Different types of Estimation Methods used by Civil Engineers or Estimators

Different types of Estimation Methods are used by Civil Engineers or Estimators. 

Some common Quantity and Cost Estimation methods used in civil engineering construction are explained in brief below:

Estimators must read the drawings, specifications, and types of works to be constructed before the estimation of cost and quantity. Different types of cost such as direct and indirect, overheads, etc are calculated to provide a detailed quantity and cost estimation of a project to be constructed.

Types of estimation:

1. Approximate estimate :

It is also called budget, preliminary estimate. This type of estimate is ready within the initial stage of a project. To give a clear plan to the owner (client) regarding the amount of cost required for the project and to get the approval from necessary sanctionative bodies (eg: from banks to get a loan). Documents like project drawing plans, details about the land including electricity & water supply and a full clear report are necessary to carry out the estimate. Commonly the approximate estimate is calculated with relevant to the previous experience.eg: To calculate the estimate for a house, a previously (& also recently) completed a similar house will be considered. Here the estimator already knows the rate for 1m2 area & with that he/she calculates the cost estimate for the newly proposed area (of the similar house).

Approximate estimate = Rate of 1m2 (already known value) X proposed area (m2)

2. Plinth area estimate:

Plinth area estimate will be achieved by multiplying the values of plinth length, plinth width & plinth area rate. Here the plinth area is referred to as, external plinth area of the building at floor level. Simply it will be additionally declared as the roof covered space of a building. Plinth area rate is derived by dividing the total cost of a previously constructed building by the plinth area of the previously constructed building.

Plinth area estimate = plinth area X plinth area rate.

Plinth area = plinth length X plinth width

Plinth area rate = Total cost of an antecedently built building / Total plinth area of that building.

There are some restrictions in calculating the plinth area of a building and a few areas need to include or exclude when calculating. Among that, areas which can include are,
Floor area with area of walls at floor level excluding the offsets of the building, internal shafts of sanitary fittings within 2 sq.m., lifts, air conditioning ducts, area of porch at floor level (cantilever half can’t be included), area of barsati – a room on the terrace or roof top with veranda outside. Areas which can’t include are, Area of lofts, open balconies /nonenclosed balconies, fascia, towers which project above terrace level, louvers & vertical sun breakers. Documents such as line plan with complete specifications & costs for services such as water, electricity should be attached with the estimate.

3. Cubic content estimate :

This type of estimate done by multiplying the volume of the building by the unit cubic  rate achieved from the antecedently (also recent) estimate. This type of estimate is a bit more correct than preceding methods and principally appropriate for multi-storied buildings. Here the cost of corbelling (corbel – a piece of stone, wood, brick, or different building material, projected from the face of a wall and usually accustomed support a cornice or arch), cornice and other works like that are neglected.

Cubic content estimate = Volume of the building X unit boxlike rate (known value)

The volume of the building = plinth area (length X breadth of the proposed building) X height of the building (floor to roof top)

Unit cubic rate = total cost of the previously built building / total volume of that building.

4. Annual repair estimate and special repair estimate :

These estimates are prepared so as to maintain the constructed component in good shape. Works that attached when considering repair works, white washing, painting, plastering works, patching works & etc. The special repair estimate is prepared in situations where the costs of materials increased when compared to the annual repair estimate cost.

5. Revised estimate:

This estimate is prepared once the rate of previously submitted estimate will increase by five-hitter or over that. But here the reason for the preparation of estimate must have a strong & valid reason like a sudden increase in the cost of materials. The reason and comparative statement between two estimates ought to be annexed with the revised estimate.

6. Supplementary estimate :

This type of estimate is prepared once there's a necessary situation of supplementary work, to progress out the original work. The annexure of originally prepared estimate & supplementary calculable quantity of the originally prepared estimate once submitting for requesting approve.

7. Detailed estimate:

Detail estimate is prepared with the help of a complete set of contract documents. The preparation of detailed estimate will do beneath two phases such as work out with quantities of various works and calculate the cost of every work.

work out with quantities of different works: The whole construction work procedure is divided into categories such as excavation and earthwork, concrete work, formwork, reinforcement, masonry work, roof covering and roof plumbing, carpentry, painting and decorating, plumbing, electrical installation and etc.

The measurement procedure is done with the help of drawings/plans and then they are entered in measurement. Measurement sheet is a prescribed form which contains a number of columns to enter the respective measurements and descriptions about the works. Finally, the measuring columns are increased to get the required quantity.

Measurement Sheet of  Detailed Estimate

·         Calculation of the cost of each work: The already obtained quantities are used to obtain the cost of each work. Calculated costs of each work item are summarized in order and that document is called as an abstract sheet.

Abstract Sheet of Detailed Estimate

A detailed estimate should have documents such as the report, specifications, drawings/plans, design charts and schedule of rates. Factors such as, material quantity, transportation of materials, location of site, labour charges, cost of equipment (commonly allowed: 2% of the estimated cost), overhead charges (commonly allowed: 2% of the estimated cost), contingencies & unforeseen (commonly allowed: 4% of the estimated cost) items are needed to consider well while preparing the detailed estimate.

In this way, the different type of cost and quantity estimation of civil works is carried out. Estimator should apply the prevailing rates of the respective time and location where the project is to be carried out. The rates provided in the books may not apply for all the period and locations. Rates analysis and district rates of the respective district or municipalities must be applied of the respective time for cost estimation of the project.