required. It is fact that is certain portion taken twice is counter balanced by same amount portion left out at the corner.
- The breath indicates the width of item whose centre line is being worked, for instance it will be the width of trench of excavation and foundation concrete. But for brick masonry up to plinth or for superstructure will be equal to the corresponding thickness of wall.
For a two-room building with the inner cross wall, two junctions will be formed shown in fig.
Total Centre Line length
= (2 x AB + 2 X BC + EF)
= (2 X 9.50 + 2 X 5.5 + 5.5)
If this center line length is multiplied by the width and depth, the quantity at junction P and Q will come twice, the quantity of each being equal to ( ½ x width x Depth ).
Hence the quantity of these two junctions must be deducted to get the net center line length.
Net Center Line Length
= (Total Centre line length – (width/ 2) x No. of junction)
= 35. 50 – (½ x 0.90) x 2
= 34. 60 m
Center Line Method of Building Estimation Example
Let’s take on the example of a building plan and calculate its quantity by using the center line method of estimation.
Building Estimation by Center Line Method Excel Sheet
Download Building Estimation Excel Sheet
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