12 Types Of Estimate | Types Of Estimation | Methods Of Estimation In Civil Engineering

Introduction:

An estimate is a technique to calculate the quantities of various items of work, and the expenditure likely to be incurred thereon.

The total of these approximate expenses to be incurred on the work is known as the estimated cost of the work. The approximate cost of a work is a close approximation of its actual cost.

There are 12 Types of Estimates in civil engineering Approximate or Rough Estimate, Plinth Area Estimate, Service Unit Method, Floor Area Method, Carpet Area Method, Typical Bay Method, and Cost Comparison Method.

What is Estimation?

Estimation is the technique of estimating the various quantities of work and the expected expenses to be incurred on a particular work or project to execute.

In case the funds available are less than the estimated cost the work is executed in part or by reducing it or specifications are altered.

Estimation gives an approximate idea of the time required for the completion of the work. The estimate is required to invite the tender and quotations and to arrange a contract.

The estimate is also essential to control the expenditure during the execution of work. An estimate decides whether the proposed plan matches the funds and budget available or not.

The rate used in the estimate should check with the current standard schedule of rates (SOR) & in the case of quantity, it should check with the standard data book.

Types of Estimates

The followings are Types of Estimates in Construction

1. Preliminary or Approximate or Rough Types of Estimates

This type of estimate is also called the budget, a preliminary estimate. This preliminary estimate is prepared in the initial stage of the project to give a clear idea to the client about the funds needed for the project and to get approval from necessary sanctioning bodies (for example: to get loans from banks).

Documents like project drawing plans, details about the land including electricity & water supply system and sanitary system a full clear report are necessary for the previous experience.

Eg: To calculate the estimate for a house, a previously completed similar house will be considered.

Here the estimator already knows the rate for 1m2 areas & with that he/she calculates the cost estimate for the newly proposed area of a similar house.

Approximate estimate = Rate of 1m2 area(already known value) x Proposed area (m2)

The preliminary estimate may be prepared in various ways for different work and structures as:

A) For Building:

Service unit method
Plinth area method
Floor area method
Carpet area method
Cubical content method
Typical bay method
Approximate quantity method

B) For Road and Highways:

For roads and highways, it is calculated per kilometer basis depending on the nature of the road, width, thickness of metaling, etc.

For 10 km of a state highway, the approximate cost is Rs.6,00,000/- per km.

Total Cost = 10 x 6,00,000

= 60,00,000 Rs. = Rs. 60 lakh

C) For Irrigation Canals:

The cost of the Irrigation canal is calculated per kilometer basis depending on the capacity of the channel.

The approximate cost of a 10 km length of irrigation channel of 3 cubic meters per sec capacity @ Rs. 1,00,00 per km.

Total cost = 10 x 1,00,00 =10,00,00 Rs = Rs. 10 lakh.

C) For Bridge:

The cost of the bridge is calculated per running meter of span depending on the roadway, nature, depth of foundation, types of structure, etc.

The approximate cost of a bridge o 4 spans of 50 m each span @ Rs. 50,000 per running meter of the span is

Total cost = (4×50) x 50,000

= 1,00,00,000 = Rs. 1 crore

E) Water Supply and Sewerage Project:

It cost is calculated per head of population served.

Approximate cost of water supply for a population of 80,000 @ Rs. 100 per head comes to 80,000 x 100 = 96 lakhs.

F) Over Head Water Tank:

Its cost is calculated on basis of the capacity per liter of the tank depending on the type of structure, the height of the tank, etc.

Approximate cost of an overhead RCC tank of 1 lakh liter capacity @ Rs. 3 per liter works out to be 1,00,000 liter x 3 = Rs. 3 lakhs.

2. Plinth Area Estimates

In this type of estimate, the plinth is found by multiplying the values of the length of the plinth, the width of the plinth, and the plinth area rate.

Here the plinth area is referred to as the external plinth area of the building at floor level. Simply it can be also stated as the roof-covered area of the building.

The plinth area rate is derived by dividing the total cost of a previously constructed building by the plinth area method.

Documents such as a line plan with complete specifications & costs for services such as water, and electricity should be attached with the plinth area estimate.

Plinth area estimate = Plinth area x Plinth area rate

Plinth area = Plinth length x Plinth width

Plinth area rate = Total cost of a previously built building / Total plinth area of the building.

In this method cost of a 1 m3 area is calculated from the cost of similar plinth area construction in the nearby area which is known as the plinth area rate.

Estimate cost = Plinth area x plinth area rate for 1 m2 area

For Example,

A building has a plinth area of 200 m2 and the plinth area rate in this area s Rs. 3500/- per m2.

Estimated cost = 200 x 3500 = 7,00,000 Rs

There are some restrictions in calculating the plinth area of a building project and some areas have to include or exclude when calculating the cost.

Among that, areas include are, a floor area with an area of walls at floor level excluding the offsets of the building, internal shafts of sanitary fittings within 2m2, lifts, air conditioning ducts, an area of the porch at floor level, a room on the terrace or rooftop with verandah outside.

Areas that can’t include are an area of lofts, open balconies/un-enclosed balconies, and fascia, towers that project above terrace level, louvers & vertical sun breakers.

3. Service Unit Method

In the Service Unit Method, the Service Unit indicates the most important unit in a structure. The entire structure is divided into a number of service units.

For example, in a school building, the service unit is in the classroom. Then, the approximate cost of structure = Number of service units in the structure x cost of service units in a similar existing structure.

The approximate estimate of the school building is prepared on the basis of the service unit and the service unit for the school building is the classroom.

The service units for various structures are given in the below table.

Sr. No.	Types of Construction	Service unit
1.	School, Collage	Classroom
2.	Hospitals	Bed
3.	Hostel	Students
4.	Hotel	Room
5.	Theatre(Cinema)	Seat
6.	Stadium	Seat
7.	Jail	Kotani
8.	Stable	Animal
9.	Water Tank	Litre
10.	Dam	Hectare Meter
11.	Water Supply Scheme	Person
12.	Road	Kilometer
13.	Canal	Kilometer
14.	Bridge	Meter
15.	Power Station	Kilowatt

Types of Construction and Their Service Unit (Service Unit Method)

While Deciding on a service unit of similar construction the following points should be noted.

1) Change in cost of land

2) Change in the price level of different materials.

3) Change in rate of labor.

4) Change in the specification of construction.

This type of estimate is generally used in places where units are easily defined.

4. Floor Area Method

The floor area is calculated by deducting the area of the wall from the plinth area.

Floor area = Plinth area – Area of wall

In the calculation of the area of walls, the thickness of the wall shall be inclusive of finishes and dado if the height of such finish is more than 1 m from the floor finish.

The following points must be included in the wall area:

i) Door area another opening in the wall.

ii) Built-in cupboard, almirah, etc. appearing within a height of 2.2 m from the floor.

iii) Flues that are within the wall.

Example,

Estimate cost = Floor area x Floor area rate

Let, one building gas floor area of 100 m2, and the floor area rate is 4000 Rs.

Estimated Cost = 100 x 4000 = 4,00,000 Rs.

5. Carpet Area Method

The carpet area is the floor area less the area of the followings portions (as per IS 3861)

Verandah
Corridor, Passage
Entrance hall and Porch
Staircase
Bathroom and W.C.
Kitchen and Pantry
Store, Machine Room for lift
Shaft for sanitary pipes etc.

Estimated Cost = Plinth area x plinth area rate

6. Typical Bay Method

This method is useful in the case of a building that has several similar bays. A bay is a space from the center to the center of two successive columns. A typical interior bay is selected and its total cost is worked out. Then,

Approximate cost of proposed building = numbers of bays x cost of one bay

The following points are to be noted:

Necessary corrections should be made for end bays due to end walls.
Sufficient allowance should be made to compensate for the small things that are overlooked.

7. Cost Comparison Method

This method is suitable for the estimate of the prototype structure. For example when prototype staff quarters or railway stations etc, are required.

to be estimated approximately then the estimate for such prototype work is prepared by comparing the previous cost with the present market rates, normally by increasing the past cost on a percentage basis.

Such an estimate can be prepared in a short time even during meetings also.But expert knowledge is necessary to estimate the present cost of construction as compared to previously recorded costs.

8. Cubic Content Method

In this method estimate is done by multiplying the volume of the unit cubic rate achieved from the previously (also recent) estimate.

The cubic Content Method is a little bit more accurate than the above-mentioned methods and mostly suitable for multi-storied buildings.

The price of corbelling (corbel-a piece of broken stone, wood, brick, or any building material, projecting from the face of a wall and generally used to support a cornice or arch, etc), cornice, and other works like that are neglected.

Cubic content estimate = Volume of the building or structure x Unit cubic rate (original value)

The volume of the building = Plinth area (length x breadth of the proposed building) x Height of the

building (floor to rooftop)

Unit cubic rate = Total cost of the previously constructed building / Total volume of that building

9. Annual Repair Estimate or Special Repair Estimate

It is used for annual repair estimates or special repair estimates. These estimates are prepared for the purpose to maintain the constructed element in good condition.

Works that included when considering repair works, whitewashing, painting, plastering works, patching works, sanitary works, etc.

A special repair estimate is prepared in a situation where the costs of materials increased when compared to the annual repair estimate cost.

10. Revised Estimates

A revised estimate is prepared when the cost of the previously submitted estimate increases by 5-7% or more than that.

But here the reason for calculating the estimate must have a strong & valid reason like a sudden increase in the cost and expenses of materials.

The reason and comparative statement between the two estimates should be annexed with a revised estimate.

11. Supplementary Estimate

This type of estimate is prepared when there is a necessary situation for supplementary works, to progress out the original work.

The annexure of the originally prepared estimate and supplementary amount of the originally prepared estimate when submitting for requesting approval.

12. Detailed Estimate

It is the most important type of estimate for building construction. A detailed estimate is prepared with the help of a complete set of contract documents.

The preparations of the detailed estimate can do under 2 phases such as working out quantities of different works and calculating the cost of each work.

a) Work out with quantities of different work:

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, etc.
Decoration of the approximate estimate depends upon the area to be decorated.
The measurement-taking procedure is done with the help of drawings/plans and then they are entered into the measurement.
A measurement is a form that contains a number of columns to enter the respective measurements and descriptions of the works. Finally, the measurement columns are multiplied to get the necessary quantity.

b) Calculation of the cost of each work:

The already obtained quantities are used to get the cost of each work. Estimated costs of each work item are summarized in ascending order and that document is called the Abstract sheet.
Detailed types of estimates should include all the related documents such as reports, specifications, drawings & plans, design charts, and schedule of rates(SOR).
There are various factors that affect the cost of each work such as material quantity, transportation of materials, location of the site, labor charges, cost of equipment (commonly allowed 2% of the estimated cost), overhead charges (commonly allowed 2.5% of the estimated cost), contingencies and unforeseen (commonly allowed 4-5% of the estimated cost) items are needed to consider well while preparing the detailed estimate. (Types of Estimates in construction)

FAQs:

What is an estimate?

An estimate is a calculation of the approximate cost or quantity of something, such as a project, product, or service. It is an educated guess based on available information.

What is a preliminary or approximate estimate?

A preliminary or approximate estimate is an early estimate of the cost of a project, based on limited information and assumptions. It is often used to help determine the feasibility of a project and to obtain initial funding.

What is a unit rate estimate?

A unit rate estimate is an estimate based on the cost of a specific unit, such as a cubic yard of concrete or an hour of labor. It is often used in projects where the quantities of materials and labor are known.

What is a negotiated estimate?

A negotiated estimate is an estimate that is negotiated between the contractor and the client, based on a detailed scope of work and other factors. It is often used in projects where the client has specific requirements or preferences.