Estimation for Building Works | Centre Line Method | Long and Short Wall Method

Estimation for Building Works

The quantities of various items such as earthwork in excavation, foundation concrete, brickwork in foundation and plinth, brickwork in the superstructure, etc. can be estimated by any of the following three methods

1. Centre Line Method
2. Long and Short Wall Method
3. Crossing Method 

1. Centre Line Method

In this method of estimation, the total center line length of walls in a building is first calculated, then the center line length is multiplied with the breadth and depth of respective item to get the total quantity at a time.

Fir different sections of walls in a building, the center-line length for each type shall be worked out separately.

In the case of verandah walls or partition joining with the main wall, the center-line length shall be reduced by half of the breadth of the layer of the main wall that joins with the partition or verandah wall at the same level. A number of such pints arc simnel first to calculate the center-line length.

By this method, estimates may be prepared more quickly, and this method is as accurate as of the other methods.

Only in the case of an unsymmetrical wall, which is generally rare, no advantage may be claimed by this method over others as the center-line length varies at every layer.

But to estimate circular, hexagonal, octagonal, etc. shaped buildings, this method shall specially be adopted.

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2. Long and Short Wall Method

In this method the longer walls in a building (generally in one direction) are considered as long walls and measured from out to out: and the shorter or partition walls, in a perpendicular direction of the long walls, are considered as short walls and arc measured from in-to-in for a particular layer of work.

These lengths of long and short walls arc multiplied separately by the breadth and height of the corresponding layer and are added to get the quantity.

Such lengths of long and short walls vary in every layer of footing. To calculate the lengths of long and short walls determine first their centre to centre lengths individually from the plan.

Then the length of the longwall, out-to-out may be calculated after adding half breadth of a wall at each end with its centre to centre length.

Thus the length of the short wall measured in-to-in may find out after subtraction half breadth at each end from its centre to centre length.

Length of long-wall generally decreases from earthwork to brickwork in the superstructure and in the case of a short wall, its length increases.

In some of the working examples, it may be noticed that a wall is considered as a short wall at one end and as a long wall at the other end.

Such a case arises in a wall that joins as a long wall with another long wall previously considered.

The joining end of the wall later considered as long wall is actually treated as a short end, and such a wall is named as Long-Short wall.

Also, read: What Is Construction Contract | Types of Engineering Contracts | Percentage-Rate Contract

3. Crossing Method 

In this method calculate the overall perimeter of the building and subtract from this four times the thickness of the wall to obtain the centre-line length.

This method is now rarely used.

Examples,

Example, By Centre-Line Method 

To estimate the quantities, calculate first the total length of the center-line which remains constant for varying widths of works, and multiply this constant length of the centre-line with the respective breadth and height.

Thus quantities of all items may be calculated easily.

The total length of center-line =  2 [ (3m + (2 x ( 30 cm/2) ) + (2.5m + (2 x ( 30 cm/2) )]

The total length of center-line =  12.2 m

Elements of Building Estimate use Centre-Line Method 

Example, By Long and Short wall Method 

Center to Center length of long walls = 3 + (2 x 0.115) = 3.3  m

Center to Center length of long walls = 2.5 + (2 x 0.115) = 2.80 m

The length of long walls out-to-out and short walls in-to-in vary in every laver of footing.

To calculate the length of long walls add a half breadth of that layer at each end with the centre to centre length and for short walls subtract half breadth of the layer from each end.

Lengths thus obtained may also be verified from the plan as shown in the above fig.

Elements of Building Estimate use Long and Short wall Method