Methods of Estimation for Building Works
When it comes to estimating the quantities of building materials such as earth work, foundation concrete, brickwork in plinth and superstructure, there are different methods that can be employed. Three of the commonly used methods are the long wall-short wall method, centerline method, and partly centerline and short wall method.
The long wall-short wall method involves estimating the quantities of materials needed based on the length of the long walls and short walls of a building. The length of the long walls is multiplied by their height and thickness to arrive at the required quantity of materials, while the same is done for the short walls. The estimated quantities for both types of walls are then added together to get the total quantity required.
The centerline method involves estimating the quantity of materials required based on the centerline of a building. The centerline is taken as the reference point for measuring the length and width of the building, and the required quantities of materials are estimated based on these measurements.
Finally, the partly centerline and short wall method is a combination of the first two methods. This method involves estimating the required quantities of materials based on both the centerline and the length of the short walls of a building. The estimated quantities for both approaches are added together to get the total quantity required.
Overall, each of these methods has its strengths and weaknesses, and the choice of which method to use depends on factors such as the size and complexity of the building, the materials being used, and the preferences of the estimator.
Long Wall – Short Wall Method
This method involves considering the wall running along the length of the room as the long wall, and the wall perpendicular to it as the short wall. To determine the length of the long wall or short wall, the first step is to calculate the centerline lengths of each individual wall. Once this is done, the length of the long wall (measured from outside to outside) can be determined by adding half the breadth of the wall to its centerline length at each end. On the other hand, the length of the short wall is determined by subtracting half the breadth of the wall from its centerline length at each end. Typically, the length of the long wall decreases from the earthwork to the brickwork in the superstructure, while the short wall increases. To determine the quantities of materials needed, these lengths are then multiplied by the breadth and depth of the wall.
Centre Line Method
The method being referred to here is suitable for walls that have similar cross sections. In this method, the total centre line length is multiplied by the breadth and depth of each item in order to calculate the total quantity at once. However, when cross walls or partitions or verandah walls join with the main wall, the centre line length gets reduced by half of the breadth for each junction. Therefore, these junctions or joints need to be studied carefully while calculating the total centre line length. It is important to note that the estimates prepared using this method are both accurate and quick.
Partly Centre Line and Partly Cross Wall Method
The centre line method is commonly used when the external walls of a building have a consistent thickness, while the internal walls have varying thicknesses. In this approach, the centre line method is applied to the external walls, while the long wall-short wall method is used for the internal walls. This method is particularly suitable for situations where different thicknesses of walls and foundations at different levels are involved. As a result, many engineering departments adopt this method in their practices due to its versatility in accommodating varying wall thicknesses and foundation levels.