The Technique of Construction Estimating

The construction estimating is the calculated amount of various required items of work, and the expenses likely to be incurred there on. The total of the probable expenses to be incurred on the work is known as estimated cost of the work. This cost is a close approximation of its actual cost. The agreement of the estimated cost with the actual cost will depend on accurate use of estimating methods and correct visualization of the work, as it will be done. Doing accurate estimating is very important as the success of the project largely depends on estimating methods. Under estimating may result in the client getting an unpleasant shock when tenders are opened and drastically modifying or abandoning the work at that stage. Over- estimating may loose the engineer or estimator his client or his job, or in any case his confidence.

Estimating is the most important of the practical aspects of construction management, and the subject deserves the closest attention of one aspiring to a career in the profession. It is a comparatively simple subject to understand; however, as it brings one up against practical work, methods and procedure, knowledge of it cannot be acquired without close application.

Data Required for Preparing an Estimate:

In order to prepare a detailed estimate the estimator must have with him the following data:

1. Plans, sections and other relevant details of the work.

2. Specifications indicating the exact nature and class of materials to be used.

3. The rates at which the different items of work are carried out.

To enable an estimator to take out the quantities accurately, the drawings must themselves be clear, true to the fact and scale, complete, and fully dimensioned. The estimator has also to bear in mind certain principles of taking out quantities.

Steps in Preparation of an Estimate:

There are three clearly defined steps in the preparation of an estimate.

1. Taking out quantities

In the first step of taking out quantities, the measurements are taken off from the drawings and entered on measurement sheet or dimension paper. The measurements to be taken out would depend upon the unit of measurement. For example, in the case of stone masonry in superstructure, length, thickness and height of the walls above plinth level would be taken out from the drawings and entered on the measurement sheet, whereas, in the case of plastering only the lengths and heights of the walls would be entered. Obviously, the unit of measurement in the first case is cubic meter and that in the second case is square meter.

2. Squaring out

The second step consists of working out volumes, areas, etc. and casting up their total in recognized units.

3. Abstracting

In the third step all the items along with the net results obtained in the second step are transferred from measurement sheets to specially ruled sheets having rate column ready for pricing.

The second and third steps above are known as working up. All calculations in these stages and every entry transferred should be checked by another person to ensure that no mathematical or copying error occurs.